Air to Air wrecking a radiant system

Kevin_in_Denver_2

The radiant guy must have had a system that couldn't keep up with the fresh air exchange in the bathrooms, since they were seeing up to 100cfm continuous. I guessing now, but the perceived stratification might have been chilly air at ankle level.

You shouldn't have any problems especially if the HRV is on a timer.

ScottH

Air to Air wrecking a radiant heating system

I am working on a project installing an Air to Air exchanger in a house with radiant heating. The radiant heat
installer showed up and was rather upset that I was installing an Air to Air instead of bath fans. He said that the 250 CFM of the Air to Air will cause the radiant system to not work properly. Supposedly the air movemet stratifies the air. Has anybody else had a situation like this. Your input would be greatly appreciated. The house is 4800 sf.

Kevin_in_Denver_2

An HRV wouldn't cause stratification

Air movement of any kind and the introduction of fresh air into the house theoretically helps mix the air and reduce any temperature stratification.

This radiant guy must have had some problem in the past that he still believes was caused by the HRV. Find out about that issue and see if it applies to this job or the homeowner will be really unimpressed with the finger pointing that is starting during installation.

Now, there is a school of thought that says you still need decent bath fans (eg. Broan HRV installation literature)as well as the HRV. The theory is you get the smell and humidity out quickly.

Brad White_24

I agree with Kevin,

air movement will tend to de-stratify (and with radiant, "de-stratify what?" is an obvious question).

If the HRV exhaust is concentrated in the bathrooms and the quantity is sufficient, I cannot see the need for booster exhaust fans. I have a Lifebreath 200 which kicks up to high speed based on humidity if showering is a concern. Even on low speed the mirror never fogs.

Constantin

Ditto...

The Lifebreath TRV that exhausts the three bathrooms in my home does a great job and even after a long shower only the exterior windows are briefly fogged. 5 minutes later, that too disappears.

Extreme climates aside (where warming the incoming air is mandatory, for example), I see no reason why a HRV/ERV cannot do the bathroom exhaust duty for a home. Fewer mechanicals = fewer headaches in my book.

ScottH

The HRV is a lifebreath 300. It is in an extreme temperature area. And it will have an inline duct heater installed to temper the fresh air back to the house.

Brad White_9

Does the OA from the HRV

go to the central return duct and get conditioned there? Mixed with the rest of the house? Point being is you seem to have accounted for the heating load imposed at some level.

The concept remains that the HRV should keep the bathrooms dry and assuming a ban on burritos, well...

Should not affect the radiant floor heat in any way I can determine.

Paul Pollets

HRV's

The HRV will not affect radiant performance. It will enhance the indoor air quality and overall comfort of the home.

The HRV should NOT take the place of bath exhaust fans. The unit cannot remove large amounts of air required when the bathroom is "working" and leave high humidity and odors. We always install a quality bath fan (Panasonic, VentAxia or Kanalflacht) and put a return from the HRV ducted into the bath for continuous humidity removal.

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Brad White_9

I would qualify that a bit, Paul

in that it depends on the exhaust rate out of the respective bathroom versus the input of humidity. Mine for example, works wonderfully as the sole exhaust means.

Agreed if spread out too disparately you can lose control and a booster or dedicated fan would be worth it. But properly applied and controlled (humidity, manual timer to high speed), I cannot see an issue. To me it does two things in one and that is a good thing.

Respectfully,

Brad

Paul Pollets

CFM

35cfm removes humidity, but will not remove odors quickly like a 110CFM fan or larger. I've seen many HRVs installed with a return into the bathroom only and no exhaust fan. The owner complains of too much humidity and odors. We were advised by LifeBreath reps many years ago that while a return works...a supplemental exhaust fan works better.

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Constantin

Good Point, Paul!

That is why I tried my best to get 100+CFM of flow out of each bathroom when the occupancy sensor detects movement (20min delay) by kicking the TRV into high gear, followed by the lowest speed setting the rest of the time. Seems to work, even when it's very cold outside.

The TRV pulls out of the bathroom and returns into the main AC return. Each bathroom has a AC supply and there are returns sprinkled throughout the rest of the house. So far, this system is working well for me and I look forward to inspecting the units in a month.

ScottH

Design paramaters of the system were 150 cfm from the master bath area and 50 cfm each from the laundy and two smaller bathrooms. It is a dedicated system (there is no forced air system). Hence the inline duct heater.

Brad White_24

But, Paul

of course 35 cfm is not enough. No wonder it does not work the way you describe. Why 35 cfm? Arbitrary and obviously not enough. Any system will not work well if you do not apply it correctly was my point.

And to supply the air to the bathroom and not exhaust it, of course you will have an odor and humidity problem. Bathrooms are kept under negative pressure, not positive.

My system exhausts 110 cfm on low speed and a mechanical twist timer boosts it to 140 or so for the duration. The supply-side serves the laundry room and bedroom closets as a means of freshening things and to keep dust out. When the dryer starts it goes to high speed as make-up air too. But only the bathroom and to a lesser extent, the laundry, is exhausted.

This illustrates my point that properly applied (not spread too thin) it can and does work well for bathroom exhaust.

Also, 35 cfm does not meet code in these parts.

Best Regards,

Brad

Unknown

ASHRAE specifies 20 cfm continuous ventilation for bathrooms, or 50 cfm intermittant.

As usual though, it depends on establishing expectations with the client. continuous lower flow w/boost rates of around 50 cfm can be fine for bathrooms, if you establish the limitations up front.

What's the point of doing an HRV, and then taking the most frequent air exhaust demand and just blowing it outside without heat exchange? If you have to, get a larger HRV, and run it at lower speed settings for regular duty. You can probably afford the upsize for the cost of a few bathroom fans.

Paul Pollets

Lifebreath

Yes, it can work, but I prefer larger exhaust capacity for at least 10-15 min. after a shower, bath or using the WC with odiferous results. NRT Bob is quoting ASHRAE minimums. Again, I find these too small for most modern bathrooms and particularly the master luxury baths that are often larger than 100SF. We like to design our HRV systems for at least 30-35CFM per outlet. We will size the HRV accordingly with either min. code requirements or larger, if the owner wants more air exchange.

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Unknown

you are sizing for 30-35 cfm continuous?

I think if sizing for a 50cfm on boost, that's often a range my ports are falling into as well. I was quoting the minimums to clarify the range the previous poster was asking about, not because I like such a low flow myself.

But overall you do have to watch out as well... you don't want to overventilate! I do think .35 ACH continuous is a hard maximum, with intermittant boost rates that are higher.

Ich Wundermich

HRV and WC

Have you considered POSH grills in your WCs?

Paul Pollets

Design

sometimes the WA state air change codes can be met at 25CFM. We're required to provide .35ACH to each habitable room in new construction. Some designs, like home theaters (very popular out here) use .5 to .1 ACH. The great thing about these systems is they can be modulating from min to max air exchange, programmed for individual or whole house setbacks and set up to be a key component of the "Healthy Home". Every home we've done with an HRV has superior comfort and indoor air quality to the homes just on bath fan timers and a whole house attic fan.

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Unknown

You are supposed to provide .35 ACH, or the room must have .35 ACH including natural ventilation? Not that you can easily measure that until the house is built

Paul Pollets

ventilation

the make-up air must be provided in each habitable room, when using the prescriptive method. Most install a 4" venturi wall unit which can go in the closets on an outside wall. Doors must be undercut to allow air to be moved to the exhaust fans....

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Paul Pollets

ACH vs CFM

Brad, the 35 cfm was for HRV design, not bath exhaust requirements.

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kevin coppinger_4

I can see...

an hrv messing up things if it is run on a continual basis. a timer is needed....kpc

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[Deleted User]

35 CFM...

at design conditions in Denver moves around 3,000 btuH. Thats a LOT in a geo based system. I like the idea of a motion detector, for fans and lights. So what, every once in a while you have to shake your arms around to finish the article... No big deal:-)

Thats a LOT of btus from a small space. I thik our local requirement is .35 cfm per square foot, with a minimum of 75 cfm on bath exhausts...

That's 6,000 btuH which is even HARDER to swallow in a small area.

Whatsa mutha to do?

Infiltration will KILL ya, I'm tellin' ya. And missed mechanical exfiltration is GUARANTEED to break the BTU bank on radiant flooors. You can only get those floors so hot before they start negatively affecting your well being.

Proceed with caution:-)

ME

Constantin

I agree...

I put inexpensive Leviton occupancy sensors into my bathrooms and they work great. Originally conceived for lighting needs, these detectors incorporate the possibility of a dry contact (which the Lifebreath wants), adjustable time delays, and adjustable active sectors for detection purposes.

With up to 3 detectors per "PowerPack", you can easily tie three bathrooms into one 300+CFM HRV... Plus, the control wiring is all low-voltage, allowing you to bypass a need for a electricians license to install everything but the powerpack (my HVAC contractor and electrician loved that because that was one less thing they had to coordinate).

I also agree that minimizing/controlling infiltration is a desireable goal. I'd prefer to keep homes pressure-neutral rather than exhausting with abandon from one room while not paying attention to the possibly negative consequences elsewhere (i.e. pulling make-up air down a chimney flue, for example).

Paul Pollets

Somethings being missed...

Kevin, we run our HRV's 24/7. Many have timers or programmable fan controls that boost or lower the fan speeds according to program. If a Lifebreath 200MAX is installed it can provide 200CFM at high speed. If 10 rooms were ducted with the unit, each room would get appx. 20CFM with a small amount lost due to duct frictions. 20CFM can barely be felt at the outlet. The unit can reclaim about 70% of the heat passing thru the HX. How is the unit going to rob BTU's from a radiant system??? I've installed over 100 of these units in homes from 2000SF to 20,000SF. Never had a problem. Never.

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Unknown

I am not sure I asked the question clearly (or I don't understand your answer).

ASHRAE specifies ..35 ACH for living space (or the room by room specified rate method), however it also notes that in most buildings this is provided with "natural infiltration". Thus it is reasonable (I believe) that when doing ventilation for IAQ, you are looking to provide the difference between .35 ACH and the natural infiltration expected in the home. There are other factors as well of course.

So I'm wondering if you are required by code, or by personal preference, to provide .35 ACH via the mechanicals, or whether you take into account natural infiltration as well?