I have a x24ERV from venmar installed in a house where the blower door test measured about 0.3 ACH50. The house is really air tight.
I know that the fan tables with the unit provide a way to measure air flow across the core to facilitate balancing fresh and stale air flows.
my installer and I have both independently attempted balancing using a digital differential manometer with funny results. we can easily balance the machine air flow according to the manufacturer's specification within a couple of percent.
I have an anemometer and a hood and have measured the air flows from the rooms and verified that they are close to the air flows measured across the core.
I have also used the anemometer to do an 50 point average across the width and depth of the vent hood outside on the fresh and stale supply and have verified that they are practically the same as using the static pressure measurements accross the ERV core.
The issue is, with the machine's air flow balanced, the house is actually under negative pressure. To verify this, on a still day I have opened a window and taped the gap to creat an air tight diaphram around the window. I puncture a hole in the tape and insert one of the manometer tubes through the hole so it is hanging outside.
The pressure reads negative. If i put the machine in recirculate, the negative pressure dissappears as expected. As soon as I turn back to continious ventilation, the pressure becomes negative despite the air flows being “balanced”.
I have not been able to find any leaks on the exhaust or supply from the unit to the outside.
I was unaware that there was a balancing issue until smoke from the chimney trickled into the living space while lighting the stove. I realized what was going on quite quickly and opened the windows and the smoke stopped trickling through the joints. When the stove is not lit and the air flows of the unit are balanced
I can feel cool air trickling into the living space through the chimney joints. Venmar says that their tables are for a closed system. I am thinking that the ventilator and house aren’t really a
closed system since the house is really like a plenum with air flowing through it. any plenum, like a house for example has leaks. There is no way to prevent air from being drawn or expelled through those holes since they are part of the
plenum and hence a part of the static pressure associated with the duct system.
Anyway, when I unbalance the system(on a still day, with a slightly open window taped around like a diaphram and one manometer tube placed outside through a hole in the tape) I can balance the negative pressure of the house and I no longer feel air coming from around the chimney joints. The issue is that I have to unbalance the machine significantly (ie 100 cfm Supply, 70 cfm exhaust), in order to achieve the pressure balance. Because the unbalancing is so extreme it is affecting the moisture exchange dramatically and the house humidity is always above 55% and that is mostly maintained by keeping a dehumidifier going now that we are in the cold season. So the stove issue has been fixed but unbalancing the unit has affected the rate of moisture recapture through the core.
Does anybody have any thoughts as to what may be happening? If the machine is balanced, why is the house experienceing negative pressure? Is it because of the duct runs, air moving and differenty speeds through them and therefore the static pressure conditions of the supply and return not being matched? I thought this may be the case but I decided to switch the exhaust and intake at the hoods as well ast the supply and return on the unit. Each time I balance I see the same result. Based on this, I am convinced that the problem has some fundamental physics involved. My experience with air handling and ducts is fairly rudimentary although I have quite a bit of physics knowledge.
I am thinking that it could be explained with a simple model where a supply fan in a duct connected to the outside is blowing air through a duct into a leaky plenum (the house) and another independent fan pulls exhausts air out of the plenum to the outside. I know in real life it is more complicated. I am also thinking that the effect we are seeing is somewhat due to the air tightness of the house and in most houses the pressure would equilibrate quickly since tightness would be 10 time worse than this house.
DJG.
I know that the fan tables with the unit provide a way to measure air flow across the core to facilitate balancing fresh and stale air flows.
my installer and I have both independently attempted balancing using a digital differential manometer with funny results. we can easily balance the machine air flow according to the manufacturer's specification within a couple of percent.
I have an anemometer and a hood and have measured the air flows from the rooms and verified that they are close to the air flows measured across the core.
I have also used the anemometer to do an 50 point average across the width and depth of the vent hood outside on the fresh and stale supply and have verified that they are practically the same as using the static pressure measurements accross the ERV core.
The issue is, with the machine's air flow balanced, the house is actually under negative pressure. To verify this, on a still day I have opened a window and taped the gap to creat an air tight diaphram around the window. I puncture a hole in the tape and insert one of the manometer tubes through the hole so it is hanging outside.
The pressure reads negative. If i put the machine in recirculate, the negative pressure dissappears as expected. As soon as I turn back to continious ventilation, the pressure becomes negative despite the air flows being “balanced”.
I have not been able to find any leaks on the exhaust or supply from the unit to the outside.
I was unaware that there was a balancing issue until smoke from the chimney trickled into the living space while lighting the stove. I realized what was going on quite quickly and opened the windows and the smoke stopped trickling through the joints. When the stove is not lit and the air flows of the unit are balanced
I can feel cool air trickling into the living space through the chimney joints. Venmar says that their tables are for a closed system. I am thinking that the ventilator and house aren’t really a
closed system since the house is really like a plenum with air flowing through it. any plenum, like a house for example has leaks. There is no way to prevent air from being drawn or expelled through those holes since they are part of the
plenum and hence a part of the static pressure associated with the duct system.
Anyway, when I unbalance the system(on a still day, with a slightly open window taped around like a diaphram and one manometer tube placed outside through a hole in the tape) I can balance the negative pressure of the house and I no longer feel air coming from around the chimney joints. The issue is that I have to unbalance the machine significantly (ie 100 cfm Supply, 70 cfm exhaust), in order to achieve the pressure balance. Because the unbalancing is so extreme it is affecting the moisture exchange dramatically and the house humidity is always above 55% and that is mostly maintained by keeping a dehumidifier going now that we are in the cold season. So the stove issue has been fixed but unbalancing the unit has affected the rate of moisture recapture through the core.
Does anybody have any thoughts as to what may be happening? If the machine is balanced, why is the house experienceing negative pressure? Is it because of the duct runs, air moving and differenty speeds through them and therefore the static pressure conditions of the supply and return not being matched? I thought this may be the case but I decided to switch the exhaust and intake at the hoods as well ast the supply and return on the unit. Each time I balance I see the same result. Based on this, I am convinced that the problem has some fundamental physics involved. My experience with air handling and ducts is fairly rudimentary although I have quite a bit of physics knowledge.
I am thinking that it could be explained with a simple model where a supply fan in a duct connected to the outside is blowing air through a duct into a leaky plenum (the house) and another independent fan pulls exhausts air out of the plenum to the outside. I know in real life it is more complicated. I am also thinking that the effect we are seeing is somewhat due to the air tightness of the house and in most houses the pressure would equilibrate quickly since tightness would be 10 time worse than this house.
DJG.
