Energy recovery ventilaters

triggerhappy24

So I know this is a little out side the boiler spectrum, I just have anyone to ask so hopefully some one can help.

I'll try and make a long story as short as I can. We bought a house last year and the house is 95% efficient as a build....HERS rating I believe? Supposedly it is buttoned up very tightly and insulated very well also. Now there are a few problems I thought where odd when I moved in. 1. The ac unit is 1 ton less then required for square footage of the house. 2. I have 2 bathroom fans that run 24/7 to circulate air. 3. My furnace has a fresh air intake on it.

Now this was all to meet some kinda of code out there. So the problem we had was too much humidity in the summer (over 70% inside house) and could not get any humidity in winter even with a humidifier on the furnace running all the time. In the summer what was happening is the duct work was sweating so bad it was raining in some of the homes (luckily not mine) so the engineer for all this said they want to put in a energy recovery ventilation system to help with the problem.

Now I have one at my work that is the size of a bus but it doesnt really do that good of a job from what I can tell. It will take 80 degrees and drop it to about 75 or 20 degrees and bring it up to about 25. But I really dont know how well it will extract humidity?

Does anyone have any good info or help with it for me? Any info will be greatly appreciated!!

Jamie Hall

First off, there are two flavours of heat recovery ventilators -- sensible heat only and latent heat. The former is just basically a heat exchanger and can be static or dynamic; the latter has to be dynamic, as it attempts by various means to recover the latent heat of the water vapour in the air -- which you really don't want.

Raising the humidity in the winter time is not something they do well. You are bringing in outside air with a very low dewpoint, and although you are warming it, you aren't raising the dewpoint -- which means the relative humidity (which is what you feel) is dropped even further. You will need to have a whole house humidifier to get around that.

Dropping the humidity in the summer time can also be difficult, but it depends on the outside air dew point. If it is low enough -- say in the southwest or plains states -- simply bringing in outside air through the HRV will work -- if you bring in enough of it. Anywhere else and it's likely that you will need a dehumidifier as well.

In any case, on such a tight house I would strongly recommend an HRV. It won't hurt your energy efficiency all that much, but it surely will help your indoor air quality -- which is probably pretty bad, even without worrying about the humidity.

EBEBRATT-Ed

What @Jamie Hall said

triggerhappy24

I'm definitely not going to reject there hrv, but I just dont see it as much of a benefit as say adding a dehumidifier. I live in illinois so our summer can get really humid some times. On the few 90+ days we had this year the humidity out side was around 60%+ and my house was up to 80 to 85. (No joke, thought we lived in the rain forest) That is when I bought a second dehumidifier portable unit for the upstairs. It helped but didnt shut off for about 3 days . Right now our humidity out side has been around 20% but yet the house is still holding 70%. I know those little units are not the best for big areas but it had a 3600 square foot coverage, after about 12 hrs of run I did notice a difference, it just didnt solve the problem as a whole house one may have. Basically I just want to make sure this hrv will fix the problem so I dont have to re-visit this later on. Meaning getting stuck paying for a whole home dehumidifier my self.

I definitely dont see it hurting my air quality, just dont see it resolving the humidity problem in the house that much. The engineer thinks it will but he is the same guy that wrote the code that is not working now. So I have my doubts. Thanks for the input @Jamie Hall .....oh, and I'm not sure what kind of unit it is, all they told me was a hrv.

John Ruhnke

@triggerhappy24

You said "My furnace has a fresh air intake on it." This can be a huge source of energy lost. the teacher who teaches Combustion Analysis pointed out in one of his classes that the codes overbuilt the size calculator for fresh air needed. According to the teacher it is way oversized. I was in a boiler room where I discovered it was freezing cold. I would never recommend cutting back on the size of this because of liability purposes. I noticed how huge the fresh air vent coming in from outside was. In order to reduce fuel consumption we plugged it up and had a grate installed into the door of the boiler room instead. With the combined air of the boiler room and the basement, the boiler was able to meet the fresh air requirements and meet code regulations. This saved some money in fuel.

triggerhappy24

I did! But now they are talking about plugging it up. Which is confusing me because I thought that is how the Hrv's run...? The fresh air vent is only a 3" duct also. So it is minimal, but they are thinking that is what is bringing in too much humidity in the summer with the bathroom fan's running 24/7 .....which they will also be turning off lol

John Ruhnke

There is two types of fresh air inlet. One is for the burner and needs to add fresh air either directly to the burner or indirectly to the boiler room. Another type of fresh air is used by the hrv in tight houses to get rid of the stale air and provide proper ventilation. That fresh air feeds the hrv. They are both needed. They are different.

triggerhappy24

@John Ruhnke I'm sorry if it sounds like I dont understand because I do and dont. I'm just trying to figure out what they may be thinking and what may be the best solution for my house.

triggerhappy24

@John Ruhnke ok, ok, now I see what your talking about. Honestly was not thing about the furnace fresh air for the burner. They are mainly talking about the make up air that goes into the return vent before my filter. I could have described that better. Now I understand what you are talking about. So do you think them adding that will help the humidity then?

John Ruhnke

It depends on how tight the house is. If the house is tight then bringing in fresh air to the ventilation system is a good idea. If the humidity is high outside then that fresh air vent might increase humidity inside. You can always install a dehumidifier in the system to correct this.

triggerhappy24

That's what I want them to do, they want to TRY this first. I honestly think a dehumidifier would be better my self.

Zman

Do you have pictures? Combustion air, for the burner, is very different than the fresh air an HRV would bring in. 3" piped directly to the furnace is fairly typical. A 3" opening to the outside is likely undersized.

triggerhappy24

@Zman I dont have pic of the hrv. They do not plan to install it until the end of this month. But I can take some of the fresh air coming into the house if you like.

triggerhappy24

I am so sorry I just realized I have been typing HRV when it is suppose to be a ENERGY RECOVERY VENTILATOR. I must have typed it and my auto correct changed it on me and I have been going with it this whole time. So to try and correct this they want to put in an ERV not a HRV. It doesnt look like there is that much of a difference between the 2 I just want to make sure I call it what it is

HVACNUT

If your home is under 3 air changes per hour, it's pretty tight. The 24/7 bath fans help achieve those air changes. You stated the air conditioning system is 1 ton smaller based on square footage. Is it possible the specs on heat and A/C were changed because the rating on the house changed? Does the home have open or closed cell foam insulation throughout? Maybe the original plans called for batt insulation at a lower R value, then changed to foam with a much higher R value, therefore making a revision to the size of the A/C system to match the new heat gain calculation using a manual J.
Since there's already a 3" hole into the return duct to outside, rather than an ERV, look into an Aprilaire ventilation control system like its 8126X. A 6" duct from outside to the return duct (before the air filter) with a motorized damper. You adjust the settings using humidity, outdoor air temperature and run times. If your A/C system is rated at say 1200 CFM. With the ventilator pulling in 200 CFM, the system will keep the home at a slight positive pressure to get the air changes. You should be able to cut the times on the bath fans as well.
This whole topic could be moot if the A/C system isn't functioning properly. 80% RH is not good. A whole house dehumidifier can be incorporated into the HVAC ducts. A quality steam humidifier shouldn't have a problem making 30-40% RH in the winter.

triggerhappy24

@hvacnut what the air change rate in the house is I really dont know, i do know it is low which is why the had the fans. Yes. I talked to our HVAC guy at work about this also and he said the same thing about the unit being smaller. So that very well could be. This year I had a company come out to look at the unit (not the same ones that installed it) to have it looked over. Mind you I checked my refrigerant charge my self and found I was about 8lbs short on charge according to the pt chart. He found the same issue and added. It helped but still didn't help the humidity in the house. But the unit ran about a half hour less then it used to after a recharge (no, he did not find a leake. Just under charged from the start) the control system that you talk about was installed on a house that started the whole thing off. It help to a point but now left the house with stale humid air. And that is how we are at where we are now. The builder had the H.E.R.S rating people come out and test the house before and after and that is what they said they found.

This whole thing is crazy for a new build home. Regulation where made without even a trial period. They also made them in one area of the country without thinking about how it will work in a different climate of the country, at least that's how I feel....is it true, could be?

Yes the 80% in the house when it is 85 degree outside and only 20 to 30% humidity is not good. The small dehumidifier are "HELPING" but not a permanent fix I want. I feel like they are trying this ERV to fix the stale air more than the humidity issue in the house. It feels like the way this is all going, I'm going to have more equipment in my home for hvac then at work!,

Jamie Hall

The ERV (or HRV, take your pick) will indeed help with the stale air in your house. Guidelines on air changes vary, but 2 to 4 complete air changes per hour is not a bad place to start.

However.

They won't, and aren't intended to, help with the humidity problems. For those you will need both dehumidification (in the summer) and humidification (in the winter). Both can be added to your existing HVAC system.

And yes, regulations which make some sense in one part of the country may not make any sense at all in other parts. Not going further on that one.

triggerhappy24

@Jamie Hall that is exactly what I thought it would do. I had the builder come to the house today to look at the fixes they have done. They said they are not looking to add a dehumidifier in the house. But more to fix the air rate exchange per the code. So I guess I will be buying a whole house dehumidifier next summer and installing it into the furnace. Thanks for the help guys

ratio

If your system was 7 lbs low, I can't see how it was working at all before. With a small system and a short lineset, that could easily be 50-80% of the charge!

What kind of runtimes are you getting with the current system? When it got up to 80-85°, was the system running all the time? Any way to measure the condensate produced (time it takes to fill a pint mason jar or something like that)? Has a blower door test been done to see if your house actually is as tight as it's supposed to be?

triggerhappy24

I know when I saw it I was a little shocked myself. Even the company that came out was really shock. Even more so it wasn't to bad in the house but ran just about all day. When it was above 85 it did litterally run for 15hrs at a setting of 73. That is when I ended up checking and then making a service call. Now that it has more freon it has been way better were it will actually cycle mid day now. But still seems to be humid in the house. Nest is saying 60 and so is the humidistat I brought from work. The blower door test was done by the builder when this all started. Didnt see results, but the did come back to fix a few problems nothing major. It funny, all these problems on a new build!