Ventilation System for Ranch-Style House
I just wanted to share a simple ventilation system that is working very well for our ranch house. Our house is 28×48, on a conditioned crawl space, completed 1 year ago in the mountains of Virginia. Good insulation levels, and air sealed to 1.6 ACH50. We have a large open room at the east end, with a mini split and an air intake fan nearby.
The opposite west end of the house has two bedrooms, with floor vents in the far corners open to the crawl space. Our conditioned crawl space has an exhaust fan located back at the east end. We have a hallway going down the center of our house to the two bedrooms. Our mini split blows conditioned air through the great room and straight down the hallway.
So the ventilation in our house comes in at the east end, and is pushed down the hall toward the bedrooms at the west end. The air then goes down both open floor vents in our bedrooms, and is pulled across the length of the crawl space and out the exhaust back at the east end.
This setup is providing fresh air throughout the length of our house, and into our bedrooms even when the doors are closed. After a full night with a closed door, the CO2 is still below 800.
I think I might find a way to attach a timer to both the intake and exhaust fans, to run the fans for shorter periods each hour. Right now, the minimum ventilation possible is 80 CFM with our system, which is a bit much for our 1,300 sq ft house. I think as long as I can keep the CO2 below 1,000 ppm, I’ll be happy.
A lower CFM will save on energy and slightly reduce the humidity levels in the summertime. We have to run a dehumidifier in our great room in the summer, as our outdoor temps are often too low to need much air conditioning, and we are in a humid climate.
We designed our house to be mostly duct free, and are generally pretty satisfied with how things are working. I thought I’d share this concept. Also, this setup works as a radon control system, too.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
That's a good foresight Debra, Thanks for sharing!
Debra,
It soulds like a well thought through solution - which throws the typical set-up of supplying air to the bedrooms on its head.
- Do you rely on the ventilation system to bring warm air into the bedrooms, or do you have supplemental heat there?
- Is the supply air cold in the living room, or does the nearby mini-split condition it sufficiently?
The combination of the ventilation system and the mini split blower aiming straight down our hallway toward the bedrooms provides adequate heat most of the time. Due to budget constraints, we self-installed a 1.5 ton Mr. Cool mini split, which doesn't provide adequate heat when temps drop much below 20-25 F for long. So we do have supplemental baseboard heaters in most rooms. I don't use mine much, but my sister feels the cold more, so she sets her bedroom thermostat a bit warmer. A quality mini split would probably supply most of our heat all winter long.
The air conditioning during hot weather doesn't fully condition our bedrooms. Our bedrooms are warmer in the summer than I would like. I prefer to sleep in cool temps, but our bedrooms rarely get much above 73-75 in the summer. I often leave my bedroom door open in the summer to try to encourage my bedroom to cool down more with the mini split AC.
I can't say I've ever noticed a cold draft from our supply air in the winter. But it comes in near the ceiling level, about 4 feet from mini split and I think it gets sucked in and conditioned before we can feel anything.
I think my biggest frustration is the difficulty in controlling humidity levels. We don't need air conditioning enough for the mini split to adequately reduce the humidity levels. Twenty years ago, it wouldn't have been a problem here, as our summer dew points were usually near 60-64. But with climate change, we're now getting dew points 67-72 for weeks or months on end. So we use a noisy dehumidifier in our great room. Ugh! And in the winter, our house air is frequently 20-30% RH. I get nosebleeds from it.
I think this is a good solution in warmer climates.
Around me with 7200 HDD, 80CFM of air with no heat exchange is about the same energy loss in a season as through 2000sqft of 2x6 wall. The cost of that does add up over time.
Good point! With my milder climate, an energy specialist here in Virginia calculated that many homes would not save enough energy to pay for an HRV/ERV. But I would like to see if I can experiment with getting my ventilation down to 50 or 60 CFM and see how my CO2 levels are.
Akos,
Heat recovery aside, I like path the air follows in Debra's place. It's not something I've seen or though of doing.
You can run heat recovery with this type of setup without too much problem.
Install the ERV in the crawl, pulling the stale air from there and have it supply the fresh air to the living room above the wall mount mini split head. Not too much ducting, the cost of a budget ERV is probably comparable to the cost of the two fans and much better efficiency to boot.
Akos,
I think that would work well in our climate.
Debra, I appreciate the KISS rule which you are highlighting in your setup. It's not an option for us in the cold zones, but I appreciate the cross flow setup. Pulling the exhaust air via floor vents/crawl space makes good sense. It's even better if you pull the intake from the high pressure side of your house based on prevailing winds.
"And in the winter, our house air is frequently 20-30% RH. I get nosebleeds from it."
You mention humidity concerns in both summer and winter, and this at least would be moderated with an ERV. You also mention that you're running a dehumidifier a lot in summer, which is a losing battle if you're pulling in a lot of humid air. Conversely in winter with humidity at 20-30%, you are pulling in dry air and fighting that.
How much does it cost to run that dehumidifier in summer? Your energy analysis likely did not factor that in.
After staring at my instrumented test setup here for the last month, I've been surprised by how much water is collected by the HRV (taken out of the outgoing air stream) which would otherwise be redirected back (at least in part) into the conditioned air stream by an ERV. I understand that an ERV at this point would throw a wrench into your cross flow ventilation setup, but it would for sure help moderate (not fix) your humidity challenges.
With regard to high efficiency ventilation fans that can be speed controlled, I've been messing with 3-4 of these (quiet EC fans with 0-10V speed control) with automation and can provide a few pointers if you're interested. For winter humidity, providing the temps are above freezing, you could always just add an inline humidifier along the lines of the AprilAir 500 series to your intake.
Dennis, I would love to learn more about the ventilation fan options you've mentioned. Also, is it possible to tie them into a CO2 monitor? I'm hoping that I can find a way to minimize our ventilation enough to reduce our humidity issues while still maintaining air quality. It doesn't make sense to ventilate any more than we really need, or when we are away from our home.
As for winter humidity, it doesn't get bad until the temps drop below freezing, so that inline humidifier may not work for us.
Actually, it would be possible to install an ERV and still maintain the air flow through the house and crawl space. I would just put in a short duct to exhaust the crawl air out through the ERV, which could be located where the air intake fan currently is inside the front hall closet.
BUT, and this is a HUGE but for me - I'm extremely sensitive to mold (I had once gotten extremely ill from toxic mold). And ERVs have a reputation for developing mold in their core. Most people probably wouldn't notice it, but I'm not willing to take a chance with that. We put a lot of effort into designing and building our home to reduce potential mold issues.
I also have to take extreme protections regarding mold with my mini split and stand-alone dehumidifier. My house heating load is only 16,000 BTU, and our house is small enough (with our budget also being small), that we don't seem to have a lot of other HVAC options in our moderate, humid climate. But I still keep my eyes open.
On the mold issue, I see that the Panasonic ERVs have an anti-microbial core treatment, but you can also use an inline filter box with MERV13, or HEPA filtration. I am using one of these after the unit (on the warm side) with 14x14x4 filters, so fresh air is filtered again after the core. Hvacquick.com has some decent inline filter boxes for under $200 which you can use with your existing intake fan, or with an ERV.
You can 100% control your ERV (or fans) via a commercial wall mounted C02 sensor from Honeywell (around $250-300), but I've used other makes as well. You'll want one with a relay which in turn will connect to your ERV on/off contacts. I've used this one with success : https://www.co2meter.com/collections/fixed-wall-mount/products/tongdy-co2-indicator-controller-with-relay-for-greenhouses
I used this unit to run a larger Venmar commercial HRV in our net zeroish commercial building project.
That Tongy unit can be set to trigger on at 700 and off at 900 PPM (or higher) and has indicator lights from 600 to 1600 PPM so you can see where you're at. It has a manual override as well.
On the fans, I've sorted the combination of the AC-Infinity or Terrabloom fans combined with a Leviton 0-10V dimmer to control them. The system I'm working on right now (personal) varies fan intake/exhaust fans speeds on an HRV in response to C02, kitchen exhaust etc. but requires a Hubitat (or similar) automation hub so no human intervention is required. This is the link, if you want to explore that option: https://community.hubitat.com/t/success-0-10-volt-control-of-ac-infinity-or-any-ec-fan-motor-using-leviton-zs057-d0z-zigbee-dimmer/104450
If you want to just do this manually, you can use the AC infinity fans (they come with a speed controller, are quiet, and extremely efficient) and a standalone CO2 sensor. A six inch fan from them is good to 352 CFM (way more than you need) but at 90 will be very quiet. This option just lets you tune up the fans based on the standalone sensor readings, no automation.
I really like automation for this application as most HRVs/ERVs are either not run enough, or more than necessary for a given situation. In our 7A zone, they require extra BTUs to run in the winter, so keeping them off when not needed makes a lot of sense.
Thank you very much, Dennis. I appreciate the information you shared. I'll look into it all.
There's a product that addresses quite a few of your concerns called the CERV2, but I don't think it's an appropriate solution because 1) it's expensive (~$8500) and 2) it would require ducting.
That said, you could read up on their product to see how you could configure your house in a similar manner, although it would probably require some technical stuff that I can't really speak to (I'm imagining some kind of custom scripts running on a computer that controls your existing HVAC system plus an added dehumidifier).
If I had to sum it up, it basically uses a 1/3 ton heat pump as an ERV, and can be connected directly to an existing HVAC system and/or dehumidifier. Then you give it set points for temperature, CO2, VOCs, and humidity, and it will do some combination of the following depending on the time of day, exterior and interior conditions, and occupant activity:
-recirculation to distribute fresh air from unused spaces to occupied ones
-"free" cooling or heating - taking in exterior air if it would move the interior air closer to the set points, e.g. cool air at night if the indoor temp is above set point
-energy recovery
-conditioning with recirculation or ventilation
-turning on and off other connected systems as needed to maintain set points
Andy, thank you for your suggestions. I'll read up about it, and see what might be applicable.
Hi Debra,
Thanks for sharing. Its great to see intentional design especially with HVAC. I enjoy the ingenuity.
Let's talk about hvac design more. HVAC should be the first conversation in a house design, not (usually) the last.
One of my issues with wallmount minisplits, they're great for large open rooms, but are horrible for small bedrooms. Often you seen the one wall mount in a common area amongst multiple small rooms (like bedrooms) and we inefficiently try to force the airmixing into the rooms with open doors. I've seen/read some instances of people using jumper fans room-to-room to try to get better airmixing. Otherwise, you're sleeping with bedroom doors open, which in multi-bedroom dwelling, isn't always ideal for general privacy. And don't get me started on how we should be closing our bedroom doors at night for fire safety (unless you're sprinklered of course).
However, ducts can really suck! I mean I think they're great, but really, they can be really horrible to install well, especially in remodels. On new builds, hvac & Duct design should be hand-in-hand with framing/structural design (which is often never the case). The creation of spaces and the conditioning of said spaces needs to be thought of at the same time. This includes cost/benefit analysis of incorporating extra utility space vs using more expensive joists to be able to run ducts through. Think of the difference in cost/labour of I-joists vs truss joists. A no-duct design can really absolve a lot of these issues which is fun to see. As long as its healthy and comfortable.
thoughts?
Jamie
Jamie, I agree that good integrated HVAC design is critical. In designing ours, we had to make some compromises, due to limited budget and health issues. Also, our heating load was only 16,000 BTU, so most conventional heat pumps are way too big. I actually considered installing jumper fans for the bedrooms, but compromised for now with backup baseboard heaters for the coldest winter nights and ceiling fans for summer.
With both the ventilation flow and mini split blower going straight down the hallway to the bedrooms, we get a decent amount of conditioning at the far end of our house.
The risk of fire in our house is pretty small. All of our 15-20 amp circuits are AFCI protected, and there are no combustion appliances.
I think I want to try adjusting our ventilation rates to see if that can help a little to reduce our humidity issues and save some energy. In general, we're pretty happy with our setup.