HVAC and the Corona Virus
I’m writing this part of BAD ASS HVAC as the COVID 19 corona virus is shutting things down. Flights to Europe were just suspended. Classes at Ohio universities were moved to being 100% remote a few days ago. The stock market is plummeting. Ohio schools were just shut down for 3 weeks. Preventing the collapse of the medical system is a clear and present danger, as we’re seeing in Italy right now.
While covering our mouths during coughing, handwashing, avoiding touching our faces, cleaning surfaces, and avoiding large gatherings seem to be the biggest factors in slowing the spread of the virus, it strikes me that HVAC could use some more attention.
This chart from ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) shows how important humidity is for a number of health factors. Note how keeping relative humidity between 30-60% reduces the propagation of both viruses and bacteria.
A historical note, we’ve seen something like this before. The Spanish Flu of 1918-1919 drastically changed how boilers were sized. Instead of being sized to heat a home under normal conditions, they were sized to heat a home in winter with the windows open. The idea was that fresh air and sunlight would reduce the spread of the virus. As important as humidity control seems to be, that much dry cold air is probably not advisable, but some fresh air seems like a safe bet. This article will focus on fresh air and its relationship to indoor air quality.
Hopefully you’ve heard this from me before; we breathe 3000 gallons of air per day. Since we spend 90% or more of our time indoors, most of that air goes through an HVAC system. Without overselling the benefits, there are a few ways HVAC can help reduce viral spread:
These are all things that BAD ASS HVAC does.
Humans Suck at Long Term Thinking - Plant a Seed Now
While we all have corona virus on our minds right now, that’s really only one piece of creating healthy environments. A good HVAC system also helps with reducing particulate pollution, chemical pollutants, mold, dust mites, asthma, and much more.
The curse is, adding all the capabilities that BAD ASS HVAC offers is really only easily possible (and cost effective) at equipment replacement time.
We humans excel at dealing with clear and present danger, as we’re seeing with the response to COVID 19, but that’s going to be temporary. In a few months or years, our memories will be fading about it. As humans we suck at dealing with things that have a long time horizon like investing for retirement, the health effects of excess weight, or in this case spending a little extra on a new HVAC system to equip it to have BAD ASS capabilities.
So before we dig in, you might mentally plant a seed to ask for a BAD ASS system when you buy new HVAC, so the next time we have a wildfire or pandemic you’ll already have the system in place. All you will need to do is turn up the fan speed to increase filtration and fresh air, then adjust humidity settings.
OK, enough about corona virus, let’s get to talking about fresh air, the 4th function of HVAC!
The 6 Functions of HVAC
These are the 6 functions of HVAC, every HVAC system should be able to do them. All cars with air conditioning can do 5 of 6, most homes can’t do any. We discussed load matching in part 1, filtration, and dehumidification in part 2.
This time we’ll talk about fresh air.
Fresh Air - What is it and do we need it?
You might have heard that “houses need to breathe”. Nope, not true. People need to breathe, as do pets and very importantly combustion appliances like furnaces, water heaters that use a fuel, gas stoves, and gas dryers.
I should mention that houses do need to stay dry though, which we discussed last time with dehumidification. All sorts of bad things happen when houses get too damp (or dry!) as you saw in the ASHRAE chart above.
Making your home tighter increases your ability to control your indoor environment without regard to what is happening outside.
As we make houses tighter to get better control over heat, air, and moisture flowing in and out of them to provide better comfort, it’s important to bring in some outdoor air so the air inside doesn’t get stale or unhealthy. Fresh air is also known as “mechanical ventilation” in the HVAC world.
What does stale air look like? One of the common proxies is carbon dioxide. For more about proxies for healthy air see To Catch a Health Thief from the May 2018 edition of Healthy Indoors Magazine.
Carbon Dioxide Makes You Dumber
Lawrence Berkeley National Labs found that even modestly high levels hurt our brain function. Atmospheric levels are about 400-500 parts per million (ppm) of CO2. At 1000 ppm effects were seen, at 2500 ppm cognitive functions fall off a cliff.
2500 ppm might sound high, but if you sleep in a closed door room with your spouse/significant other, you’re probably hitting at least 1500, and 2500 is possible.
If you have a boiler without forced air, you’re almost certainly breaking 1500 ppm at night (those open windows during Spanish Flu times helped with this.)
If you have forced air and it runs a lot, those levels are likely lower because they are being mixed throughout the house and evened out. Sadly, most systems are drastically oversized, so it may not run enough to drop those levels. Could your sleep be improved by lowering CO2 levels in your bedroom?
A CO2 anecdote. We have a client whose teenage son competed nationally to solve Rubik’s cubes. He started going outside for a few minutes before competing, and saw a noticeable drop in his solve times. I thought that was wild.
Ideally we want to keep CO2 levels low, a realistic level is in the 600-800 ppm range indoors.
How Much Does It Take to Keep CO2 Levels Low?
This is geeky, but bear with me a moment. There is an international standard for fresh air in residential homes called ASHRAE 62.2. 62.2 is partly based on research from a few homes in the 1980s using expensive monitors (one of our clients was part of the study in fact.) It’s also partly based on educated guesses which has lead to some vigorous debate.
62.2 works out to 30-100 cubic feet per minute (cfm) for most homes, depending on the house size and number of occupants. For reference a standard builder grade bath fan is rated at 50 cfm, although they usually flow less than half that because of poor install practices.
The trouble is, getting above 30 cfm pretty much requires a separate piece of HVAC. This can easily add thousands to the cost of your HVAC system, and adds another fairly major piece of equipment to maintain, and eventually replace.
My friend John Lapotaire, an air quality consultant in Florida, did a small study of 21 Florida homes 7 years old or newer with ERV or HRV fresh air systems (energy recovery ventilators or heat recovery ventilators). 19 of those 21 systems had failed, primarily due to the filters not being changed and the motors burning up. None of those homeowners was aware of the failure.
Hearing that, and also armed with 40 $200 indoor air quality monitors, I wanted to see just how much fresh air really was required to keep CO2 levels reasonably low. Where $50,000 or more of sensors in a trailer parked in the driveway was once needed, technological advances allow us to monitor important home IAQ metrics for a few hundred dollars.
For a few hundred dollars we can get a decent idea of what’s going on (no more guessing), and not just temporarily.
Spoiler: it looks like MUCH less than 62.2 ventilation standard is needed for most homes.
This is not hard and fast, but the good news is it allows for us to use a much simpler fresh air system which I’ll lay out in detail in a coming article. Let’s look at a specific example.
35 People In One House
In February of 2019 one of our clients, Hallie Bowie, was kind enough to host an “Electrify Everything” event in her home to show how an all electric home is totally possible in cold climates. Her electric home looks remarkably like other homes of it's vintage, and comes with far better average comfort. Hallie noted to me during a cold snap last winter that this is the first house where she has no idea what the temperature outdoors is without stepping outside. (That’s thanks to “load matching” and keeping surface temperatures nice and even, as discussed in part 1. I digress.)
Let’s look at some data. Most tVOC sensors are cross sensitive to CO2, the one in Foobot is. If you have some idea of what’s going on in a house like cleaning, cooking, or lots of people, you can infer what’s being picked up. In this case I’m pretty sure it’s CO2 from a bunch of people breathing since there were 35 people in the house.
Some notes on the house. It has a very simple fresh air system that I turned up to 30 cfm during the event. It got warm enough inside from all the people that we cracked the sliding door for about an hour, but it was closed by 7 PM.
The chart below is tVOCs aka total volatile organic compounds or chemical pollutants as the event began at 5 PM.
Again, these are tVOC levels, so I’m not 100% sure what the precise CO2 levels are, but suffice it to say they got way above the 600-800 ppm target. This next chart shows the peak at 6:30 PM as we broke up to go look at the HVAC in the basement and moved away from the Foobot monitor. Shortly thereafter the event ended and people began going home.
This next chart shows that by 2:15 AM, almost 8 hours after the peak, 30 cfm of fresh air (less than half the 62.2 recommended level for this home), tVOC levels were back to normal, which indicates CO2 levels were back to normal as well.
This is a good example because it’s such an extreme event. We hear people size HVAC systems for parties like this, which is frankly silly because it’s a couple of hours per year, and as you can see if the HVAC system is done well, the spikes don’t last that long.
We’ve seen similar results in the other client homes we monitor. They do need some fresh air as we get them tighter, but not an incredible amount. Don’t take my word for it though, go measure yourself!
In our projects and monitoring, we’ve found that 10-30 cfm of “fresh air” aka mechanical ventilation has been adequate to keep carbon dioxide levels moderate and air quality good, at least through the proxy measurements we’re using. This supports what Joe Lstiburek of Building Science Corporation found during the Canadian R2000 program which built tight homes and used a similar fresh air strategy to BAD ASS HVAC.
Two caveats going back to how people and combustion appliances need to breathe. First if there are more than 3-4 people living in a home, more fresh air will be needed. Second if you have a “natural draft” water heater or furnace that pulls air to burn from inside your home, it will need additional air too. Since we only install heat pumps or furnaces that draw combustion air from outdoors, this is not a large factor in our projects, and is also an argument to get rid of natural draft appliances.
Fresh Air Ain’t Fresh
One last thing, fresh air often ain’t fresh.
Check out the dark corner on this filter of a client HVAC system. This is where the outdoor air stream hits this filter (it’s from a ventilating dehumidifier, which is how we keep this particular home dry and healthy, more in Part 2 of this series.)
This client home is about 1000 feet from a Cleveland highway. This filter was only 6 weeks old in this photo, which shocked me. I don’t know for a fact, but the odds are high that most of that dark stuff is small particles from diesel and car engine exhaust, likely mixed with some brake dust. If you live near a large road, you’re breathing some of this too.
This highlights the importance of filtering “fresh” air from outdoors. It’s automatically built into the BAD ASS HVAC system. More on filtration in part 1 of this series.
The other important application here is during wildfires - you want to have a really good filter on your home HVAC to knock most of the garbage out of the air. I personally live in a rural area, most of my neighbors burn wood, and I look forward to installing BAD ASS HVAC in my house later this year so I can stop smelling wood smoke while knowing how bad it is to breathe.
Tune In Next Time!
And there you have it. Fresh air is very important to having a healthy home, but we might not need as much as we think. Also, it should get filtered through a MERV 11 or higher filter before being put into the house.
Next time we’ll wrap up the 6 Functions of HVAC by discussing how mixing helps improve comfort and air quality as well as digging into humidification. Then we’ll dig into the BAD ASS HVAC system itself!
Stay safe out there!
PS If you'd like more details, here's a video walking through the BAD ASS HVAC system. The system itself is quite simple, but this video is made for an HVAC contractor audience, so it's a bit technical. Soon I'll record a video at a homeowner level.
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.