Bruce Breedlove
11-15-2009, 02:19 AM
As I noted in another thread or two, I recently inspected a building that was once a Welcome Center for a developer and was later donated to a church and moved to its present location. (The property also included a Quanset hut.)
Due to the large number of occupants during church services additional fresh air was required to maintain indoor air quality in this building. An HRV (Heat Recovery Ventilator) was installed to supply this fresh air.
For those that are not familiar with HRVs (and the close cousin the ERV - Energy Recovery Ventilator), an HRV is essentially a heat exchanger that recovers heat that otherwise would be lost in the ventilation process. HRVs are usually 60% to 80% efficient. The air flow in equals the air flow out so the building is not pressurized or depressurized by the HRV.
In a heating environment (such as Colorado) 60% to 80% of the heat in the inside air that is exhausted is picked up by the cooler outside air being brought into the building. The outside temperature here today was 30 degrees. With the indoor air at 70 degrees, after passing through the HRV the 30 degree outside air would be heated to somewhere around 55 or 60 degrees. The higher temperature of the fresh air will reduce the operating time of the furnace and reduce the utility bill.
I do not typically inspect HRVs during a home inspection but I noticed something odd about the one in the church. The two registers in the room were fairly close together and I thought they might short circuit so I turned on the HRV to find out. One register should have been a supply and the other should have been an exhaust. I was surprised to find that both registers were blowing 30 degree air into the room. When I checked the two outside grilles they were both drawing air in.
So, the HVAC contractor installed the HRV incorrectly. With both intakes located outside there is no exchange of heat. The HRV has now become a giant intake fan that delivers twice the intended CFM, pressurizes the building and causes a tremendous loss of energy while making the building very uncomfortable.
The preacher said the HRV moved too much air and made the room cold in the winter. Now I think I understand why he said he didn't like to run the HRV.
Due to the large number of occupants during church services additional fresh air was required to maintain indoor air quality in this building. An HRV (Heat Recovery Ventilator) was installed to supply this fresh air.
For those that are not familiar with HRVs (and the close cousin the ERV - Energy Recovery Ventilator), an HRV is essentially a heat exchanger that recovers heat that otherwise would be lost in the ventilation process. HRVs are usually 60% to 80% efficient. The air flow in equals the air flow out so the building is not pressurized or depressurized by the HRV.
In a heating environment (such as Colorado) 60% to 80% of the heat in the inside air that is exhausted is picked up by the cooler outside air being brought into the building. The outside temperature here today was 30 degrees. With the indoor air at 70 degrees, after passing through the HRV the 30 degree outside air would be heated to somewhere around 55 or 60 degrees. The higher temperature of the fresh air will reduce the operating time of the furnace and reduce the utility bill.
I do not typically inspect HRVs during a home inspection but I noticed something odd about the one in the church. The two registers in the room were fairly close together and I thought they might short circuit so I turned on the HRV to find out. One register should have been a supply and the other should have been an exhaust. I was surprised to find that both registers were blowing 30 degree air into the room. When I checked the two outside grilles they were both drawing air in.
So, the HVAC contractor installed the HRV incorrectly. With both intakes located outside there is no exchange of heat. The HRV has now become a giant intake fan that delivers twice the intended CFM, pressurizes the building and causes a tremendous loss of energy while making the building very uncomfortable.
The preacher said the HRV moved too much air and made the room cold in the winter. Now I think I understand why he said he didn't like to run the HRV.