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Properly balanced ventilation system

IRFL | Posted in Mechanicals on

Concerning a one year old home with all above grade walls and roof sheathing insulated with open cell spray foam and basement interior foundation insulated with closed cell spray foam insulation. Two ERV’s with the exhaust from the bathrooms and the fresh air supply connected to the air handles return. With the air ERV’s and handler fan on the house is under a negative 5.5 pascal pressure measured on the first floor with respect to the outside.

Question: What would be the recommended indoor pressure with respect to the outside. “0” ??. Is there a ERV or HRV available with individual fan speed to balance the house pressure to the desired level?

The home owner is exercising some odor from the foam insulation etc. and would a slight positive pressure be recommended to avoid/reduce the odor.?

Thanks

Flemming

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Flemming,
    What is your location or climate?

    Why do you have two ERVs? Is it a very big house?

    Most ventilation experts recommend that an ERV or an HRV should be installed with balanced supply and exhaust air flows. Balancing the flows should be a standard part of the installation and commissioning process. If the installer failed to balance the units, call the installer and discuss the issue.

    It's worth pointing out that when ERVs are connected to a forced-air system (instead of installed with dedicated ventilation ductwork), all kinds of energy use, air flow, and balancing issues arise. The basic problem is that your furnace fan will only come on when there is a call for space heat or cooling, whereas ventilation requirements occur year round (even during seasons when no heat or cooling is required). All solutions to this problem involve compromises, which is why GBA recommends that HRVs and ERVs be installed with dedicated ventilation ductwork.

  2. IRFL | | #2

    Hi Martin,

    The home is about 7500 sq. ft. located in Massachusetts. I was not involved in the design or energy consulting of this home. I was called in after to perform a infrared scan for insulation, air sealing and moisture concerns.
    I am not sure why they installed two ERV's, maybe because they hooked them up to the HVAC system?. I agree the HVAC contractor should have balanced the ventilation system. Apart from installing dampers in the ERV duct system I am not sure how to do that? I agree running the ERV supply into the return duct is part of the balance issue. However the fresh air supply was installed into the air handler return to prevent colder air from blowing directly into the room during winter season.

  3. davidmeiland | | #3

    I assume you took a baseline pressure before measuring the -5.5 pascal pressure created by the mechanical equipment. Did you check the pressure created by the air handler and each ERV independently? It's hard to imagine that the ERVs are creating much negative pressure, and I'm nore inclined to suspect the air handler and supply duct leakage to the outside. Perhaps duct testing is in order. You will have to somehow seal off the ERV duct connections, or at least the exterior terminations.

  4. GBA Editor
    Martin Holladay | | #4

    Flemming,
    Balancing instructions are provided by ERV and HRV manufacturers as part of the standard instuallation instructions.

    Basically, you adjust the airflows with dampers, and verify a balanced condition with a magnehelic pressure gauge.
    Here is an example of an HRV manufacturer's balancing instructions (these are Venmar instructions from http://www.venmar.ca/AxisDocument.aspx?id=494&langue=en&download=true ):

    7.1 WHAT YOU NEED TO BALANCE THE UNIT
    • A magnehelic gauge capable of measuring 0 to 0.5 inch of water (0 to 125 Pa) and 2 plastic tubes.
    • The balancing chart located on the unit door.

    7.2 PRELIMINARY STAGES TO BALANCE THE UNIT
    • Seal all the unit ductwork with tape.Close all windows and doors.
    • Turn off all exhaust devices such as range hood, dryer and bathroom fans.
    • Make sure the integrated balancing dampers are fully open.Turn the thumb screw (A) clockwise
    to manually open the dampers.Both are located on the Exhaust air to outside port and on Fresh air to building port.
    • Make sure all filters are clean (if it is not the first time you balance the unit).
    7.3 BALANCING PROCEDURE
    1. Set the unit to high speed.
    Make sure that the furnace/air handler blower is ON if the installation is in any way connected to the ductwork of the cold air return. If not, leave furnace/air handler blower OFF. If the outside temperature is below 0°C / 32°F, make sure the unit is not running in defrost while balancing.
    (By waiting 10 minutes after plugging the unit in, you are assured that the unit is not in a defrost cycle.)
    2. Place the magnehelic gauge on a level surface and adjust it to zero.
    3. Connect tubing from gauge to EXHAUST air flow pressure taps (see diagram beside).
    Be sure to connect the tubes to their appropriate high/low fittings.If the gauge drops below zero, reverse the tubing connections.
    NOTE: It is suggested to start with the exhaust air flow reading because the exhaust has typically more restriction than the fresh air, especially in cases of fully ducted installations or source point ventilation. Place the magnehelic gauge upright and level.Record equivalent AIR FLOW of the reading according to the balancing chart.
    4. Move tubing to FRESH air flow pressure taps (see diagram). Adjust the fresh air balancing damper until the fresh air flow is approximately the same as the EXHAUST air flow.If fresh air flow is less than exhaust air flow, then go back and adjust the exhaust balancing damper to equal the fresh air flow.
    5. Secure both dampers thumb screw in place with tape.
    6. Write the required air flow information on a label and stick it near the unit for future reference (date, maximum speed air flows, your name, phone number and business address).
    NOTE:The unit is considered balanced even if there is a difference of ±10 cfm (or ±5 l/s or 17 m3/h) between the two air flows.

    Exhaust air flow
    To avoid balancing, the difference between stale air ducts total length and fresh air ducts total length must not exceed 50 ft. However, even if the stale air ducts and fresh air ducts lengths are almost equal, your local building codes may require balancing the unit.
    If the unit does not need to be balanced, shut all the pressure taps (located on the unit door) with the small plastic plugs included in the hardware kit.

  5. MJDesigns | | #5

    Flemming,
    You asked if there were a unit available that automatically balanced the air flow and pressure ... this unit from UltimateAir does just that. In fact, they believe it's acceptable to share the forced air supply ducts within the existing HVAC system (not relying on the blower motor of the HVAC system but using their efficient brushless ERV motor) if there are dedicated exhausts from the bathrooms, laundry, etc.

    http://www.ultimateair.com/products/standard-features/

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