ERV install that I'm unsure about
Hello, I'm planning to install ERV in the house I'm in the process of building. I'm pretty comfortable with doing ductwork myself. I'm just not too familiar with design. With the help with AI I figured I'm going for 160 CFM Broan ERV for 1900sq ft house and go with 6 inch round duct as it comes out of the ERV then I'm thinking to go to like a 12 inch buffer and go to 5 inch runs to each room for supply and returns to bathrooms. I'm going to install registers up on the wall high and run everything through joists in the ceiling and trusses. The house is very insulated and tight so it's not going to be cold or hot near the roof. Also installing a air pre heater as I'm in the very cold zone.
- I'm guessing I should just insulate the air duct coming in from the outside?
- AI seems to thing that I should not go lower duct size then 5 inch. Wondering if anyone has other ideas. I've seen Broan drawings where it steps down the size every time the duct splits.
- AI also seems to think that I also need to put a air buffer that will distribute the air to all the runs. Does it seem right?
- Not sure how the air preheater will be connected and work with the ERV
Wondering if I'm missing something?
Comments
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Outside connections are at the same temperature as outside air so without insulation you'll get condensation and frost on them. Make sure you install all of it seal the vapor barrier sleeve to the unit and to wall cap.
You'll need at least 6" ducts for that much airflow. Also want a length of flex or an inline silencer (I'm assuming that is what you mean by buffer) to reduce noise between the unit and the main trunk. These units are quiet but without something, you'll notice when it goes on boost.
Bed flows are 10-20CFM. You can do that with 3" duct but go for 4" to reduce noise. A lazy S bend of flex on each bed supply is good for acoustic isolation between bedrooms.
Stale air pickups are usually more. You want about 50CFM per bath and a larger say 65CFM pickup near the kitchen. Bath pickups can be 5" kitchen, 6".
That ERV has a recirc defrost, it doesn't need a pre-heater. If you are in very cold climate, the supply air will be colder than room air which might create comfort issues. In that case, you can install the heater in the supply duct and set it to maintain 70F. You can avoid this issue if you connect the fresh air supply to your HVAC air handler return as it can condition the supply air.
Important bits.
Put the unit where it can be easily serviced to swap filters. Even better install an insulated filter box on the outside air intake that takes a larger filter. This avoid the cost of the expensive OEM filters and last longer.
I find I use the boost switch in the kitchen more than for bath, a 2h or 4h push button timer is a good way to clear the house after cooking up a storm. For bath boost control motion activated switch is the simplest as you don't have to think about it.
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For 160 CFM 7" round and that is pushing it a little
Normally
6" round 100 cfm
7" 150
8" 200
5" 60cfm
If you use flex duct it should be larger. If you don't go large enough you will restrict the airflow
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Where is this house located?
ERV's are fine in dry cold climates but are poor in warm damp climates.
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They also work in warm damp climates as they reduce the amount of humidity brought in.
HRV is a good choice if you are in a climate with dry outside air in the summer and also have high indoor humidity (some places in the PWN). In this case, the HRV will help reduce indoor humidity.
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ERV'S and HRV'S do not reduce RH. Whatever the outside RH is, is what gets delivered to the structure.
Only a dehumidifier or A/C can reduce RH.
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HRVs bring the air stream temperatures towards equilibrium. As the air streams pass by each other in the core, the warmer one gives up heat to the cooler one. The humidity remains unchanged.
ERVs do the same, plus moisture. The air streams pass through a rotating core, heat, moisture (and, alas, VOCs) are absorbed by the media/coating of the rotating core from one air stream and are released into the other as it moves through the other air stream.
Both of these processes are driven by the difference in heat/RH, they simply goes from high to low. the transfer is basically backwards in summer vs winter.
Heating increases the amount of moisture that can be held in the air, thus reducing the RH (Relative Humidity)—but not the amount of water in the air.
Cooling (past the dew point!) will condense moisture out of the air and, assuming the water makes it into the drain and leaves the building envelope, will lower the amount of water in the air. The RH of the air leaving the AC, however, will be at 100ish%; at least until the air warms up a little (see heating above).
A dehumidifier combines both, the air leave the unit will be both dryer (and warmer) than it entered.
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Thanks for your tips! sorry it took me a while to answer. Had issues with internet. The unit will be very accessable in a mechanical room. I'm definitely going to insulate the air intake from the outside but what do you mean by vapor barrier. not sure what needs to be done. Can you elaborate?
its in Jackson, wy so it gets down to -30 sometimes.
I'm not looking to reduce RH. It's pretty dry climate here.
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