Author Topic: HRV vs. ERV (or both)?  (Read 3655 times)

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jlsoaz

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HRV vs. ERV (or both)?
« on: January 16, 2020, 03:03:36 PM »
Hi - does anyone have strong views on HRV vs ERV for achieving goals of both fresh healthy air in a residence (or commercial building) along with not using more energy than needed to keep the air at a comfortable temperature?    Generally this is seen as a question of which climate a person is in, no?

I'm at 3500 feet altitude, and there are wide swings in temperature.  Even though generally this is a very hot area in summer (Arizona), I find myself expending a lot of energy to keep the place warm in winter.  Is there such a thing as having both types of unit installed, and then switching between them, depending on the season?

DamonHD

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Re: HRV vs. ERV (or both)?
« Reply #1 on: January 16, 2020, 03:48:53 PM »
In the UK ERV is considered rarely necessary, where you are moreso:

https://forum.buildhub.org.uk/topic/12734-no-condensate-from-mvhr/?tab=comments#comment-213746

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bigrockcandymountain

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Re: HRV vs. ERV (or both)?
« Reply #2 on: January 16, 2020, 05:12:38 PM »
Ok so here is my experience.

I have an ultimate air 200dx ERV and I have just ordered a Venmar e15 ecm HRV to replace it.

It is about -10f.  -25 celsius here and has been for the last week.  We are having trouble keeping the humidity down.  It is around 50% and sometimes 60%.  In your climate, i think an erv would be fine, but not here.  (Saskatchewan, Canada)

We are also off grid so we don't like to run the erv wide open for long periods.  It is always on though and doesn't use much power.  It is amazingly efficient at heat transfer.  I am expecting the hrv to be a little less efficient that way. Our house is passive house airtight and we are a family of 4 always cooking, showering etc.

The people that sell hrv / ervs like to make it seem simple but it really depends on a lot of factors.  Namely, your climate, your airtightness of your envelope, and the habits of the people living in the house. 

I will add that the ultimate air erv works differently than most erv's.  I believe it returns more moisture than other erv's.
 
If anyone wants a good used Ultimate Air 200dx ERV i will be selling mine.  They are a good unit, just not for our situation. 

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #3 on: January 17, 2020, 01:29:36 PM »
Thanks for the responses so far, very much to the point. 

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #4 on: January 17, 2020, 01:35:20 PM »
Ok so here is my experience.

I have an ultimate air 200dx ERV and I have just ordered a Venmar e15 ecm HRV to replace it.

It is about -10f.  -25 celsius here and has been for the last week.  We are having trouble keeping the humidity down.  It is around 50% and sometimes 60%.  In your climate, i think an erv would be fine, but not here.  (Saskatchewan, Canada)

We are also off grid so we don't like to run the erv wide open for long periods.  It is always on though and doesn't use much power.  It is amazingly efficient at heat transfer.  I am expecting the hrv to be a little less efficient that way. Our house is passive house airtight and we are a family of 4 always cooking, showering etc.

The people that sell hrv / ervs like to make it seem simple but it really depends on a lot of factors.  Namely, your climate, your airtightness of your envelope, and the habits of the people living in the house. 

I will add that the ultimate air erv works differently than most erv's.  I believe it returns more moisture than other erv's.
 
If anyone wants a good used Ultimate Air 200dx ERV i will be selling mine.  They are a good unit, just not for our situation.

Hi - thanks for running through these points.   Some things here for me to think about.  I guess I'll need to try to understand the humidity points better.  I'm in an area where people usually go for ERV, but I'm told by the concrete dome builders that de-humidification is more something they emphasize, so I'm not sure that fits with my getting something that might make it more humid inside.  Also, when buying coolers around here, over the years folks have opted for air conditioning or evaporative coolers.  One of the reasons the EVAP coolers have somewhat lost the battle is they do not work when it gets humid.  Around here they work most of the time, but once in awhile it is rainy and then they don't work.

The tight envelope of your passive house sounds a bit similar to mine.  I think my main question for you would be whether there is such a thing as retaining your ERV and running it some of the time, but then switching over to HRV for other times.  Temps here range from over 100 or 105 F in summer to a bit below (not sure exactly how much) 32 F in winter.  Within a day, there can be a (somewhat) wider swing than some folks are accustomed to, as one might expect in (somewhat) high desert.  These are temps in formally reported terms, but then I tend to see slightly different temps if checking other sources, such as occasionally seeing 110 F on my car dashboard.

bigrockcandymountain

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Re: HRV vs. ERV (or both)?
« Reply #5 on: January 17, 2020, 02:19:03 PM »
I guess the question i would ask is, what problem exactly are you trying to solve with a ventilation system? Do you have higher humidity than you would like?

Is your air quality poor? What type of heat system do you have?

My experience with the 200dx may not be applicable to all ervs either.  I will try to explain...

The 200dx uses an enthalpy wheel.  When it is colder outside than inside, the wheel material causes the moisture in the outgoing air to condense on the wheel, make half a revolution, and then re evaporate into the incoming fresh air.  This potentially transfers all of the moisture.
 When there is no temperature difference, no condensation occurs, and it doesn't transfer much moisture at all.

Normal ervs use a semipermeable heat exchanger that is driven by difference in relative humidity. They can only really return half the moisture into the opposing air stream because after half is transfered, the rh is balanced and no transfer occurs.  I believe this leads to less moisture transfer than an enthalpy wheel type, especially in a very cold climate. 

Hrv's transfer no moisture at all. 

Having both is not a bad idea, but space is limited, so i will try the hrv only and see how that works. 


jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #6 on: January 18, 2020, 01:50:00 PM »
I guess the question i would ask is, what problem exactly are you trying to solve with a ventilation system? Do you have higher humidity than you would like?

Is your air quality poor? What type of heat system do you have?

My experience with the 200dx may not be applicable to all ervs either.  I will try to explain...

The 200dx uses an enthalpy wheel.  When it is colder outside than inside, the wheel material causes the moisture in the outgoing air to condense on the wheel, make half a revolution, and then re evaporate into the incoming fresh air.  This potentially transfers all of the moisture.
 When there is no temperature difference, no condensation occurs, and it doesn't transfer much moisture at all.

Normal ervs use a semipermeable heat exchanger that is driven by difference in relative humidity. They can only really return half the moisture into the opposing air stream because after half is transfered, the rh is balanced and no transfer occurs.  I believe this leads to less moisture transfer than an enthalpy wheel type, especially in a very cold climate. 

Hrv's transfer no moisture at all. 

Having both is not a bad idea, but space is limited, so i will try the hrv only and see how that works.

Hi - thanks for the answers.

To answer your question, I'm trying to achieve significantly improved air quality (lower CO2) while also maintaining moderate energy usage.  My home is extremely tight, and the only ventilation I really have is with a couple of bathroom fans and one or two other openings.  The split-zone mitsubishi heat pump provides good efficient heat and a/c but not ventilation (unless I am misreading).
https://www.mitsubishicomfort.com/sites/default/files/manual/msz-fe18-operationmanual.pdf?fid=291

The home has no gas-burning combustion going on for cooking or heating, but the ventilation has been so inadequate that air quality has still been a concern.  Recently I finally got more on top of the two bathroom fans, and according to some co2 sensors, the air quality has improved.  However, this has also taxed the heating system a bit, since I am ventilating a lot of heated air to the roof.  So, I'm thinking I could restore a bit of the energy-saving approach to things in the home, while at the same time bringing modern technology to bear in ventilation (rather than just cracking a window or two open and turning on the bathroom fans).

This is the type of home:
https://www.terra-dome.com/
you can see that the builder tends to recommend some ventilation/de-humidification focus:
https://www.terra-dome.com/links
https://www.thermastor.com/

so even though I'd be ok with some humidity, I'm not anxious to go in that direction if I don't have to (in addition to the fact that I am wary of what happens when it is very humid outside, which happens once in awhile).

another question comes to mind: do some ventilation systems come with the ability to interact smartly with an internal CO2 sensor and turn on and off depending on the measured indoor air quality?

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #7 on: January 19, 2020, 01:25:01 AM »
I also belatedly realized another question: is an ERV or HRV supposed to be used as stand-alone heating/cooling?  Or is it meant to be used in conjunction with some other heating/cooling units.  I've been focusing on it for ventilation.

DamonHD

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Re: HRV vs. ERV (or both)?
« Reply #8 on: January 19, 2020, 03:59:12 AM »
HRVs can be stand-alone just for ventilation or can include (for example) an inline heater for when peak heat demand is very low (eg in a Passive House).

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bigrockcandymountain

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Re: HRV vs. ERV (or both)?
« Reply #9 on: January 19, 2020, 07:11:28 AM »
They are meant to be stand alone ventilation.  They do not heat or cool at all.  As damon says, an inline duct heater after the hrv can be used, but your heat pump will be much more efficient.


jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #10 on: January 21, 2020, 02:30:01 PM »
OK, thanks again.

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #11 on: January 28, 2020, 11:49:00 AM »
We decided on this unit:

https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/energy-recovery-ventilators/intelli
Intelli-Balanceā„¢ 100 Balanced Air 50 - 100CFM

Some have advised that noise can be an issue, and I"m still not quite sure what to make of the humidity questions that come up, so if anyone has any advice about where to locate it or other installation points, please let me know.  We haven't finalized the location where it will go, but I don't have an attic.  I may have to drill another hole or two in the concrete.

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #12 on: February 11, 2020, 08:36:36 PM »
I'm watching this video:

https://www.youtube.com/watch?v=pkvoXK6-fjk

but can anyone comment on:

a) best placement of the ERV?  (My installer, not having dealt with them much, was somewhat inclined to installing outside.  Can such a thing be done?  I'm doubting it.  He said he would ask).
b) do the intake and the outgoing air vents need to be set apart from each other?

DamonHD

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Re: HRV vs. ERV (or both)?
« Reply #13 on: February 12, 2020, 02:36:48 AM »
I would certainly separate the external vents (inlet and outlet) as much as you reasonably can, point them in different directions, and arrange that the prevaling wind direction takes outlet air away from the inlet.

But maybe I misunderstood you?

Rgds

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southpaw

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Re: HRV vs. ERV (or both)?
« Reply #14 on: February 12, 2020, 07:18:19 AM »
I have never seen an hrv or erv certified for external installation. The installation manual will tell you if it's possible but I highly doubt it. The manual will also tell you the minimum separation of the air inlet and outlet. There will be a concentric vent option which uses the same hole for both which would be a good choice in your situation. If you built a weatherproof enclosure on th exterior you could probably install it there. I've seen a lot of houses in your area with water heaters sitting outside with little or no protection and I'm sure they're not certified for the exposure. By the book is best.

bigrockcandymountain

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Re: HRV vs. ERV (or both)?
« Reply #15 on: February 12, 2020, 08:14:16 AM »
Both of mine have been 6' minimum separation of intake and exhaust ducts. 

The unit must be mounted indoors. 

I ducted to pull stale air from bathrooms and bedrooms and supply fresh air to living room and kitchen.
It is more normal to exhaust from bathrooms and kitchen and supply fresh to bedrooms and living rooms.


jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #16 on: February 16, 2020, 03:35:06 PM »
all of the recent answers seem helpful, thanks, I am going to forward them verbatim to my installer.

jlsoaz

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Re: HRV vs. ERV (or both)?
« Reply #17 on: April 05, 2020, 03:43:21 PM »
present status is
- the installer who put in my two bathroom fans wasn't into installing the ERV.
- After checking with about 5 or 6 more HVAC places over the next several weeks, one of them has agreed to come to the house and have a look and measure things and plan out the project to install ERV.  They are about 60-70 miles away, but that's kind of the way it goes around here.  Their visit will probably not take place for a few more weeks due to sarscov2 (more my concern than theirs, apparently).
- an interesting comment made by the new installer: they do not have a huge amount of experience with ERV, but I think sometimes have installed.  When we were reviewing my situation, as soon as I told them I had the type of system I have (minisplit that includes no ventilation that I'm aware, and a very tight house), they said that kind of explained my questions and it made more sense to them I was interested in ERV.