HVAC folks--- HRV/ERV systems

[IndyIN]

I'm considering an ERV system for my home in Texas and wanted to see if anyone has experience with them (or HRVs)? My home is a year old and pretty airtight. When I lived back in Indiana, my home was almost 20 years old (i.e. not as airtight), and the opportunity to open windows was much higher.


It is just plain hot in Central Texas, and AC is precious, which is what has me considering an ERV. They look straight forward enough as far as operation, but any real-life pros and cons are greatly appreciated.


For those wondering what an ERV is, it stands for energy recovery ventilator. Its goal is to turn over inside air with fresh outside air while conditioning it a bit in the exchange process.

 

[ChristianPatriot]

Energy recovery systems are almost exclusively used on large commercial/industrial applications that require a high volume of ventilation. Unless your house needs that much fresh air for some reason, you’re much better off getting a properly sized unit for your house.

 

[churchmouse]

CP nailed it. Not sure what your house is configured like as in single story ranch or 2 story's.
Some 2 story homes require 2 systems too achieve a comfort level all through the house.
Do it right when you do it.

 

[ChristianPatriot]

CP nailed it. Not sure what your house is configured like as in single story ranch or 2 story's.
Some 2 story homes require 2 systems too achieve a comfort level all through the house.
Do it right when you do it.

My house is probably getting a second system for the upstairs before next summer. 3,000 sq.ft. and two stories does not make for good comfort.

 

[churchmouse]

My house is probably getting a second system for the upstairs before next summer. 3,000 sq.ft. and two stories does not make for good comfort.

Shout out if you need any help.

 

[IndyIN]

I admit that I do not know much about HVAC, and I'm not sure I understand the properly sized unit comment. I do not have a problem cooling or heating my home, so I'm not quite sure I'm tracking unit size being my focus.


My reason, and the reason I understand that ERVs are used in residential, is for air quality not to help with cooling. I have a decent size home (2 stories and little over 5000 sq/ft with 2 units) that has been foamed and made to be pretty energy efficient. I think the idea of an ERV is to get a reasonable amount of air turn over in an efficient house. A not so tight house would do this through normal air leakage from what I've read.


ERVs seem to be relatively common down here and are not too expensive. They sound like they might be unicorns back in Indiana, though.

 

[ChristianPatriot]

I admit that I do not know much about HVAC, and I'm not sure I understand the properly sized unit comment. I do not have a problem cooling or heating my home, so I'm not quite sure I'm tracking unit size being my focus.


My reason, and the reason I understand that ERVs are used in residential, is for air quality not to help with cooling. I have a decent size home (2 stories and little over 5000 sq/ft with 2 units) that has been foamed and made to be pretty energy efficient. I think the idea of an ERV is to get a reasonable amount of air turn over in an efficient house. A not so tight house would do this through normal air leakage from what I've read.


ERVs seem to be relatively common down here and are not too expensive. They sound like they might be unicorns back in Indiana, though.

Proper sizing refers to the size of your house compared to the capacity of your units. A 1500 sqft house may need a 2-1/2 or 3-ton unit. Your house might have two 4-ton systems. If it’s maintaining temperature and humidity correctly, which it sounds like yours is, then it’s sized well enough.

The way an EVR systems works is: There is an exhaust side that pulls air out of the house and a fresh air intake side that pulls in fresh air from the outside. “Fresh” air also means hot air. Basically your blowing 72-75 degree air out of your house in exchange for 95+ degree outside air. This WILL make your system work harder to maintain temperature. The energy recovery portion comes from the process of using some kind of heat recovery wheel. The wheel continually rotates. There is a heat exchange process. The indoor air cools the wheel down and the outdoor air warms the wheel up. Vice versa in the winter. Basically it somewhat tempers the outdoor air temperature coming in. So say, for example, instead of straight 95 degree ambient temperature coming into your house, it’s 85 or 90 degrees. It’s “cooled” off by the wheel that was “cooled” off by having indoor air passed through it. No energy recovery system is perfectly efficient though. It does add an extra load to the house for the HVAC units to take care of.

If it’s a small enough amount of outdoor air, your HVAC system may not notice and continue to maintain temperature just fine. Too much fresh air will cause your system to not keep up.

Clear as mud?

 

[IndyIN]

Thanks for the detailed follow up. I really appreciate it. It sounds like the biggest downside to an ERV isn't really the ERV, but the likelihood that it exposes a marginally sized HVAC system that will go from just keeping up to not keeping up temperate wise.

 

[churchmouse]

Proper sizing refers to the size of your house compared to the capacity of your units. A 1500 sqft house may need a 2-1/2 or 3-ton unit. Your house might have two 4-ton systems. If it’s maintaining temperature and humidity correctly, which it sounds like yours is, then it’s sized well enough.

The way an EVR systems works is: There is an exhaust side that pulls air out of the house and a fresh air intake side that pulls in fresh air from the outside. “Fresh” air also means hot air. Basically your blowing 72-75 degree air out of your house in exchange for 95+ degree outside air. This WILL make your system work harder to maintain temperature. The energy recovery portion comes from the process of using some kind of heat recovery wheel. The wheel continually rotates. There is a heat exchange process. The indoor air cools the wheel down and the outdoor air warms the wheel up. Vice versa in the winter. Basically it somewhat tempers the outdoor air temperature coming in. So say, for example, instead of straight 95 degree ambient temperature coming into your house, it’s 85 or 90 degrees. It’s “cooled” off by the wheel that was “cooled” off by having indoor air passed through it. No energy recovery system is perfectly efficient though. It does add an extra load to the house for the HVAC units to take care of.

If it’s a small enough amount of outdoor air, your HVAC system may not notice and continue to maintain temperature just fine. Too much fresh air will cause your system to not keep up.

Clear as mud?

I have no real world experfience with the air loads of central Texas as in "Humidity" but here in the Hoosier state one of the big loads on the system is.....Humidity.

These are just big de-humidifiers presa and to overcome any air exchange would require more BTU capacity.

I have installed and serviced some serious ERV's on commercial and industrial facility's. I realize these are by comparison nothing like you would use on a residential system but just the "D" wheel is very complex in its operation.

Manufactured housing is a thing here. These are so tightly made that it is a requirement to have an air exchange. This also requires more capacity.

I am a firm believer in air turn over on any home/building/facility. That was a huge part of balancing loads in schools and closed buildings.

 

[jkaetz]

There's been a big thing made recently about doing air exchanges in new residential construction because they are sealed so well. https://www.epa.gov/indoor-air-qual...-do-i-need-my-home-improve-indoor-air-quality

I've seen many a discussion that for high humidity states like Indiana and, presumably, Texas suggesting a small whole home dehumidifier moving about 50 - 100 CFM with a fresh air intake to supply the air change. The theory is that the dedicated dehumidifier brings in the fresh air, drops the humidity, dumps it into the supply side of the HVAC, and pushes "stale" air out of the home through bathroom vents, appliance exhausts, etc... Bonus the dehumidifier will keep the humidity down when the temps are in the 70's+high humidity outside.

Our current home (built in 2012) uses a bathroom vent fan that runs (almost continuously) to pull in fresh air from wherever it can. Presumably it works but I've seen it suggested that this is a poor way to get air changes as it will pull the air in from wherever it can and it won't be conditioned at all.

 

[JettaKnight]

With modern homes, an ERV is a good investment in warding off all sorts of breathing / lung / sinus issues.


There's a reason you tell people to get plenty of fresh air to stay healthy.

And, in Texas, builders make homes tighter than they do in the Midwest.


I don't have any experience with ERV, but can you run it on a timer, such that it wouldn't adversely affect the AC during the noon day?

 

[ws6guy]

Not to high jack this thread but....how would you add a second A/C unit to a 2 story home where all of the ducts come off a main trunk line in the basement? I'd love to have a second A/C unit, on hot days the difference in temp from upstairs to main level is around 6-8 degrees different.

 

[ChristianPatriot]

Not to high jack this thread but....how would you add a second A/C unit to a 2 story home where all of the ducts come off a main trunk line in the basement? I'd love to have a second A/C unit, on hot days the difference in temp from upstairs to main level is around 6-8 degrees different.

Mine’s gonna have to go in the attic. New air handler with separate ductwork. Run the power and lineset. Set the unit outside near the other a/c condenser. Separate stat for upstairs.

 

[churchmouse]

Mine’s gonna have to go in the attic. New air handler with separate ductwork. Run the power and lineset. Set the unit outside near the other a/c condenser. Separate stat for upstairs.

Yup.

It is an entirely separate full system Stand alone from the downstairs unit.

 

[IndyIN]

With modern homes, an ERV is a good investment in warding off all sorts of breathing / lung / sinus issues.


There's a reason you tell people to get plenty of fresh air to stay healthy.

And, in Texas, builders make homes tighter than they do in the Midwest.


I don't have any experience with ERV, but can you run it on a timer, such that it wouldn't adversely affect the AC during the noon day?

The ERV that was recommended to me has a bit of a controller that you can configure how often to run per hour and throughout the day. Some recommend integrating them into the existing duct work and others recommend a completely separate run. I suppose either would work ok for my setup.

I lived my whole life in Indiana until moving to Texas in 2018 and there are certainly some things that are done differently down here. I have a Flir camera and I’m shocked how insulated and tight my home is.

 

[DocIndy]

Not to high jack this thread but....how would you add a second A/C unit to a 2 story home where all of the ducts come off a main trunk line in the basement? I'd love to have a second A/C unit, on hot days the difference in temp from upstairs to main level is around 6-8 degrees different.

If the basement isn’t finished and the duct is accessible, the supply duct could be resized to split the second floor from the first and a zone system added. The return still pulls from the whole house as usual, but a second stat on the second floor controls a motorized damper that separates the supply duct. Second floor calls, shuts the damper for the first floor and sends cooling to the second floor. A bypass damper bleeds off excess air back into the return. As anything HVAC related.... if installed and set up properly, they work extremely well.