What about ducting “make-up” and direct exhaust air through an HRV core/box?
It is clear that an HRV is not for providing “make-up” air, but do any suppliers sell the HRV unit with/out motors so that spot specific venting that I’m planing to direct-vent to the outdoors can be ran through an HRV box with the make-up air coming in to temper that cold air?
We are a blended family with seven girls! We have three shower stalls available that I’m completely sealing as though though they are steam showers to help isolate and manage the moisture laden air and exhaust it to the outside. The house is tight, r-50 walls and r-70 roof, triple pane windows, located at 5,000′ elevation in Central Idaho. My plan is to direct vent the showers to the outside and provide make-up air, as needed. I plan to run a RecoupAerator 200dx at night, exhausting the rooms and make-up air coming into the main areas of the house via the conditioned attic and chimney chase, which allows the air to flow down from the open stair cases into all main living areas of the house. (I know opposite from most ventilation which takes air from main areas and puts the air into the bedrooms, but I’m thinking that kids can stink and venting from their rooms will also draw the warm air of the main house into the rooms, reducing or eliminating any need for additional heating in the rooms).
Thoughts? Is there an HRV core available that I can run this exhaust and make-up air through?
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Replies
Eric,
First of all, the UltimateAir RecoupAerator 200 DX is an ERV, not an HRV. If you want to get rid of the moisture in your house, what you want is an HRV, not an ERV.
Explain again: Why do you want an HRV without motors? The motors are useful, so you'll have to come up with a good reason to convince me why you want an appliance without motors.
If you want to install an HRV, it makes sense for the HRV to pull exhaust air from bathrooms or shower rooms. The supply air would normally be ducted to other rooms -- usually, the living room and bedrooms.
If you want to send the fresh outdoor air to your conditioned attic instead of your bedrooms and living room, you can, although your reasoning is unclear. I have no idea what you mean when you suggest that you would like to deliver fresh outdoor air to your "chimney chase."
Panasonic makes small ERVs suitable for single room applications, but they would be susceptible to frost damage from the condensate half the year in your location:
http://www.kitchensource.com/pdf/fv-04ve1-install.pdf
In ID the outdoor air is pretty dry year-round, and there is no advantage to an ERV. ERVs make some sense in hot humid climates, to enable higher ventilation rates while limiting the additional latent cooling loads. Either would dry the house out in ID. It would take slightly higher ventilation rates to do that with an ERV, but not 2x.
With a 6-pack + 1 of girls and three showers you'd probably see fast payback on a drainwater heat recovery no matter how you're heating hot water. The more effective versions are gravity-film types, which needs a vertical section of drain downstream of the shower(s):
https://www.greenbuildingadvisor.com/green-basics/drain-water-heat-recovery
There is at least one vendor of a horizontal version suitable for crawlspaces, but even those work significantly better the steeper you can tilt them:
https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/drainwater-heat-recovery-comes-age
Yes, the UltimateAir RecoupAerator 200 DX is an ERV... I've been told (but maybe this is incorrect) that HRV/ERV's shouldn't be used for venting showers, but that the shower should have it's own direct vent to the outside fan. If this isn't the case, then that changes my approach. Can an HRV quickly remove steam from the three showers? Since I wasn't planing on this approach and was planing on needing "make-up air," then I was believing that the air would be unnecessarily dry and hence the ERV to not further dry-out the winter air for the remaining ventilation. The HRV without motors idea was to have higher spot specific CFM flow at specific places, and not generalized to all showers if only one were being used. I would like to quickly ventilate these places with higher CFM at the specific place, but still have the benefit of the incoming air going through an HRV. Without the incoming air going through an HRV, then it would be cold...so I was going to have that cold incoming air go into a chimney chase where it would be warmed and the warmed air would come out of the chimney chase near the ceiling as the chimney continues through the roof.
Yes, the showers will be tied into a drainwater heat recovery system, Thanks Dana for checking on that.
Is there a better way from what I'm thinking?
Eric,
Some designers choose to exhaust air from their bathrooms with a conventional bathroom exhaust fan; others use an HRV. Before you install a bathroom exhaust fan in a shower stall, check with the fan manufacturer to make sure that shower stall installation is permitted. The fan will probably have to be on a GFCI circuit.
As far as I know, HRV manufacturers allow exhaust air to be pulled from a shower stall, if that's where you want to pull the exhaust air from. But I would check with the HRV manufacturer to make sure.
For a thorough discussion of the pluses and minuses of these two approaches -- bath exhaust fans vs. HRVs -- see this article: Does a Home with an HRV Also Need Bath Fans?
in my mind and if I'm communicating it clearly, then my solution provides the best answer to that debate. Has no one else considered this or done it before?
Using a chimney chase as a makeup air duct seems like an inherently bad idea on a number of levels. Air sealing the chase top & bottom to limit stack effect infiltration drives from pulling in excess dry air 24/7 all winter long is probably the better way to go.
Exhuast fans under dehumidstat control or timers can work just fine. It may seem like you have the whole soccer team showering there every day, but it's nowhere near the humidity load of an indoor hot tub. If you have 9-10 people taking 10 minute showers daily that's still only 1.5 hours out of 24 of high humidity load, only ~6% of the time. It doesn't take monster sized ventilation volumes to manage that.
Yes, the chase would be sealed, no stack effect...more of a closet for chimney pipe that the air make up would go into and then leave after being in the "warm closet" to limit cold drafts with the make up air coming in.
but that wasn't the question...the question is; is there an affordable stand alone HRV without motors that I can duct location specific fans to?
The discussion that Martin referred me to had this debate...pros and cons for both, but this idea seams like it is the best of both worlds...a no brainer that takes the best of both of those worlds and joins them together.
https://foursevenfive.com/introducing-the-lunos-ego/
This will provide up to 12cfm in HRV mode. May not sound like a lot and the mirror may fog up, but it will efficiently exhaust the humidity with heat recovery.
All of the HRV/ERV designs I have looked at, which has been a lot recently, has exhaust coming from the bathrooms and kitchen area (not above the stove) and supply going to the sleeping/living areas. You may want to talk to a few other HRV manufacturers and get their perspective.
I am sure I have seen at least one manufacturer that sells a box with an HRV core in it connected to duct fittings, but with no internal fans, so you can use external fans. I can't remember which one at the moment. I suspect you want that so you can use separate fans in each bathroom and run them through the same core? A more conventional approach is to simple boost the HRV fan speed during and immediately after showers. That means you are exhausting air from other bathrooms when there is only a shower going on in one. But it still works fine.
As an engineer, I tend to enjoy ideas for over-complicated systems that have theoretical advantages, up until I get the bill for them. So I appreciate that individual fans might allow you to concentrate the ventilation where it is needed better. But to do that right, you'd need a fan on the supply side too, to make sure the make-up air came through the HRV, not through various air leaks. And you'd need to control the speed of that fan according to the number of exhaust fans that were operating. So by the time you are done with that, you might was well just use a conventional HRV and run exhaust from all the showers whenever any one is running. And at that point you don't need two HRV systems anymore. You just need one, with a higher speed mode for during the showers.
Once you have an HRV, that takes care of tempering incoming air, so you don't need to do funky things which chimney chases.
As far as directly exhausting shower stalls, I again understand the appeal but I don't recommend it. Instead, you can simply make the shower stall fully enclosed. During a shower, the humidity in the stall will get to 100%. At the end, when the door opens, you will release those 100 cubic feet of humid air into the bathroom at large, but that humidity impact is much less than an ongoing flow of 90% humidity air into the bathroom during the shower. Also, the fully enclosed stall will be warmer, leading to comfort at a lower water temperature, and the high humidity will reduce evaporative cooling as well, again leading to comfort at a lower water temperature. Forced ventilation of the stall during the shower undercuts these advantages. You have to be sure to leave the door open after the shower for it to dry inside, but that happens relatively rapidly because the bathroom at large still has dry air in it.
I second Charlie's suggestion that you just use the HRV boost to get rid of the shower moisture. I find that ten minutes after a shower is plenty. Our shower is open to the rest of the bathroom, which is about 6' x14'. The whole floor is tiled, with Ditra heat under it. Putting in a surround will perhaps keep it warmer during a shower, but it is nice to skip the curb and need to clean the glass surround.
The boost is also nice when you smoke up the kitchen.
Thank you Charlie, that was the kind of answer I was looking for. I was hoping that the make-up air would passively come through the HRV and match the outgoing draw...but probably not?
will I still want make-up air for the Dryer and stove exhaust? it's not a huge stove exhaust...i think mabye 200 cfm but the dryer is probably closer to 350cfm? That's quite a bit at once and the house is tightly sealed with closed cell foam then dense pack cellulose after that in the walls.
Eric: Have you considered a heat pump dryer? Doesn't have a vent so no need for makeup air.
There is a Honeywell made product that has a switch that works on negative pressure. When the house depressurizes from one of the fans, whether it be the dryer (that is reliable and reasonably priced) or the kitchen exhaust or a fart fan, the change in pressure is senses and a damper opens up to the return which has a duct that goes to outside. Depending on the make up air need, there are differing sizes. Six inch, eight inch, ten inch etc. maybe an HVAC expert here can give you the help you need or straighten me out on the matter. Anyone?
Joe,
Do you have a link to more information on this Honeywell control? I'm not aware of it.
I am aware of a different control -- the Exhausto EBC 14, a control that costs $1,500. I have mentioned the Exhausto EBC 14 several times on GBA. The last time the topic came up, this is what I wrote:
The control you seek is called the Exhausto EBC 14. Here is a relevant link:
EBC 14 Pressure Control
I wrote an article about the device for the January 2008 issue of Energy Design Update. In that article, I wrote, "The EBC 14 consists of three components: a control box, an indoor pressure sensor, and an outdoor pressure sensor. The control box includes an LCD display showing the indoor room pressure. The control compares the indoor air pressure to the outdoor air pressure; if the indoor space becomes depressurized, the control energizes a variable-speed supply fan. The control modulates the fan speed in order to supply just enough fresh air to the house to correct the depressurization. (The EBC 14 can control a single-phase fan directly, or a three-phase fan indirectly, by means of a variable frequency drive.)
"The outdoor sensor is sold separately. It must be installed on a roof or exterior wall, and connected to the indoor control with a 50-foot length of silicone tubing. The installation instructions advise, ‘Select a mounting location as free as possible from rooftop obstructions. … Install the probe on an existing structure, like a pole, radio or TV antenna mast. Alternately, the L-shaped bracket can be attached directly to any wall or rooftop. … Obstructions such as trees, chimneys, signs, and buildings all cause turbulence, which results in abnormal and thus inaccurate static pressure. Position the probe as far from the sources of turbulence as possible.’
"The main disadvantage of the EBC is its high price; it lists for $1,500, although contractors will pay significantly less. Moreover, a complete makeup air system will require several other components in addition to the EBC 14 control: the outdoor sensor, a supply air fan, and, in some cases, a heating coil to condition the makeup air."
I have thought about ways to have more flow from the calling bathroom than other bathrooms when using an ERV/HRV as the bathroom exhaust. I concluded that every "solution" I came up with was worse than the problem. One idea I thought about was having a fan for the used bathroom in series with the ERV fan. That would have required some one-way valves to ensure that the bathroom fan wasn't just pushing air into the other bathrooms. In the end, I sized the ERV to provide 50 cfm simultaneously from each bathroom with a shower, plus 25 cfm for the half bath and laundry room. That is much more than I need for whole house continuous ventilation, so I will run it part-time. Drawing from the unused bathrooms in addition to the used bathroom has the advantage of lowering the humidity of the outgoing air to avoid ERV frost problems in winter.
In terms of which rooms to exhaust for odor control, I think bathrooms are better than bedrooms. It is better to control odors via source control than via ventilation whenever feasible. I know of no feasible way to apply source control to the odors generated in the bathroom. Source control for the kids bedrooms would have health benefits beyond odor elimination and is more likely to happen if you notice the odor.
I have also thought about how the range hood and laundry should relate to the ERV. While it would be nice to recover some of the heat and humidity in winter, I don't know how to deal with the lint and grease that may be in these outgoing airstreams, so I rule out sending them through the ERV. I have thought about having them share a hole in the wall to minimize the number of holes. The issue I see there is preventing backflow.
Reid,
In bathrooms without out moisture sources, I've had a lot of success in controlling odors by situating the fan on the wall behind the toilet at the tank level. Of course this comes with all the attendant problems of mounting and ducting it in a wall.
Malcolm, I think we are in agreement. Perhaps I worded my response poorly if you read it otherwise. I was advocating for using ventilation for bathroom odor control and using source control for kids bedroom odor control.
Reid,
Your point is well taken. I was just noting that when you try and deal with odours in a bathroom, it makes a huge difference where the fan is. Locating it directly above the toilet is probably the worse situation. Low down and behind seems to keep things better contained.