Heat Recovery Ventilator vs Energy Recovery Ventilator (HRV vs ERV)

[johns]

Can anyone explain the differences to me between a Heat Recovery Ventilator and an Energy Recovery Ventilator in terms of how they work and in what types of situations either one works better??

Trying to understand which type would work best for applications of removing excess humidity in this hobby. Also which ones work best under what types of outside weather conditions. (ie. where I live it gets very cold for a few months out of the year, and I've heard an ERV doesn't work as well in that environment, but I want to understand WHY).

I started this thread yesterday, feel free to take a look at the discussion so far:

http://reefcentral.com/forums/showth...13#post8364513

[mhurley]

I have an HRV in my fishroom.

The big difference as I understand it is that an ERV also tries to balance moisture levels as well as temperature...an HRV simply swaps outside and inside air and balances the temperature.

[wmilas]

I just installed a HRV.

Both HRV's and ERV's are used to swap stagnant air inside with fresh air from outside. HRV's internally have a chamber that "mixes" the cold outside air with warm inside air thermally. That sounds kind of confusing but its not. The cold outside air comes in in a series of channels with thin walls and the hot inside air goes out channels with thin walls next to the cold air. The way these channels are setup reflects on the energy exchange percentages.

The idea is to heat the cold outside air so when it enters the house you aren't losing too much energy.

ERV's don';t do this. They simply swap the air. They are set up more for warm weather climates. Adding heat to the incoming air would be net energy loss here.

Both HRV's and ERV's can be set up to control humidity... thats the controllers job and is particular to the brand. Keep in mind its not a "spot" exchanger.. it pulls from the ductwork of the whole house.

I live in Chicago and in the winter it can get brutally cold. I'm in a new house that is insulated well and it gets pretty stuffy in the winter time. The HRV is going to let me exchange air without me opening the window when its 0F outside (which drives my wife nuts).

Basicly I jsut tore out the upstairs and downstaird air conditioners/furnaces that were builders specials and redid the whole thing. I installed large Hepa filters, media filters, air exchangers, high effeciency vented/multiple speed/burn furnaces, and air conditoners along powered humidifiers and outside sensors. The thermostats talk to all of these and monitor ouside air temperature, humidity and control air exchange and humidity inside so as to not fog the windows in the winter and not have the whole house at 60% humidity int eh summer.

Oh, I'm also installing a low prodile gass heater int eh garage for the "work shop"

Think of it as extreme tank filtering, only for the house. Yes its expensive as hell, but its going to be worth it. The upstairs hepa is already running and you cant BELIEVE how fresh it smells up there... its like spring.

[johns]

wmilas-

I am far from an expert but I have been doing a lot of reading the past few days and talked to a few people on the phone. But, I dont believe that ERVs simply swap the air.

I think mhurley is right, that ERVs are meant to allow for ventialtion and in doing so, control for temperature AND HUMIDITY. HRVs dont necessarily transfer humidity directly, but there may be some moisture transfer as a by-product of just the heating or cooling of the air (cool air hold less moisture). Since the problem in our hobby is typically involving temp and humidity, I think they should looked at more carefully

Why ERVs are considered to be for warm weather climates is still beyond me. The one company I talked that builds ERVs is in WI. They are one of a few of companies that is considered to be ahead of the game, and they claim that the vast majortity of their units are sold and successfully used in northern states.

With no direct control over humidity, I have been told that HRVs can tend to over-dry the home in the winter, and in the summer will bring in more humid utside air without the added dehumidification-effect of the ERV.

Check this link someone else provided to me:

http://www.renewaire.com/New%20Web%20Files/ERVvsHRV.pdf

[wmilas]

Take a look at:

http://209.250.87.54/HR150.PDF

and:

http://www.lennox.com/pdfs/brochures...entilators.pdf

I'm installing lennox gear so these two pertain to me. As far as I can tell the lennox units are the same/rebranded honeywell units.

Notice that the HRV's have:

1) Defrosters
2) Humidifier control
3) Remote timers and himidity control

The ERV versions do not have these. The reason is that ERV's are meant to be put into service in the part of the country that has high outside temperature and humidity. Both HRV and ERV's exchange air. If the outside air is more humid than the inside air (it will be in teh south) then its impossible the for the air exhange to lower the humidity in the house. Remember the HRV'sERV's dont have a built in dehumdifier. They swap air to lower the total inside humidty. If this air swap would raise the humity, well then its not beneficial.

As far as I can tell ERV's also have some type on humidty condenser and drip pan that uses the inside air to cool the outside air coming in to dehumidify it.. but not by direct air exchange. I'm not 100% sure on this because I did not research the erv's as the dont relate to my needs.

Also it would make no sense for a erv to have a defrost module. As far as humidty control I believe the consenser on the ERV is not adjustable since you cant regulate how much it condenses. With the HRV if the humidty outside is less than inside you can lower humidity by running the exchanger longer with a net air swap.

I do know that HRV's do vent humid air directly outside.. as I've tested mine and its doing that

[wmilas]

I've dug around and thought a bit more. ITs possible that the ERV's are HRV's without the thin wall heat exchanger.. but instead with the moisture condenser in its place and no defrost control. This would make sense... The lennox literature says that the ERV reduces outside moisture coming into the house for the ERV but does NOT state that for the HRV.

Without having an ERV to tear apart and compare to my HRV im just not sure.

I do know that my installers know exactly what the HRV does but cant clue me into the ERV. They state (jsut called them) that they dont install them in this part of the country and have no practical experience with them.

Which is better for a fishroom? probably depends on where you live. They both will net lower the humidity in the house. Would an ERV do a better job in a fish house in the south. For sure. Would it do a better job in the north? I'm not sure. I know it would be much less effecient and my installers warn me that tthey ahve been told that an erv in the north will frost up and lock up without the hrv defrost module.

Hope this helps.

[mhurley]

If I sidetrack this too much for the original posters needs, feel free to ignore me (I'm used to it).

My HRV is solely decicated to my fish room which happens to be next to an outside wall. So I have the inlet/exhaust puched right out of the house. Then I put the opposing inlet/return punched right into the fish room on opposite sides of that 10x10 room. The HRV circulation never touches the home ductwork system.

So my question is, should it? My original intention was to only vent heat/humidity out of the fishroom. I got the HRV for a steal from a guy who was getting divorced. This is a whole house unit so I am likely wasting its' capacity. Should I have it re-worked to hook into the whole house (I too have a newer fairly tight home)?

[wmilas]

Well What I'm doing is this. The HRV pulls from the ductwork for the air it exhausts. The fishroom has an outlet thats the first "outlet" in teh chain. So while it pulls from teh whole house, it pulls proportionately more from teh fishroom being that its the first vent. The vent is of the type that you can manually open and close so I can vary how much is pulled from the room. Its half open atm.

This was easy to do because the fishroom is in the basement... in the same room as the hot water heater (highly recommend going with a AO Smith Vertex power vent.. its 90+ effecient, has a built in hot water (european style) exchanger with a 50 gal backup tank... its going to pay for itself in the first 2 or 3 years the way my wife and kids go through hot water), downstairs furnace, injector pump ect. So adding the return int he room was cake.

You might consider doing this. You own the unit anyways.. a little bit of plumbing and you can do the fish room and the whole house in one shot.

[namdrib2]

HRVs are typically only used to reclaim sensible heat (heat that you actually feel as a rise or drop in the temperature) from the exhaust air stream that is discharged to the exterior. This is typically done by use a plate type heat exchanger, one made of metal channels. An ERV is used to also reclaim the latent heat (that that you cannot feel). Latent heat is the amount of heat required to change a substance's state (ice to water) at the same temperature and pressure. Latenet heat is what is required for the removal of moisture from the air. This is usually done with a desicant material on a wheel that spins through the exhaust stream into the fresh air stream, which is moving in the opposite direction.

A plate type or HRV would be best suited for a fish room as we are typiclly trying to get rid of moisture from these spaces.

[Double-J]

Is this model considered an ERV? The price on it seems much lower than the other models I've researched but it claims it is an Air Exchange ventilator


http://www.rewci.com/faairexveae.html

[namdrib2]

When it comes right down to it they are all energy recovery ventilators. They both transfer energy from one air stream to another. Heres a link to Fantech's website which explains the actual differences which has more to do with climate that you are in than anything else.

http://www.fantech.net/hrv_erv.htm

[johns]

Still not quite so simple (at least to me - I like to understand everything). Because it depends on who you ask.

Looks at the map on Carrier's site:

http://xpedio.carrier.com/idc/groups...f?SMSESSION=NO

and then look at the product info at Renewaire:

http://www.renewaire.com/New%20Web%20Files/ERVvsHRV.pdf

And here's a pretty easy to understand write-up I just found about how ERVs work, with a neat little cartoon:

http://www.renewaire.com/for_your_ho...es_it_work.php

Also, namdrib2- not all ERVs use a dessicant wheel. There is another type of ERV design using a resin treated 'paper-like' static plate in a crossflow pattern. From my understanding, one of the benefits of this design is they dont frost up or freeze up, and so they dont require a defrost cycle.

I am providing a lot of ERV information, because I keep getting bombarded with "HRV-HRV'HRV" on the boards, whereas in talking to people out in the field, I get a mixture of responses. I actually havent decided between the 2 for certain yet.

[johns]

OK. I'm finally collecting my thoughts here. I'm still waffling back and forth between HRVs and ERVs, but here are few more points.

Both HRV and ERV's exchange air. If the outside air is more humid than the inside air (it will be in teh south) then its impossible the for the air exhange to lower the humidity in the house.

This is true. But if are going to use this type of ventialtion in the summer, an ERV is still the better choice. That way the VERY humid incoming air from outside can at least transfer part of it's humidity to the outgoing air. That is why many poeple who have HRVs wont run them in the summer. You'd be bringing in air loaded with humidity, and it's a huge burden on your AC/dehumidifier.

If I decide to exhaust some of the air direct out of the fish room, then this air is going to be very humid as well, so the amount of transfer of humidity of the incoming air to the outide air may not be very great. But it should still be better than NONE at all.

As far as I can tell ERV's also have some type on humidty condenser and drip pan that uses the inside air to cool the outside air coming in to dehumidify it.

I dont believe that is the way the air is dehumidifed in an ERV. They seem to either use some dessicant material to absorb moisture or these resin-treated paper cores that transfer the moisture back and forth, but they do not have a drain or a drip pan. HRVs do have a drain, because in the winter the water condenses and then freezes in the unit, and they then need to go into defrost mode. ERVs wont freeze up (at least in the same way), because they dont collect water.

I know it would be much less effecient and my installers warn me that tthey ahve been told that an erv in the north will frost up and lock up without the hrv defrost module.

Less efficient? How so?
In the winter it will add a bit of humidity to the air coming in, so you might have to run it longer if your intent is to lower overall humidity. I guess in that sense it's true. But they dont need to go into a defrost mode either, which will lower the overall efficiency of the HRV because it needs to defrost the core every hour or so. Also, the ERV wont overdry the home as easily. Some people who install HRVs wind up with a humidifier soon afterwards. In all fairness, we have tanks so we probably wouldn't need one anyway.

But in the summer it would definitely be more efficient to run an ERV (if you even plan to use this type of ventilation in the summer) because the air you bring in wont be so loaded with humidity since some portion should get transfered to the outgoing.

A plate type or HRV would be best suited for a fish room as we are typiclly trying to get rid of moisture from these spaces.

But if you use this in the summer, the air you bring in from outside may very well have the same or more humidity than the air you are pulling out of your house or fish room. Again in the winter this may be true to some extent. But again because of the defrost mode of HRVs, the efficiencies may be much more similar than you think.

[wmilas]

Originally posted by tinytool
Is this model considered an ERV? The price on it seems much lower than the other models I've researched but it claims it is an Air Exchange ventilator


http://www.rewci.com/faairexveae.html

This is neither an ERV or a HRV but the much simplier ARV.. basicly its just a machanized vent. a HRV has to have a defrost unit... So you can pinpoint a HRV on that fact alone.

[wmilas]

I am providing a lot of ERV information, because I keep getting bombarded with "HRV-HRV'HRV" on the boards, whereas in talking to people out in the field, I get a mixture of responses. I actually havent decided between the 2 for certain yet. [/B]

Where do you live? If its in the north your decision is already made for you...

[wmilas]

Originally posted by johns
OK. I'm finally collecting my thoughts here. I'm still waffling back and forth between HRVs and ERVs, but here are few more points.

Both HRV and ERV's exchange air. If the outside air is more humid than the inside air (it will be in teh south) then its impossible the for the air exhange to lower the humidity in the house.

This is true. But if are going to use this type of ventialtion in the summer, an ERV is still the better choice. That way the VERY humid incoming air from outside can at least transfer part of it's humidity to the outgoing air. That is why many poeple who have HRVs wont run them in the summer. You'd be bringing in air loaded with humidity, and it's a huge burden on your AC/dehumidifier.

If I decide to exhaust some of the air direct out of the fish room, then this air is going to be very humid as well, so the amount of transfer of humidity of the incoming air to the outide air may not be very great. But it should still be better than NONE at all.

This is true. So the question is what do you do in the summer?

1) Run the HRV. If the air you are exhausting is more humid than outside you are a winner. Except for 2 months here in Chicago this will be the case for me. For the 2 months where it is iffy I plan to open the intake in the fishroom wide open to pull as much out as possible. I havent run it yet (it just was put in) so I'm not sure how well this is going to work.

2) Run a seperate blower out of the fishroom. The problem here is that you will create a vacuum in the house doing this and you WILL pull in humid air from cracks, vents ect throught the house. You lower the humidity in the fish room but increase the humidity in the rest of teh house. THATS why I did not want to put a vent in the fishroom to blow out humidity. It works for a spot humidity reducer but overall in the winter it sucks in cold air and in the summer sucks in hot air... energy wise its a killer.

3) Run a dehumidifer in the 2 months that the HRV is iffy. I plan to do this. I bought a very effecient LG 50 gal/day humidier that I've plumbed into the drain. Its pretty quiet and really energy effecient for spot dehumidying.

4) Humiditrol (Lennox) or any other furnace stack dehumidier. Its whole house and is suppsed to remove 75 gals or more a day. I'm leaving this option open. If I was in the south I'd do this in a heartbeat. I don't need it in the winter. I put oversized coils on my AC units so I should be dehumidifying off that plus the spot dehumidifer in the fish room. If I still can't control it I'll put one of these in.

5) Install an ERV alongside the HRV for the summer months. This option, quite frankly, sucks. Its expensive, and the plumbing is a nightmare. It already is a jumble of 6 inch pipes going every which way with the HRV/HVAC/Hepa combo. Throwing a ERV in would be silly complicated.

As far as I can tell ERV's also have some type on humidty condenser and drip pan that uses the inside air to cool the outside air coming in to dehumidify it.

I dont believe that is the way the air is dehumidifed in an ERV. They seem to either use some dessicant material to absorb moisture or these resin-treated paper cores that transfer the moisture back and forth, but they do not have a drain or a drip pan. HRVs do have a drain, because in the winter the water condenses and then freezes in the unit, and they then need to go into defrost mode. ERVs wont freeze up (at least in the same way), because they dont collect water.

I simply dont know here. I know it dehumidifies. It may be the case it jsut transfers humdity between streams as stated.

I know it would be much less effecient and my installers warn me that tthey ahve been told that an erv in the north will frost up and lock up without the hrv defrost module.

Less efficient? How so?
In the winter it will add a bit of humidity to the air coming in, so you might have to run it longer if your intent is to lower overall humidity. I guess in that sense it's true. But they dont need to go into a defrost mode either, which will lower the overall efficiency of the HRV because it needs to defrost the core every hour or so. Also, the ERV wont overdry the home as easily. Some people who install HRVs wind up with a humidifier soon afterwards. In all fairness, we have tanks so we probably wouldn't need one anyway.

But in the summer it would definitely be more efficient to run an ERV (if you even plan to use this type of ventilation in the summer) because the air you bring in wont be so loaded with humidity since some portion should get transfered to the outgoing.

The net loss in heat in the winter is why it would be less effecient for me. I'll get in the mid 70% energy exchange on the HRV where i'd lose all that with the ERV. That adds up to alot of energy. Yes the HRV has to defrost but that defrost is rolled into the 70% number. The HRV WILL overdy my house.. of that there is no doubt. I've also installed a large powered Humdifier (my house has alot of hardwood and you need humidity or things go horribly wrong). How much it'll have to run I'm not sure yet.

I've been told you set the HRV's run frequency manually. You set the humidity parameters.. say low 30% high 45%. The HRV runs normally but stops venting if it hits 30% and waits for the humidifier inhouse to catch up. if it hits 45% it runs the HRV longer. Ontop of that you have an inside and outside humidity probes that slides this range around so as to not for up the windows in the winter with too much humidity ect. It'll be interesting to see how well this all works. The guys putting it in have never installed the complete package with the controller logic so I'm not sure what to expect. Most people just put in an hrv, manually set it on low, and leave it alone and never touch it (except to maybe turn it off int eh summer months). I'd rather have the logic installed for optimum humidity, fresh air exchange, and (hopefully) balanced house preasure.

A plate type or HRV would be best suited for a fish room as we are typiclly trying to get rid of moisture from these spaces.

But if you use this in the summer, the air you bring in from outside may very well have the same or more humidity than the air you are pulling out of your house or fish room. Again in the winter this may be true to some extent. But again because of the defrost mode of HRVs, the efficiencies may be much more similar than you think. [/B]

[/quote]

Bingo. The question is, how many months a year is the humidity outside higher for you? As stated above the fan method doesnt work during the summer (even though most people swear by it) because it creates a vaccum which jsut draws in moist hot air into the rest of teh hosue from cracks ect. I'm hoping a spot humidifier or whole house humidifier is going to help here.

I'll keep you posted on how this all works. The HRV is currently hooked up but some of the logic hasnt been installed yet.

[johns]

wmilas-

some good points, and also a few I dont quite agree with (or maybe I dont understand)

1) Run the HRV. If the air you are exhausting is more humid than outside you are a winner.

You should have a better chance of meeting these conditions with the ERV, and therefore may be able to run the ERV for a month or so longer than the HRV. Again, this is because you can partially dehumidify the incoming air.

The net loss in heat in the winter is why it would be less effecient for me. I'll get in the mid 70% energy exchange on the HRV where i'd lose all that with the ERV.

Dont understand this statement at all, and dont know where you are coming up with it. There is no reason the ERV would be less efficient at transferring heat in the winter. The efficiencies of most good units are pretty similar. The ERV will only lack some 'drying' capability in the winter in relation to an HRV. Other than the moisture difference, the actual amount of heat transfered between air streams should be very similar.

Anyway, I think I have pretty much concluded that either of these HRV/ERV will work. If you want to plan to use it longer and get the most out of it in the summer, (which is when I seem to have a huge humidity problem in the fish room) an ERV is a good choice. If you are really just interested in the winter and dont think you need to worry about over-drying your house, an HRV is a good choice.

[Double-J]

After reading this thread I decided that they are both effective and work towards the same goal (might be wrong) The big decision factor was the price for me, I couldn't find a ERV under $800 so I decided to go with a AIRVA HRV for about $450 after shipping. I just recieved it today and took about 2 hours to get it all hooked up. still have a little more to do but it is done for the most part. The build quality is outstanding. the thing is massive weighing about 70lbs. and is rated for 3000 sf at 100w. here are some pics:

[Double-J]

forgot to add... my fish room is always at a steady 50% humidity after 10 minutes of having this on it is already down to 42%. I hope it stays like this or gets better. for the summer months if this doesn't work I have my cold air return and vent in the fish room which seems to help some.

[rayjay]

As I've had my HRV, a double cored unit, for several years now, I think I can add to this discussion.
First, my unit will not "overdry" my house because there is a control that shuts it down if humidity gets lower than what you set it for. I have no need for a humidifier with all the tanks I have.
Second, in the summer I run the A/C AND the HRV.
The warm, humid outdoor air is cooled in the cores by the cooler outgoing air from indoors and condenses the humidity from the incoming outdoor air.
The only time there is no condensation of either the incoming or outgoing air, winter or summer, is when the indoor air and the outdoor air are both the same temperature.

[steve the plumb]

what can I do if I have no vents in my basement(old home)I am stuck running a portable a/c unit.It gets very hot and humid in the summer.My garage is next to my basement where the tank is.There is a 4 inch hole in the garage door where the old dryer vent was.I am wodering if such a unit would work for me or is it better to get a deumidifer(stand alone type)I have one but it heats up the room so its a catch 22.Humidity is very high in summer.Winter isn't a problem

[DarthBaiter]

What would something like this be considered?
http://www.humidexhome.com/index.cfm
Even before I had my tanks, I always had a musty humid basement. My friend who also had this problem installed one of these and he can't stop raving about it.

[maro1]

Tiny tool

How is your AIRVA HRV working now?

Mar

[Double-J]

I tore down my tank preparing for my 380 gallon so at the moment only have about 150gallons of water and and some t5's over my prop tank so the humidity isn't an issue especially with it being cold outside. I do have it running on fullblast in the room with the door open and I don't notice it being colder in the basement than the rest of the house so it is definitely exchanging. The only problem I'm facing at the moment is the HRV is in a closet with my Home theater componants and a couple of computers that run 24/7 so It builds condensation on the intake side of the unit. I have a paintray that catches it now until I make something more permanent that will drain down into the sewer pipe. I can't say enough about the unit it is very well built. I'm sure it will serve it's purpose when I get my tank up and running.

[maro1]

Tinytool, where did you buy your Arriva unit and what model did you get?

I have a 300 gal unit and if I keep my thermostat turned down it runs 70% humidty in my basement WOW... I need to fix this quick.


Mar