Done right, the HVAC in your home can make it very comfortable, and very healthy. One might even call it bad ass. But it needs to have a few relatively simple tweaks to be able to deliver what we call The 6 Functions of HVAC, and do it well:
The trouble is 87% of heating and cooling systems are replaced on an emergency basis. This means mindfulness of the 6 functions is overridden by “I need heat ASAP, and as cheap as possible” myopic urgency.
If you have an HVAC system (furnace, air conditioner, heat pump, boiler, etc.) that is over 10 years old, it’s a good idea to build a replacement specification now, before you find a gun to your head and a hand rummaging through your wallet. Otherwise, when it dies you’re going to get the first piece of equipment that the first guy who shows up wants to install, and it will almost certainly fail to make your home comfier or healthier.
Since these systems last 15-20 years, getting the equipment right avoids either replacing it twice (we have replaced very new equipment), or signing on to a long term bad relationship.
When people hire us we find the only consistent way to deliver better comfort through the 6 functions is to replace the system. Again, this is often replacing systems well before reasonable life expectancy. Think about how it feels to waste $8,000 - $20,000 replacing a system you recently replaced. It’s so wasteful!
We hate the waste, so we invented what we affectionately call BAD ASS HVAC. BAD ASS HVAC is a (pretty) simple system that can tackle the 6 Functions, and most HVAC contractors can install it.
Why are those 6 important? And what is BAD ASS HVAC? We’ll be exploring those over the next few months. Today we’ll talk about the first two - load matching and filtration.
We list the 6 functions in order of priority, and we’ve found load matching is the most critical for comfort.
Do you notice that your house is particularly cold on 40-55 degree days? Your HVAC is may be too large. If you graphed your temperature it would look like this, with air temperature going up and down quickly:
Furnaces and air conditioners are supposed to be sized to heat or cool on the coldest and hottest days of the year in your climate. At these temperatures the equipment should run continuously or near continuously. Calculating this “worst case load” takes some measuring and some math. The problem is without using a blower door to measure your home’s leakage, and looking at your energy bills, sizing your HVAC is a wild ass guess, with a broad variance of answers. For a LOT of reasons (fear, greed, urgency, ambivalence) people tend to lean way to the high side of the range.
Almost every furnace we’ve seen is at least twice as big as it needs to be.
So why does that matter?
About 60% of human comfort is based on radiant energy. Think about how pleasing a bonfire or sunny day is. Those are both radiant energy, and our bodies love it.
In our homes, radiant energy is given off (or sucked in) by the walls, floors, and ceilings around us. Right sized HVAC washes the walls, ceilings, and floors of your house with a slow steady stream of heat or cool. Nice even surface temperatures give off pleasing radiant energy just like a fire or the sun.
If you want to be comfy, we need to keep those surfaces within 2 degrees of the thermostat set point. To do that, we want our HVAC to be running almost constantly putting out exactly as much heating or cooling as our home needs at that moment - this is called “load matching”.
The trouble is, most home heating and cooling systems are single stage, meaning on or off. Compare that to your car:
With an oversized furnace or air conditioner all they can give you is a blast of heating or cooling. One speed means you don’t get “subtle.” It’s the Ice Bucket Challenge instead of a nice cool shower on a hot day.
To do “subtle” we need right sized, multiple stage HVAC. I dig deep into this in Chapter 3 of The Home Comfort Book.
How do you get right sized HVAC?
Imagine going into a clothing store and being told that a small, medium, large, XL, or XXL could fit you. But the clothing is $8000 per item, you can’t return it, and you can’t try it on.
That’s about what typical load calculations end up being. A load calculation takes characteristics of your house to help decide which size HVAC is right for your house on the hottest or coldest day of the year. The industry standard calculation is called a Manual J.
If you measure how much a house leaks using a blower door test, run an energy model and reconcile with how much energy the house is actually using per year, and your load calculations get much more accurate. You’ll know within ½ ton what size the house needs. Yes, perfect is hard to achieve, but we see most equipment oversized by 1.5 - 4 tons
Once you install right sized, multiple stage HVAC, you’ll notice how the rooms are more even, and the temperatures no longer race up and down. (The exception to this might be a very leaky room like a bonus room over a garage, and that would be uncovered during a blower door test that includes zonal measurements.)
Oversizing HVAC equipment is about the single biggest problem we see. Once installed, it’s nearly impossible to reduce its output, so if you choose wrong, the only way to fix it is to buy another HVAC system.
HVAC is only part of the comfort picture. If your house is leaky, you will have to address the leaks if you want comfort. HVAC will only fix so much. So if your house is leaky and you find yourself in need of HVAC, we advise installing equipment for the house you plan to have, not the one you have now. The house isn’t going to be fantastically comfortable anyway, and chances are it’ll be more comfortable 90% of them time if you undersize than if you oversize.
You want to size to where you are going, not where you are. Otherwise expect the air temperature in your home to race up and down, and the surfaces of your home to remain cold while literally sucking the heat out of you. Instead, make sure your HVAC is BAD ASS… more on that in a few months.
Did you know we breathe 3000 gallons of air a day? And that over 90% of that is indoors? In fact many of our kids spend less time outdoors than maximum security inmates do.
Should we think more about indoor air quality?
Google PM2.5. Go on. Do it. It’s a really dry thing that really matters to human health, the World Health Organization considers it one of the biggest dangers to human health. It also happens to be really easy to deal with inside your home using your HVAC system.
PM 2.5 stands for Particulate Matter 2.5 microns and below. It’s really small dust. Anything that small gets inhaled directly into your lungs. Below 1 micron it’s even worse, particles that small will go right through your lungs and into your blood.
For example, diesel exhaust contains a lot of particles under 1 micron, and they tend to be heavy metals. Really, really bad news to breathe. If you live within a mile of a large road, you’re probably breathing diesel exhaust right now, even indoors.
Thankfully it’s pretty easy to filter most of that garbage out with a good filter, we recommend MERV 11 or above. HEPA is the highest grade available and is roughly MERV 16.
The problem is most HVAC systems can’t handle the thick (4-5”) media filters needed to do this, and even if they can, many fans use so much energy that it can cost $50-100/month to run the furnace fan (aka air handler) to filter the house 24/7.
But not with BAD ASS HVAC… we consistently see our systems using $1-10/month worth of electricity to run the furnace or air handler fan 24/7. Is it worth that to provide clean air to you and your family? Personally, I finally get to put a BAD ASS system in my own house in the next few months, and I find it totally worth it!
Those are the first two Functions of HVAC. Next time we’ll dig into a few more. A key thing to keep in mind - every car with air conditioning can do five out of 6! Few houses can even do one of them. We’d like to see that change.
Healthy Indoors Magazine publishes these blogs as well, check out my column and the other great info in the magazine.
HVAC 101 - Most of the graphics in the post are from The Home Comfort Book. The 6 Functions is pulled directly from HVAC 101. If you are considering new HVAC, I highly recommend you read HVAC 101, a short 16 page chapter with a bunch of illustrations. If you like that, read Comfort 101. And if you like them both, buy the book.
Want to know something crazy about the deep energy retrofit of this building? It uses 35-45% more energy than one of our much less deep projects. That’s one of the things we learned from the Hiram College TREE House project.
Last time we talked about lessons learned about the dust and dehumidification air quality challenges, the comfort challenges caused by fresh air being introduced without being heated or cooling in the classroom, the second floor overheating because of closed office doors with mini split heads in them, and cooling challenges caused by multi-head mini split heat pumps.
These are all pretty common practices in deep energy retrofits, ones that we challenge with our typical projects. That doesn’t mean either is right or wrong, but the more you understand, the better the job you can do on design on your own projects. In the case of the TREE House, a little more thought into placement of the heads and a larger, higher performance mini split heat pump could have changed the results a lot.
This time we’ll compare two of our projects looking at energy use, insulation, and HVAC.
I already dropped the bombshell, this deep energy retrofit got its butt kicked by a much simpler project. Here’s the 2018 usage for the TREE House, 19,500 kilowatt hours.
Winter looms large as you might expect, January and February are the coldest months here in Cleveland. Note that despite school starting 6 weeks earlier, usage doesn’t tick up until mid-October when the weather turned. This indicates that occupants don’t affect usage much.
1918 House of the Future Project
Now let’s look at the 1918 House of the Future project. You can read much more about both projects in the highly detailed case studies at energysmartohio.com. The 1890 and 1900 case studies are also electrifications, we’re presently working on electrifications 11 and 12 - heat pumps work well even in cold climates.
The usage data for this house is from the Sense energy monitor, check out my YouTube channel for a more detailed look at both of these monitors.
Here’s a high level comparison of the overall projects, then we’ll dig deeper.
Note the drastic difference between energy use. It’s been consistent, the TREE House uses 35-45% more than the 1918 House of the Future despite being only 10% larger and having a far better insulation package on paper. This is pretty wild because no one actually lives at the TREE House, so there is almost no hot water or cooking usage, and lighting usage is presumably lower because it’s needed less during daylight working hours.
Let’s dig deeper into the projects.
The TREE House Insulation Package
I have to say, the insulation package is intense:
During the design charettes for the TREE House, we had advocated against doing exterior insulation, we thought it was too costly for the benefits. I don’t know what it models for this house, but on my old house a $75K exterior insulation job modeled $250/year in savings. That said, the new siding does make the house very attractive, where it used to be rather dumpy looking.
1918 House of the Future Insulation Package
In doing a lot of energy modeling, we’ve noticed that the value of R-value (pun intended) is severely overblown. The 1918 project has ⅓-½ the R-values of the super insulated TREE House, yet still outperforms it substantially.
Why? Heating and cooling (HVAC) is the biggest piece. Let’s look at that.
TREE House HVAC
A boiler was installed for basement floor heat, but it was supposed to be a “kombi” boiler that does both space heat and hot water. Unfortunately the wrong one was installed, so we opted to remove the boiler entirely and replace it with a heat pump water heater. That allowed us to remove the gas meter, our first full electrification - many thanks to Dr. Debbie Kasper for the leap of faith on that one!
Unfortunately, this requires the resistance element in the heat pump water heater to carry much of the load of the house since the heat pump scavenges heat from inside the building, not outside.
If a larger more efficient heat pump had been used and one head was put in the basement, the energy use of the building would probably be similar to the 1918 House of the Future. When the basement is turned into a classroom, the plan is to add another mini split system there.
Here is the usage of the heat pump, represented by the dotted line below the overall usage line. You can see it’s the majority of the usage of the home.
And here is the water heater which heats the basement floor:
It’s difficult to extract the exact energy usage from eGauge energy monitor reports, but these two charts show that HVAC is the predominant energy user.
It should be noted that this mini split heat pump has mediocre performance amongst it’s brethren, better models are in the 10.5-11 HSPF range compared to the 8.5 for this one. It’s only a $1-2K cost difference, so a missed opportunity on a project with a high budget like this one.
1918 House of the Future HVAC
This particular heat pump is also capable of reheat dehumidification, a major part of BAD ASS HVAC. BAD ASS HVAC works for most new and existing homes in most climates, provides excellent comfort and IAQ, and happens to be all electric. I’ll introduce it early next year.
This system also offers whole house filtration to knock contaminants out of the air, something mini splits can’t do well. This particular home did not get fresh air capability though, which can be seen in Foobot air quality monitor reports.
Another nice thing about the Carrier GreenSpeed and its wifi thermostat is that you can track energy use by the day, month, and year, as well as by function - heating, cooling, backup heat, and reheat dehumidification. This house has proven to be a miser, as you can see in this 11/9/19 screenshot.
I have thousands of screen shots watching these heat pumps operate. They are remarkable machines. For reference, our old house used about 12,000 kwh/year PLUS 1800 therms of gas. (1,000 of that was the heat pump water heater, 3,000 was for charging my Chevy Volt.) This house is using 12,400 total without gas!
To me, this is the cool part. $150K demonstration projects are great, but they’re not scalable. This house is worth $200-225K, and this project didn’t add anywhere near the cost to its value. For a homeowner looking to retire someday, this is a poor use of capital.
The good news is that we don’t have to go anywhere near that far to get killer results. In fact, smaller projects can deliver better results, as you’ve seen.
While a $40K project is not inexpensive, it’s less than a typical kitchen remodel. We find that effective projects can be done for $100-200/month or $15-30K, which many households can afford.
More importantly, these projects help solve problems consumers care about like hot and cold rooms, mold, reducing asthma and allergies, and more. Every client has different concerns and budget constraints, and every house has different needs. You have to solve for all three to get a viable project.
Creating viable projects at scale is a serious challenge, frankly one that no one has figured out yet. We’re working on it though, and we think we’re very close. We’ve been developing a system for this called HVAC 2.0, in 2020 we'll be rolling it out and expanding to a nationwide network of HVAC contractors.
In the meantime, I hope this series has helped you to question traditional deep energy retrofits. They have their place and they’ve taught us a lot, but we can get similar, often better, results with much less deep projects that have a real chance at scale.
Caption: dedication of the TREE House 10/24/14
How do deep energy retrofits stack up for comfort, air quality, and energy use? The answers may surprise you.
Back in 2013-2014 we had the opportunity to help with a deep energy retrofit of the TREE House at Hiram College, which is now the environmental studies department.
This was an early project for me, I was winding down our DOE award winning insulation contracting company and just starting to move to the current business model of delivering comprehensive home solutions. This was also before I got comfortable with HVAC. My mentor kept pushing me to argue for a Greenspeed residential split and abandoning the gas meter. But we weren’t really involved in the HVAC design at all Convincing everyone to abandon the gas meter was a big win as that was initially going to stay for basement and domestic hot water.
The house has mini split heat pumps and a heat recovery ventilator (HRV) for fresh air, as well as a heated floor in the basement (which the GC of the project likes to use).
The original walls were dense packed by yours truly, and then 3” polyisocyanurate foam board was wrapped around the building for a total of about R-30. Original windows stayed with an "outie" install. The sketchy foundation was replaced with ICFs rated at a rather questionable R-50. The attic had foam board put down over the old floor, the edges were spray foamed to seal, and then R-60 cellulose was blown on top.
Overall the project was a success, the house is comfortable, has pretty good air quality, and the energy consumption is fairly low. But there were definitely lessons learned. This time we’ll focus on air quality and comfort, next time we’ll talk about energy use and planning/project management.
Air Quality - Dust
Above is a chart from Foobot’s dashboard showing dust (PM2.5) levels at the Tree House. While generally below the 25 micrograms per cubic meter threshold, most of our projects with central duct systems and the fan running continuously stay under 10.
The second chart is from a retrofitted 1960s ranch home with a standard split air source heat pump (it looks like a furnace but without a flue.) Note how the dust levels are flatlined. Ductless heat pumps have no fresh air and poor filtration capabilities, particularly compared to central media filters. That is highlighted by the difference here.
IAQ - Dehumidification Challenge
By measuring with data loggers we’ve found that humidity levels can get above 55F dew point, particularly in spring and fall. Any surface that gets below dew point (usually in basements or inside walls) will condense and can become a mold problem.
Air conditioners remove humidity as they cool, but if there’s no cooling to be done, they don’t run and houses can get unhealthy. We've found that bringing in moisture laden air through an ERV/HRV can make this problem significantly harder to manage.
Humidity wasn’t a major challenge in the Tree House project, a simple 70 pint dehumidifier did the trick. This was in part because the new foundation stopped moisture from coming into the building. We’ve struggled mightily with several older client homes that don’t have a vapor barrier under the basement floor.
Comfort - Fresh Air Issues
A heat recovery ventilator transfers some of the energy from outgoing heated or cooled air to the incoming outdoor air. There can be a problem with this though, when it’s cold outside the air coming out of the registers can be cold. One client measured 45 degree air coming out of his vents when it was 5 degrees outside. Brrrrr.
In the classroom the fresh air vent sits below one corner of the large table. In wintertime students don’t want to sit here because it’s cold.
If this project had a conventional duct system that cold air could have been mixed with the air an HVAC system is moving, tempering the air and avoiding this comfort issue.. With a right-sized, higher end system that runs a lot/continuously, that outdoor air would be heated or cooled before being delivered to the living space.
Comfort - Cold In Summer
The TREE House has a “multi split” heat pump which has 1 outdoor unit and 4 indoor “heads”. Three of the heads are in the faculty offices, the fourth is in the classroom.
A little known issue with multi-splits is that if one head is calling but none of the other ones is, all heads run. The system will push a little heating or cooling to the other heads that aren’t seeing a demand.
Because the front office gets the sun and warms up the most, the AC gets turned on to satisfy this demand. This pushes a little cooling to the back offices that don’t need the cooling making those rooms uncomfortably cold. To make matters worse, the two female faculty members (women typically prefer warmer temps to men) are in these rooms.
Again, a central system would have handled this better by mixing the warmer air in that front room with the rest of the house. In light load situations there might be no call for the compressor to even run. By running the fan in continuous mode the mixing would keep temperatures even. If the temperature difference is pronounced at certain times, the fan speed can be programmed to run at a higher setting to mix better. We’ve used this tactic on several client homes to improve comfort.
Comfort - Too Warm in Summer
Ironically, because the heads are in offices and those doors are usually closed, the conference room and hallway become isolated from the HVAC and often become uncomfortable in summer. Coming up the steps there is usually a 5-10 degree increase in temperature from the first floor on warmer days.
In other homes this issue is often caused by a combination of factors. Poor air sealing in the attic letting hot air into the house, or poor airflow from the AC to the second floor (oversized equipment short cycling). This house has a very tight 985 cfm50 blower door reading, or about 2 ACH50, so leakage isn’t the problem. It’s mainly an airflow problem since there is no airflow from the AC to those spaces. Once again a central system could have helped.
We prefer central systems, in fact we find they’re badass
You may have noticed a bias so far, we prefer central HVAC systems.ll Soon we will be introducing the BAD ASS HVAC system (Big Air Drop Air Source System). Using this one simple system we can provide excellent comfort, air quality, and humidity control. Keep an eye out here!
Insulation and Energy
Next time I’ll dig into the things we learned about insulation on this home, share the actual energy usage of the TREE House, and show how this deep energy retrofit compares to our more basic “comprehensive planning process” projects we’ve done since then.
If you want to learn about beneficial electrification aka #ElectrifyEverything - this is a great place to start. I'll keep updating this list.
Getting Up to Speed
A Practical Guide to Removing Your Gas Meter - My GreenTech article on high/low level views of electrification. Tons of links to further documentation in it. If you only read one thing, this should be it.
Electrify Everything Webinar - An overview of residential electrification aimed at industry pros. What it is, overview of studies, how it should be discussed, what it looks like at ground level and at 30,000 feet, policy suggestions, and more. http://bit.ly/ElectrifyEverythingWebinarbit.ly/ElectrifyEverythingWebinar
Electrify Everything by David Roberts - David coined the term. Great explanation of why it matters.
Electrify Everything Facebook Group - Discussing nuts and bolts. No politics. No climate change. No tribalism. Just doing the work. All are welcome.
Home Comfort 101 - Heat pumps have fairly small outputs, so to get them to work a house has to be reasonably tight. There's a lot of science behind doing that, this is the first chapter of my book and is an entertaining (I hope!) introduction to Building Science and why tighter homes are more comfortable, healthy, long lasting, and efficient.
HVAC 101 - Every HVAC system should be able to do 6 things. Every car can do 5. Most houses can't do any. This is the second chapter of The Home Comfort Book, which is the secret guide to #electrifyeverything.
How Heat Pumps Work and Residential Options - Good intro to heat pumps.
Don’t Heat Pumps Cost More to Run Than Furnaces? - Direct comparison of similar furnace and heat pump heated homes with operating costs to the penny.
Energy Use Intensity Calculator - Until we create value for efficient homes, it will be hard to scale electrification. We're building this calculator on a shoestring based on DOE data, try it out and give us feedback.
Lilli Loves Induction - Our client Lilli was adamantly against induction. Then she tried it. Here's her husband Pete on Twitter talking about it. Induction cooktops are THE key to getting rid of gas meters.
Electrify Everything Store - This will help you narrow down choices, affiliate links so if you buy something, thank you. Induction hot plates, energy monitors, air quality monitors, t-shirts, and more.
Our practice, Energy Smart Home Performance, helps clients solve the roots of problems in their homes. Many end up doing partial or full electrifications. We've removed 7 gas meters and electrified 8 existing homes and 1 new one. Plus a number of hybrids. Here are some of those stories in the most detailed case studies you will find.
1900 House of the Future Case Study - Blue collar client gets "womb-like comfort" with predictable bills. That just happens to be electric.
1918 House of the Future Case Study - Jon Nigro jumped off a high cliff not knowing if his parachute would open. It did, and he stuck the landing. Prettiest case study from energy use perspective.
1890 Habitat for Humanity Retrofit - This project pushed the envelope on multiple fronts, and is an electrification as well. It was featured in the Journal of Light Construction.
1900 TREE House - This project is a Deep Energy Retrofit that now serves as the Environmental Studies department at Hiram College.
Energy Monitor on Hiram College TREE House - The first electrification we helped with. Now the Environmental Studies department.
RMI Building Electrification Study - New homes pencil, retrofits don't.
NEEP Northeastern Regional Assessment of Strategic Electrification - Thorough plan for all market sectors, with residential focus on space heating, water heating, and electric cars. Similar to the 7 Steps to Electrify Everything, it suggests generating renewable electricity, then electrifying end uses.
NREL Electrification Study - Great charts.
National Grid 80x50 Plan - Electrification is one key, no suggestions on how to bring it to market though.
RAP Fuel Switching - Didn't we switch to gas in 1990? Now #electrifyeverything makes sense.
American Gas Association Electrification Study - Consider the source. John Semmelhack's read was that natural gas in US homes is too small of a target, so don't bother with it. Plus it will cost too much and screw up the grid, so don't bother. That said, it's worth a read.
Optimal Decarbonization Pathways for Urban Residential Building Energy Services - University of Texas Austin study 9/18. Using detailed Pecan Street data for Austin, it finds that electrification is critical to decarbonization and found that while HVAC is critical, it doesn't respond well to policy (meaning demand will need to be created directly for it.)
Minnesota's Cleaner Grid - Pathways Toward a Clean, Reliable and Affordable Transportation and Energy System - Dr. Christopher Clack arguably has the most powerful grid model in the world. This study was done for MN, but applies nationally.
Synapse Energy: Decarbonizing the Northeast: It's (Strategically) Electrifying!
EPRI National Electrification Assessment
Articles & Podcasts
How to Buy Clean Electricity in Ohio - I encourage everyone to write a how to for their area using screen shots. This is mine.
Most American homes are still heated with fossil fuels by David Roberts - David tells the story of his own house, which he had a new gas line run to.
Justin Guay’s Electrification Story - Holy cow it was hard.
7 Steps to Electrify Everything - My consumer guide to electrification.
Nate Adams on The Energy Gang - Still crazy this happened.
HVAC School Podcast: Removing Furnaces and Cold Climate Heat Pumps - Bryan Orr questions my sanity. I think I passed. Pretty technical, meant for HVAC audience.
Nate Adams Tesla Model 3 Test Drive - I stayed up until 5 AM in Ann Arbor MI to drive this car. I'm a car guy. It was, well, you have to read it now...
Can Electrification Short Circuite the Utility Death Spiral?
40% by 2030 Residential Scenarios - The math is depressing, the ONLY viable path is substantial electrification. My commentary.
Removed Gas Meters Photo Album - Add yours too!
Tony Seba rEVolution - Seba predicts EVs will replace almost all new car sales by 2025 because of the "S" curve. Why? Growth is not linear when it's founded on demand.
Powering our lives with renewable energy is the future. We can do it if we #ElectrifyEverything!
The only type of renewable energy we are really good at making is electricity. So if we want to use renewables, we need to choose things that run on electricity. We have to #ElectrifyEverything. There's even a lot of a agreement amongst academics about this, and that doesn't happen much!
We have two big energy users in our lives: houses and cars. How do we run them on electricity?
Until recently, electric houses and cars were a sacrifice. Electric stoves weren't great to cook on. Heat pumps didn't work well in cold climates. Electric cars were glorified golf carts. All that has changed in the last few years with things like induction cooking, cold climate heat pumps, and Tesla cars. (The Chevy Bolt and Nissan Leaf are pretty good too.)
Now that there are good electric options for our homes and cars, there is a viable path to #ElectrifyEverything that is not only just as good as using fossil fuels, but often is better. Here are the 7 steps to do it:
Let's dig in to what each step means. Or you can watch the video:
Guest Post from Bob Wells of HVACTraining101.com
Isn’t it annoying that your expensive air conditioner that cost you an arm and a leg is not doing its job properly? It sort of cools the house, but it's still a bit sticky, it runs noisily, and uses a lot of energy while doing so. All this despite being in perfect running condition. If this sounds familiar, it means your AC wasn’t sized correctly to fit your house’s load.
What is “Load” and What Does it Have to Do with Air Conditioning and Heating?
The main function of your HVAC unit is to keep the occupants of your house comfortable. In order to do this effectively, the HVAC system has to match the house’s thermal load, which is a measure of the heat gain and loss for the home. The load consists of two components - the temperature of the air and the moisture content or humidity of the air.
The load of a building is determined by several factors, such as the building construction, air leakage, orientation to the sun and the “R” value of the insulation. The number, size, and placement of rooms and the number, size, and placement of windows and doors play a big role as well. Finally, the types of windows and doors (thermal efficiency); number and arrangement of floors; and the climate are also important considerations.
An AC that is too big will cool down the air very quickly, but it will not run long enough to remove sufficient moisture or “humidity” from the air. This will make the temperature fall sufficiently to make you feel cool, but you’ll also get a clammy feeling. One issue with the insufficient moisture removal resulting from oversized cooling equipment is mold growth. If humidity levels stay too high, mold may take root, possibly in unseen spaces like basements, walls, and crawlspaces. There can be other types of moisture-related damage as well. This is another reason to right size your air conditioner.
Let’s dig into what determines how big your AC needs to be.
Surface area has a large impact on the house load.
The bigger the house, the more AC it will need - but only kind of. It’s an obvious principle but the reality is more complicated.
Many HVAC professionals just use a rule of thumb to guess the load of your house, such as 500 square feet per ton. The rule of thumb method usually leads to oversized equipment. And that often means an increased initial cost and higher monthly utility bills. It also leads to increased maintenance and shortened equipment life because the equipment cycles off and on too frequently.
You should know that a ton in HVAC parlance refers to the rate of cooling, and has nothing to do with the weight of the unit. One ton of cooling is equal to 12,000 Btu/h (British Thermal Units per hour), the rate of cooling required to freeze one ton of ice at 32°F in one day.
When it comes to HVAC, size definitely matters! But it’s not as straightforward as just measuring the square footage of your house. As you’ll see below, there are other factors that go into determining how much cooling (or heating) your house needs.
Here’s a scary thought: the drafts in your home during winter through the windows and under the doors are costing you big money! This is true in the summer as well, but let’s think about winter first because it’s easier to visualize.
When cold air enters through the cracks, it lowers the temperature inside the house and forces the HVAC system to work harder to maintain the temperature at the thermostat set point. The same issue occurs in winter when your AC is running flat out to cope with cool air escaping and moist air coming inside. If you live in a place where the grass stays green without watering it, lots of humidity is sneaking in through those cracks too.
It’s not just doors and windows that are to blame for leaking air. Ducts deliver heated or cooled air to your rooms. But some ducts may excessively leak air or not deliver the right amount of air to each room. This means higher operational costs - from a few percent to over 50%.
The best way to right-size your home’s air conditioning unit is to plug leaks and holes which allow air to leak through. This will immediately decrease the workload on the air conditioner. A licensed HVAC technician can easily identify and seal these leaks in an HVAC system. A Home Performance contractor can seal and insulate the holes in the house itself. An energy auditor can help you find these opportunities as well. In fact Nate recommends beginning with an energy audit to find opportunities rather than just trying something only to be disappointed.
It’s best to be sure your house is sealed tightly. Some flow of outdoor air is important but you don’t want this left to chance. Ventilation is important but should be incorporated into your HVAC system and under the system’s control. But this should be carefully planned so that energy isn’t going to waste.
When you handle a hot pan, you use a dry cloth or oven mitt to prevent burns. The cloth is an insulator – which means it doesn’t conduct heat very well. Similarly, a well-insulated house has layers of materials in the walls and roof to keep the cold in during summer and the heat in during winter. After air sealing, your home should be insulated enough to slow down heat flowing in or out of your home.
Solar LoadThe solar load on your house will determine how much cooling you need in summer and the warmer months as the solar radiation heats up your house. It can also reduce your heating load in the winter by warming up the interior through solar radiation.
The orientation of your house will affect how much sunlight enters your home, raising the air temperature inside. The orientation must be taken into account due to changing solar heat gains throughout the day according to the season. Passive solar building design uses this principle to maximize the amount of solar heat provided to a building in winter, while minimizing it in summer.
The size and positioning of the windows as well as blinds or curtains, impact the sunlight entering your house. Properly-designed awnings and shades can go a long way to reducing your cooling load during hot, sunny days, particularly if you live in a warm climate.
If your house is shaded by trees or nearby buildings, it leads to cooler rooms for part of the day, which is another way to reduce your cooling load. You can enhance the shade on your house by consulting experts from the Society of American Foresters or Extension.org in order to find out what trees work best in your location.
In addition, using light-colored materials on the rooftop will reflect more sunlight, thus preventing heat from seeping in from above.
The climate of the location where you live depends on its latitude, elevation and proximity to the sea. Climate will determine the humidity, temperature highs and lows, number of hot and cold days as well as seasonal variations your AC has to deal with.
In humid climates more energy is required to remove excess moisture from ventilation air. You may notice that the temperature at which you feel comfortable differs with varying levels of humidity. Temperatures as high as 78 or 80F can feel comfortable if humidity is low enough.
The ideal HVAC system is sized so that your AC runs non-stop on the hottest days, as this means it is not oversized. An AC that starts and stops frequently is too big for the thermal load that it is dealing with.
The concept of design temperature comes into play for HVAC design. The 99% design temperature for a house is the outdoor temperature that your location stays above or below for 99% of all the hours in the year, based on a 30-year average. On the other hand, the outdoor air where you live is going to be colder than the 1% design temperature for only 1% of the hours in a year. That happens to be about 88 hours per year.
The cooling requirements of your house will change throughout the day. At night, the outside ambient temperature is lower. This is largely due to solar radiation being absent. Once your thermostat is set to a set point that is comfortable for the occupants, the HVAC needs to ramp up to meet the cooling needs during the high temperatures and ramp down during lower temperatures.
The sizing of the HVAC should take into account the diurnal temperature variation and be sufficient to cool the house to a comfortable temperature at peak temperatures while running continuously.
Occupancy and Use
An interesting factor that you might never think of as affecting the thermal load of your house is you! A person in a room gives off heat, just like any other warm body. We all noticed that on the really hot days (“Don’t touch me - it’s too hot”) and the really cold ones (“Wanna cuddle?”).
The more occupants in a building, the higher the cooling load. However, the number of occupants in a house changes on a daily, weekly and even yearly basis. The load additional load per person is about 400 BTU/hour considering normal residential activity levels.
Think about your average weekly routine. On weekdays, after you are done preparing for work, you are out of the house for around 9 hours. During that time, the house could be empty and thus have a lower cooling load. On weekends, the whole family might be away, leaving the house empty.
With the passage of time, your house’s occupancy will change. Children grow up and leave the house, or guests stay for a few months. While you cannot plan for every eventuality, your AC should be able to cope with at least a reasonable occupancy level. Most calculation methods assume that the number of occupants equals the number of bedrooms plus one.
Designing the perfect sized HVAC system is not as easy as following some rule of thumb. But if you pay attention to some factors such as climate, occupancy, solar load and insulation, you can calculate the optimum system size that will meet your house’s cooling and heating needs for the whole year. A competent HVAC contractor is going to do a lot more than just measure the length and width of your house.
They should run what’s called a “load calculation.” The most common one is called “Manual J”. Insist on getting one and seeing how they calculated. These are far more useful if they do a blower door test to discover how much it leaks, as this can account for 30-70% of heating and cooling load.
When it comes to the comfort of your house, there should be no compromise. But rather than going for an oversized AC like the majority of homeowners, opt for the smart move and right-size your air conditioner. This often saves on initial costs and creates a far more comfortable home.
This is a guest post by Bob Wells, a retired HVAC tech who now dedicates himself to sharing knowledge on his website HVAC Training 101. Bob worked over 30 years in the field, 23 of which he ran his own contracting business. He’s dedicated to keeping up with the latest developments in the field and helping others to learn the trade better and advance their own careers.
Bob is on Twitter with the handle @hvactraining101 and you can also find him on Facebook.
Ever since I read David Robert's article about #ElectrifyEverything, I've wanted to make a T-Shirt.
Roberts talks about how the only consensus for moving to renewable energy and off fossil fuels is to electrify everything: houses, cars, trucks, planes, factories, etc.
All of those are looking possible (even planes!) Our specialty is houses. We've removed 5 gas meters so far with 3 more coming in the next few months.
We want #ElectrifyEverything to become a slogan. So I put together a T-Shirt you can order. Or a hoodie. They are print on demand, so they're not particularly cheap. (I make $5-7 each, full disclosure.) Thanks to my talented wife Rachel Adkins for designing it. I chose decent quality shirts and hoodies.
I'm really just messing around with this, so I'll likely take this post down in a few months. If you want one, get it now.
If you want to make one for your own brand, the file is below.
Want one? Order one. Any color you want as long as it's black.
Fair warning, the payment service I use does not send shipping notifications.
If you don't have it in 3 weeks, reach out. Kindly don't bug me until then. (firstname.lastname@example.org) Mine came in 11 days.
Want to make your own #ElectrifyEverything T-Shirts?
Let's make #ElectrifyEverything a movement!
Here's the #ElectrifyEverything file if you want to customize it with your own brand. It's a hi-res print ready Photoshop file. I'm giving permission for reuse with modification. You could use Printful.com like I did. Like I said, this is an experiment.
You're not alone if you're asking what the average gas and electric bill is in the US.
The simple answer is about $2000/year or $165/month. The Department of Energy has the lovely chart above.
What you really want to know is more complex.
The odds are, the $2000 average gas and electric bill is unsatisfying. What you really want to know is how do the utility bills at your home compare to your neighbors.
The Department of Energy is also helpful here, they collected energy use from 9,000 homes nationwide and put them in the Building Performance Database.
The trouble is, you can't search the database.
Good news! We developed a calculator based on the Building Performance Database where all you need to put in are your zip code, square footage, and annual utility usage to be able to see how your home stacks up against similar homes in your climate zone.
Climate zones are other parts of the country that have similar winters and summers to you. Since the Building Performance Database is relatively small, using climate zones helps smooth out any states that don't have a lot of gas and electric utility bills reported. Here are the US and Canada climate zones.
How does your home stack up?
Our calculator tells you the EUI, or Energy Use Intensity of your home, and compares it to other similar sized homes in your climate zone.
Energy Use Intensity is a complicated sounding phrase for a simple thing: how much energy does your home use per year, per square foot? It's a metric we're big fans of, in fact I wrote an article for GreenTech Media about EUI in 2016. This calculator grew out of that article.
0 EUI means your home uses no energy, or you produce all the energy you use with solar panels or the like. Higher is worse. Where I live in Cleveland, 100 is a bad EUI. For milder climates like Florida, 50 might be bad.
When you enter your email at the bottom of the calculator, you'll get a report that shows how your home stacks up on three factors: overall usage, electric usage, and gas (heating) usage.
Sample Report from the EUI Calculator:
Curious? Try it out!
For now, you can just throw some numbers in and see what comes back. We give you suggestions.
If you want an accurate and complete report, grab a recent gas and electric bill, and look for the annual usage. You'll get a simple report when you click submit. To get the detailed results I showed above, you'll need to enter your email in the second step, after you click submit.
Soon you'll know how your home compares to others! Comment below what EUI you got!
PS If you enter in your utility costs, you can find out how much more (or less) your energy bills are than your neighbors. Our calculator can also show what your home would be worth if efficiency was valued at time of sale.
Energy Use Intensity Calculator
See how your energy bills compare to others in the Building Performance Database.
If you haven’t seen it, there is a Tesla Model 3 driving around the country right now, driven by one of the first non-employee owners, You You Xue. Check out the Facebook page of the Tesla Model 3 Road Trip to see if there are any remaining stops near you.
I traveled to Ann Arbor Michigan to see it Friday, the closest stop to my house. This is an unbelievably generous thing for You You (sounds close to yo-yo) to do. Be sure to thank him. He’s beating the tar out of his car, putting a ton of miles on it, and enduring a lot of sleepless nights for little to no personal gain.
Let’s start with full disclosure. I have a first day deposit down on a Model 3. I do not own Tesla stock (unless it’s in one of our mutual funds.) While I’m a big fan of Elon Musk, I am not a total fanboy, I’m more than willing to be critical.
Problems with the Model 3
Speaking of being critical, let’s start with the problems with the car either You You or myself noticed. Almost all of them are software based, which means that Tesla can push an Over the Air Update to fix them. Most were related to the record breaking cold snap You You was driving through.
1. Fogging glass in cold weather. There was ice inside the back windows. The HVAC system in the car couldn’t completely clear the fog. You You said he couldn’t get it to completely clear. I tried a few things as well and didn’t get anywhere. There may not be enough outside air coming in to dry out the interior or enough dehumidification capability at these low temps. This is something that will need to be addressed by Tesla, it reduced visibility out of the car significantly. It’s also the only serious flaw I experienced.
2. Poor trip calculations in cold weather. Cold weather below about 10F is really hard on batteries and electric cars in general. Cars only get about half the range and charge at slower speeds. You You almost got stranded just before he got to Ann Arbor, I watched this harrowing video live in my hotel room, he pulled in with 0 km showing on the range meter, and drove for a few minutes with it on 0. He was less than pleased about it (language warning at the end of the video.)
3. “Ping Pong” in Autopilot. AutoPilot 2.5 is still a touch rough compared to 1.0. It bounces around in the lane sometimes. Here’s a video of the test drive where we got on the highway and engaged AutoPilot. Ping ponging is not super obvious on video. It also doesn’t seem completely fair to whine about small imperfections of a car literally driving itself. This will get ironed out over time, and part of the ping pong was a dotted line on the side of the road where an exit was. It does better with solid lines. Using AutoPilot on snowy days where road markings have been obscured is not a great idea.
There were a few other things You You mentioned like navigation being glitchy and some glitches with the screen like there being no way to exit the “Paint” app where you can draw on the screen. All of them can be solved with updates, and since updates don’t require a trip to the dealer, I’m not concerned.
My Car Cred
I should probably start with a little car cred on my part. I grew up around expensive ($250K+) 1920s and 1930s cars being restored by my dad. I’ve rebuilt 3 engines (only one of which blew up…) I’ve driven more cars that I can count from a Ferrari Testarossa to a Mercedes S600 to one of the Queen's Rolls Royce Phantom 5 limos to my wife’s first car, a rusty 1992 Toyota Corolla. I four wheel drifted my 1989 Ford Thunderbird Super Coupe through college, scaring the bejeebers out of my friends. (That car is still in one piece, but it’s the engine I blew up.) While I may not be the most skilled driver, I’m no slouch.
Basically, I’m a car guy. I decided a few years back that I’m done with internal combustion. The path to the future is to electrify everything, something that we do to houses in our Cleveland Ohio practice.
As far as EVs, I’ve driven a Nissan Leaf, a Chevy Bolt, and a Tesla Model S P100D Ludicrous. I found the Leaf and Bolt to be quite vanilla and uninspiring. The P100D is a stupidly fast car, but it costs more than my house and I don’t prefer big cars anyway. I’ve always wanted a BMW M3, I’ll likely get a different kind of M3 now…
Driving Impressions of the Model 3
Thankfully, car magazines have already gushed about this car. Motor Trend’s Kim Reynolds said “Have I ever driven a more startling small sedan? I haven’t.”
I agree. This is not just a great EV, it’s a great car. The Chevy Bolt felt like a $22K car that costs $40K. The Model 3 feels like a $70K car that costs $35K. (Or $55K in the case of You You’s car.) I think the base car would suit me fine, which was a pleasant finding for my pocketbook.
The Model 3 reminds me of a mild mannered brother of a mid 90’s BMW M3 I drove. It has a very firm, but not punishing ride. The steering is laser precise like the Bimmer or my 2006 Saabaru with Subaru WRX steering. I loved it. You can even make the steering lighter if you want with the touch of a button.
It’s very quick. You You encouraged us to hammer the car, I did and let off at 75 MPH. My gut is it took 7-8 seconds with 4 adults aboard on salt slick roads in snow tires.
It’s sure-footed. With snow tires You You said all wheel drive is not necessary. I didn’t drive it in the snow, but the car is unusually sure footed on salt encrusted roads. I got in my car after the test drive and spun the wheels like crazy with the same driving aggression.
It was only a 10 minute test drive, but where the Leaf and Bolt felt very vanilla, this car felt like it was built to be driven hard. It almost begs to be beaten on.
The interior is sweet. I’ve never seen such a simple interior, almost devoid of buttons. The steering wheel feels a bit cheap, but all the rest of the materials in the car feel expensive and nice to the touch. The wood on the dash is better than I expected. The buttons to open the doors have a great tactile feel. The doors close with a satisfyingly solid clunk. The Drive noted no squeaks and rattles in a record breaking cross country trip, that was my impression too.
The HVAC, aside from the defrosting problem, is remarkable. I love how you can aim the airflow anywhere you want. The single vent slit and lack of other vents is part of why the interior is so striking. I only scratched the surface of how to configure the HVAC system, but it’s one of the slickest setups I’ve seen.
Being an energy guy, I had my Flir One infrared camera with me and I clocked the back seat vents at around 135F. For reference, most home furnaces put out air from the vents in the 105-120F range. My camera is not super trustworthy for temperature readings, but this felt about right, the air coming out of the vents was hot. The car has no problems keeping warm, even in frigid temps. If, that is, you have the range to run the heat that hard, a challenge unique to EVs.
The backseat is cavernous. I’m 5’8”, so no giant, but I had 6” in front of my knees and the front seat was set for You You, who is around 6’. The back seat made me think of a 7 series BMW for legroom. The glass roof made the car feel open and I had 4-6” above my head as well. The space is really well utilized inside the car. I wouldn’t want 3 people in the back seat, but for two it is quite comfortable.
If you are on the fence about buying a Tesla Model 3, just do it.
I can’t thank You You Xue enough for doing this crazy trip, which he has done largely solo. I was particularly impressed with him, he’s self confident and wildly organized. He bears up well under challenges like his car almost dying a few hours before he arrived and two severely bent wheel rims just after he left Ann Arbor. He’s young, still studying, and I got the impression that I’d met a great man just about to start his career.
He’s also not a Tesla fanboy, even though he has 3 Teslas. (An S, 3, and X, I can’t help putting them in that order.) He was quite critical of Tesla at times, talking about how some of the programming issues in the screen were elementary and being pretty fierce about the range calculator in cold weather. He’s been quite open about his experience with the car on the Tesla Model 3 Road Trip Facebook page, if you want to know about the car, warts and all, be sure to read the whole page.
Oh, and don’t ask questions that are already answered on the FB page. He will simply point you to the page to look for the answer.
You You was originally scheduled to get to Ann Arbor at 5 PM. He arrived at 3:40 AM the next day. The experience of meeting him, seeing the car, and then driving it was totally worth it!
I also hope he enjoys the signed copy of The Home Comfort Book I gave him, which just below the surface is about how to electrify your home.
Thanks for reading! And good luck to you as you #electrifyeverything!
If your electricity bills seem too high, and you aren't sure why, getting a home energy monitor could be a good way to figure it out. If you want to know if your usage is high, use our calculator that compares your home to others in your state based on Department of Energy data.
In our practice we've used three different energy monitoring systems. More importantly, we've used them all for over a year, so we understand their strengths and weaknesses.
Two recent entries are the Curb and the Sense, which offer more modern looking apps than "older" electricity monitors like eGauge 3000 at the Hiram College Tree House project. (You can see what's happening at the Tree House live here.)
Let's dive into the comparison of the three, here's my video comparison of the three energy monitors (which is more in depth than this article):
Full Disclosure: Curb sent me two of their monitors for free and paid to install them. I bought and installed Sense myself (they recommend having an electrician do it.) The eGauge 3000 was bought and installed by Hiram College, my role was in fixing the setup so it created useful data.
Energy Monitor Framework
When comparing products with very different strengths and weaknesses, I find it's best to look for the attributes I care about. For power monitors here are 5 attributes I find useful. Next we'll dig into how the attributes apply to each monitor.
Ease of Install
There are two types of home electricity monitors, which one you choose basically determines install time:
Installing machine learning energy monitors is no big deal. If I did it every day, I bet I could do it in 15 minutes, my two installs each took about 25. While the manufacturers recommend having an electrician do it, for DIYers that aren't nervous around their electric boxes, it's not a big deal. (Be sure to turn the power off!)
One bad part of machine learning energy monitors is that you never really know if a device will be monitored. Sense doesn't seem to pick up individual appliances under 30 watts. If you want to know when your cell phone charger is on, you're probably out of luck.
Another bad part is that machine learning devices often confuse appliances. My Sense thinks that my coffee maker is my dishwasher, and vice versa. It also thinks my heat pump water heater is my dehumidifier, and vice versa. If two devices look similar, the Sense Labs device may get confused. Fair warning.
Multiple circuit electricity usage monitors, on the other hand, will let you know if something is on, as long as you choose to monitor that circuit. It won't tell you what specific appliance is on, but you will likely be able to tell by how many watts it pulls. In the case of a dishwasher or refrigerator, which are supposed to have dedicated circuits, you will know for sure when they are running.
A big downside to multiple circuit devices like Curb and eGauge is that they are a serious pain to install well. Every circuit in your house has to be labeled, and often they aren't. It took me over 2 hours to figure out the 40+ circuits in my house. In one install, the circuits were mislabeled, so after spending 4 hours carefully installing a Curb, I had to go back and totally change the configuration, which took me another 3 hours, plus the time it took to figure out what the correct circuits actually were. (I would get faster with time, but the 45 minutes that Curb mentions is unrealistic in anything other than ideal conditions.)
Plan on installing multiple circuit monitors twice. Once with the best information you have, and again when you have a better handle on which circuit goes where. Since you are limited in how many circuits you can monitor, you'll likely change which circuits you monitor the second time if you see the "other" category with huge power usage.
While the install time of multiple circuit devices may seem off-putting, with machine learning devices you will spend a fair amount of time figuring out which appliance is which. Sense will tell you that "Unknown Motor 6" just turned on, it's your job to figure out what that motor is. So machine learning devices can be heavy on after install work, where multiple circuit devices are a lot of work to set up.
Is the Machine Learning type or the Multiple Circuit type better? It depends on what you need and your preferences are. If you absolutely, positively have to know what that big draw is, get a multiple circuit device. If you are ok with the potential that a machine learning device won't find some appliances, you want a quick install, and you don't mind a little detective work figuring out what "Unknown Motor 6" is, get a Sense or Neurio.
The software really makes or breaks electricity usage monitors. Depending on your preference, you may want a web app, a mobile app, or both. The video does a far better job dealing with this than I can in words, so take a look at that section of the video. The last 3 attributes relate directly to the software/apps.
The quick rundown is that Sense has hands down the best app, but it's a mobile app only and you can't export data from it. eGauge only has a web app, it's a bit old-school, but provides the best data download. Curb has mobile and web apps that function similarly, and is really good at charting usage by circuit.
Odometer vs. Speedometer
In your car, the odometer tells you how many miles you've driven, but not how fast you went to drive those miles. In a home energy monitor, this is how much energy you have used over time. Sense and Curb will tell you how much energy individual appliances/circuits used. Sense will tell you almost any time period you want, Curb only tells you week by week in their weekly "energy audit" email.
In your car, the speedometer tells you how fast you are going at any given moment. In home energy monitors, they tell you how many watts you are using at any given moment, and also chart how many watts were being used at different points in time. All three tested monitors will tell you how many watts were being used at a certain moment by individual appliance or circuit.
The Sense stands head an shoulders above the Curb and eGauge 3000 for odometer and speedometer functions, in my opinion.
For the speedometer function, Sense lets you quickly zoom in and out on usage at any moment since the device was installed.
eGauge lets you do it by setting the time parameter, but that's much slower.
Curb has an awesome chart for which circuit was using how much power, but you can only choose time periods of 3 hour, 1 day, 1 week, 1 month, 1 year, and all. If you want to zoom into 3 hours yesterday you're out of luck.
For the odometer function, Sense lets you look at the total usage of any day, week, or month. (See the app review video, it's pretty cool.) It also breaks it down by the appliances it has found.
Curb is quite limited in that the only usage data over time comes from the weekly audit emails, hopefully that will change. Curb does break usage down by circuit in that email, though.
eGauge has a pretty decent odometer function that lets you select any time period to look at usage, and by default shows you the last month of usage. It does not break down usage by circuit unless you export the data, which is our next topic.
If you really want to crunch the numbers, you need to export data into a spreadsheet and go nuts. Personally, I don't really like manipulating spreadsheets with lots of data, I prefer visual representations of data to look for anomalies.
eGauge wins this category hands down. You can export data from any period, and you get usage by circuit. It's awesome.
Curb lets you export data for its set time periods (3 hours, 1 day, 1 week, 1 month, 1 year, and all.)
Sense fails in this regard. There is no data export as I write this in October 2017. They plan to do it, though.
It's up to you to decide if this is a big deal.
This is a particularly sticky issue. CT clamps are very sensitive about how they are installed. If you put one on "upside down" it won't report that a circuit is using energy, it will report that it is generating energy. That's what I mean by reverse polarities. If you ever got your pluses and minuses backwards in math, you know that it makes your answers wrong.
This only appears to be a problem with multiple circuit devices. If you put a CT clamp on backwards for Sense, the software compensates.
For the multiple circuit monitors, it can ruin the usefulness of the data. At the Tree House, enough were reversed to essentially zero out the energy usage of the building. The eGauge said it had used 350 kilowatt hours (kWh) for a year, when reality was a little under 15,000. I've struggled with my Curb to get it accurate.
Curb and eGauge both give you ways to reverse the polarities of the circuits, but it's an extra step.
Curb made it more difficult to reverse polarities with a recent update, and now I have to classify circuits like they are generating electricity rather than using it to reverse them. It's less than ideal.
Avoiding the reverse polarity problem is another reason I lean towards the Machine Learning variety unless you are an advanced user.
Having a year+ with each of these three home energy monitors has been really useful to understanding their strengths and weaknesses. Professionally, we use them to figure out if our assumptions and energy use predictions were accurate, and to find problems in client homes.
As a homeowner, it's a step to finding out why your usage is so high. (You can use our calculator, which is based on Department of Energy Data, to see if your house is an energy hog or not.) You might also look at which months are highest to figure out what might be causing the bills, or hire an energy auditor to help you.
Free Comparison Chart
Ready to Buy?
If you decide to buy one of these devices, kindly use these links, we get a small cut and it helps pay for producing content like this. Thanks for reading, and if you found this useful, please comment and share!
Nate Adams is fiercely determined to get feedback on every project to learn more about what works and what doesn't. This blog shows that learning process.