HRV/ERV... Why not a pipe?

[EatenByLimestone]

After I finished foaming the basement this spring I noticed that the bathroom fan wasn't evacuating the steam like it should. Opening a window allowed it to evacuate like it should. Luckily I keep windows open all summer long.

So, now I need to start looking at winter. Windows will soon be closed.

My boiler was way oversized and broke down, most likely from short cycling.

The 110k btu boiler is being replaced with a mod con 13-50k btu boiler. That'll draw outside air. No worries there.

But what about regular air exchange?


I've been looking at hrv and erv systems. Why do they need to be powered? Why not install a pvc pipe out the wall and let it exchange air when negative pressure develops due to fans, wood stoves, doors opening, etc happens? In a tight house, do you really need to worry about heat exchangers on this air? If windows are usually open in the summer, is moisture exchange in the erv really a concern?

What says the brain trust?

 

[STIHLY DAN]

If its 0* outside that is the temp that will be entering your house with a pipe. An ERV will use exhaust air to warm the incoming air. Could be a 40* difference pending on the type and quality of the unit.

 

[byQ]

First you need to figure out which one best suits your climate - an ERV or HRV. These devices in the USA basically work on the principal of an interface between cold air and warm air so that the cold air is warmed and the warm air cooled, thus an exchange. So like said, your entering air is less of an energy taker.

Interestingly, in Europe they have 'HRV's' that use water coils that are underground. This greatly increases the efficiency - so you are getting exchange air that is closer to the inside air.

 

[blades]

just a tube- in olden days what would be done is snake that tube back and forth across basement ceiling or up and down the walls to allow for some temperance of the incoming air. Additionally there could be a box with a filter in the incoming air flow. no fans but this terminated to the cold air return of the conventional hot air furnace. Never saw anything that addressed hydronic systems ( or I didn't pay attention to that portion back then) and before someone jumps and says it doesn't work - pasture droppings to you, as it does. Just got to use a very long run of tubing. I had over 100 ft along the sill area of the basement walls. Current home has a hrv in it, does about as much as the old tube did- except the old tube was 100's less, and didn't require electric power ( just had to replace one of fan motors on that rig, $ ouch, original mfg long gone). so not every modern thing is any better than old school. current hrv is always changing air ( i will have to look at that portion - a relay hooked to the furnace blower motor terminals to start stop the hrv seems like a good idea) old tube only when air was being pulled by furnace fan.

 

[begreen]

An ERV preheats the incoming air. If you have the right topography you might be able to deep bury an air intake pipe or two to take advantage of natural earth tempering of the intake air. This would preheat the incoming air to earth temp and could also be used for some summer cooling air. This was done by a long ago hearth.com member with claimed reasonable success. I think it was also suggested in an early Mother Earth News.

 

[woodgeek]

It is unlikely that your house is tight enough to need forced mechanical ventilation OR some form of makeup air. It may be that your bathroom is that tight....but you could shave the bottom off the door. Done.

Get somebody to do a blower door test for cheap or free. It will confirm.

In the borderline leaky/tight case you might want some mechanical ventilation during shoulder seasons. For this, you can get a timer that cycles one of your bath fans for a few minutes per hour, and turn that on and off seasonally. Done.

 

[maple1]

We have an HRV, it is usually shut off all winter. I have a basement window right behind the boiler I leave cracked open for combustion air for the boiler (with FG batt stuffed into the crack), and stack effect (don't think we have a lot - fairly well sealed) seems to take care of the rest. Even with the heat exchanging of the HRV, if it is running when it is 0° out, and it is 70° inside, that means it is putting 35° air into your living space (simple math like) and it creates a noticeable chilling effect. So can't imagine wanting to bring in 0° air directly to the living space.

Windows are open pretty well all summer, so it doesn't get used then either - usually only intermittently in spring & fall if humidity gets creeping up or we find it 'stuffy'.

 

[EatenByLimestone]

Very possible that the bathroom is much tighter than the house. I only noticed the issue after I finished foaming the basement though.

I was talking things over with an ex co-worker and he had access to the blower setup at his company. If he can borrow it, I'll run one.

 

[velvetfoot]

This bathroom isn't in the basement, right?

I'd check the fan flapper too. Mine gets stuck when it gets cold out, and I stick my head out the window and poke it open with a stick. It's an under eave arrangement. There might be an additional flapper at the fan itself.

 

[DickRussell]

.... Even with the heat exchanging of the HRV, if it is running when it is 0° out, and it is 70° inside, that means it is putting 35° air into your living space (simple math like) and it creates a noticeable chilling effect......

The efficiency of a heat exchanger depends on its configuration. A simple countercurrent flow exchanger of sufficiently large area for heat transfer could warm up the incoming air to something very close to the temperature of the interior air, while cooling the outgoing air to near outside temperature, while giving up some heat from condensing moisture along the way. A typical HRV has one or two cross-flow exchanger units, which is much less expensive to build with adequate heat transfer area and which provides more area per unit volume. However, the efficiency of cross-flow typically is less than that of pure countercurrent flow. Still, having two cross-flow cores in series starts to approach the efficiency of countercurrent flow. My Lifebreath 195ECM HRV has two cores, and the mfg literature says heat transfer efficiency is 88%. It runs 24/7, dumping tempered air into the ducts of the heating system while drawing "stale" (hardly that) from the bathrooms and a corner of the kitchen. I don't really feel any cold drafts from the registers when the heating system is not running.

 

[EatenByLimestone]

This bathroom isn't in the basement, right?

I'd check the fan flapper too. Mine gets stuck when it gets cold out, and I stick my head out the window and poke it open with a stick. It's an under eave arrangement. There might be an additional flapper at the fan itself.

First floor bath. And when I ran the hose I was careful to pitch it so it would drain water that condensed inside.


I checked the flappers when I noticed the issue. All good.

I should have word on the blower door next week.

 

[semipro]

What a great problem to have! I wish my house was so tight.
If opening a window allows the bath to vent then the problem must be a lack of make-up air. If the window you're opening is in the bathroom then Woodgeek has it right. If the window you're opening is outside the bath then you need to look at an outside air source. The choice then is basically creating a leak; i.e. the pipe you propose or installing an HRV or ERV.
I really do envy your problem though. I'm spending a lot of time and money doing a deep energy retrofit just so I can get to where you are.
Good luck!

 

[georgepds]

An ERV preheats the incoming air. If you have the right topography you might be able to deep bury an air intake pipe or two to take advantage of natural earth tempering of the intake air. This would preheat the incoming air to earth temp and could also be used for some summer cooling air. This was done by a long ago hearth.com member with claimed reasonable success. I think it was also suggested in an early Mother Earth News.

Well, burying tubes leads to standing water in the tubes and all the problems that come with it (legionnaires' disease?)


here is a link to a guy who likes what he did

http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/my-earth-tube-story

Here is a comment form the editor of GBA who casts doubt on the technique

The conclusions of the CMHC researchers were as follows:

"This study has shown, through a literature search and interviews with researchers, owners and operators, that EAHXs [earth-to-air heat exchangers, or earth tubes] may have benefits when used under the right conditions and in the right climate, but also that they are very subtle systems which require careful design and operation to be successful. The literature shows that an improperly designed system will not work as expected, or result in poor air quality, etc. leading to disenchantment with the system and in many cases decommissioning: it is often very difficult to fix EAHXs once the trenches are back-filled.

"The literature also shows that controls, air quality, and thermal memory of the ground are but three of the areas to pay close attention to when considering an EAHX. It also demonstrates that an EAHX can be redundant when used in conjunction with heat recovery ventilators (HRV), and that the economics are rarely favourable."

 

[begreen]

Well, burying tubes leads to standing water in the tubes and all the problems that come with it (legionnaires' disease?)


here is a link to a guy who likes what he did

http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/my-earth-tube-story

Here is a comment form the editor of GBA who casts doubt on the technique

The conclusions of the CMHC researchers were as follows:

"This study has shown, through a literature search and interviews with researchers, owners and operators, that EAHXs [earth-to-air heat exchangers, or earth tubes] may have benefits when used under the right conditions and in the right climate, but also that they are very subtle systems which require careful design and operation to be successful. The literature shows that an improperly designed system will not work as expected, or result in poor air quality, etc. leading to disenchantment with the system and in many cases decommissioning: it is often very difficult to fix EAHXs once the trenches are back-filled.

"The literature also shows that controls, air quality, and thermal memory of the ground are but three of the areas to pay close attention to when considering an EAHX. It also demonstrates that an EAHX can be redundant when used in conjunction with heat recovery ventilators (HRV), and that the economics are rarely favourable."

The system needs to be designed correctly. That means that the pipes should be sloped away from the house and self-draining. Sizing, length, critter screening, etc. are all part of the proper design.

 

[georgepds]

The system needs to be designed correctly. That means that the pipes should be sloped away from the house and self-draining. Sizing, length, critter screening, etc. are all part of the proper design.

Here is another GBA post on the matter

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/do-earth-tubes-make-any-sense

Basic comment is proper design means 21 feet deep. In my neck of the woods that would put you underwater.. hard to provide good self drainage in that condition

Then again, you'll have to vent the tube to avoid radon contamination, if you are in a high radon area..

and finally a comment from a guy that loved the idea

"Ultimately, what really sealed the deal is the impracticality of it all. From installation, maintenance, repair issues, contamination, proper sizing (both size and surface area/heat exchange properties), longevity (materials & site) -- it just doesn't logically pan out."

 

[georgepds]

and then there is the observation that they just stop working


"Aside from the problems mentioned by others, back in the late 70s we found in monitoring some experimental projects for ERDA that often the tubes stop working after a short while due to the poor conductivity of the soil adjacent to the tube wall. If your soil is relatively non-thermally conductive (as most non-saturated soils are) the 2" of soil adjacent to the tube wall rapidly approaches the temperature of the air passing through the tube, at which time your tempering effect stops to provide any significant benefit. You can make use of the earth's temperature only to the extent you can conduct heat through it."

Read more: http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/do-earth-tubes-make-any-sense

 

[begreen]

Sounds like trombe walls and other designs of the 70's this has had limited success. Old elky is long gone from this site so no way to follow up on his installation though I'm pretty sure it wasn't buried 21 ft. deep.

 

[EatenByLimestone]

Elky... wow, I remember him! Wasn't he a building inspector or something similar? Has to have been over a decade since he was on.

 

[begreen]

Yep, inspector gadget and local tv star.

 

[woodgeek]

Memories....

 

[begreen]

LOL

 

[lml999]

We have an HRV, it is usually shut off all winter. I have a basement window right behind the boiler I leave cracked open for combustion air for the boiler (with FG batt stuffed into the crack), and stack effect (don't think we have a lot - fairly well sealed) seems to take care of the rest. Even with the heat exchanging of the HRV, if it is running when it is 0° out, and it is 70° inside, that means it is putting 35° air into your living space (simple math like) and it creates a noticeable chilling effect. So can't imagine wanting to bring in 0° air directly to the living space.

That hasn't been my experience...we have a Fantech HRV running year round, and on a cold day in New England the fresh air delivered to the living space measures just a few degrees cooler than the ambient room air.

 

[maple1]

I haven't actually measured the incoming air temp. I should do that some cold day this winter. But I know you can feel it, sitting in the area of the air duct. It's quite uncomfortable. Ours is a 20-25 year old Venmar. Which I think is almost on its last legs - last time I had it running a couple weeks ago, it was cycling off & on before hitting the humidity set point. Already replaced the motor in it once, somewhere between 5 & 10 years ago.

 

[peakbagger]

One of the tricks installers use is to duct the incoming fresh air to the back of the refrigerator. It keeps the unit a bit cooler and most folks arent sitting near it to notice the draft.

 

[blades]

and that worked pretty well until they started putting all the coils underneath instead of the panel up the back.