Balancing the ERV

The ERV (Venmar X24ERVE) has been installed for some time now.   It was installed in February to help with some of the moisture load associated with the drywall and plaster.   Three dehumidifiers weren't able to keep up with the moisture load so Adam (Hot Water and Fresh Air Systems) installed the ERV and we turned it on to help with the drying process.  Initially the system ran unbalanced but with the house under some depressurization so we both agreed that it was fine given that it was heating season.

Just before we moved in, we balanced the ERV.  The balancing the procedure for the X24ERV is fairly simple and all electronic.  The procedure is carried out using the x24 wall control.  First, the tubes of the differential manometer are connected to the ERV pressure ports.  The manometer provides a differential pressure reading in inches H2O.  The CFM is then determined from a data table included with the machine which represents stale air fan curve.  You can then adjust the fan speed to provide the air flow necessary.  Once this result is acceptable,  the manometer is connected to the fresh air flow pressure ports.  The CFM is then determined for the fresh air intake and the fan speed is changed to provide a pressure that corresponds to the same CFM as for the stale air.  At this point, you set the continuous ventilation as a fraction of the fan speed of the turbo mode.

This is just a  starting point.  Air flow then has to be measured at each diffuser in the system and matched to the mechanical plans.  Once the diffusers are modified, it changes the static pressure of the whole duct system and the ERV becomes unbalanced.  Each time modifications are made, the system has to be re-balanced.  It is an iterative procedure and it does take some time and patience to achieve balance and the correct air flow.

The system is currently running but there have been some problems.  The first indication of a problem was a problem the wood stove but it took some time to figure out what was happening.  On windy days the stove operated fine.  On calm days I noticed that the some smoke from the wood stove leaked out from the stove pipe connections inside the house.  Initially I attributed it to the chimney being cold.  But it happened again on another warmer day.  It was quite scary initially and we solved the problem by opening the windows.  After a few minutes it stopped.   We finally linked it to the ERV being unbalanced at the continuous operating mode.  When measured on turbo, the readings were fine.  On continuous mode it was out of balance even though we had balanced according tot the manufactures instructions.  Balancing the system so the fresh supply was 2-3 CFM more than the stale return fixed the problem.   The ERV balance is state is still better than 5%.  At some point I may explore other options for ensuring that It seems that air tight houses really amplify issues with draft.  Given that the stove pipe is not air tight, its not surprising.  Air will follow the path of least resistance into the house and the stove pipe is one of those routes.  If the ERV is unbalanced and pulling air at a rate greater than the natural draft of the chimney, smoke will spill into the space.  Now that I have seen what can happen with an unbalanced ERV, I will be more cognizant of the balancing issue.  Keeping filters clean will be important in order to maintain balancing.

The system is now working great.  I am pleased with my choice.  Choosing an ERV has worked out well during the heating season.  Relative humidity has been around 50% and nobody has been complaining about dry eyes, noses or dry itchy skin.  As suspected, with triple glazed windows, there have been no issues with condensation.

Photo 1. Testo wireless manometer 

Photo 2. Wireless manometer connected to the pressure ports for the stale air

Photo 3.  iPhone readout of the Testo manometer.  The x24 wall control is used to do the balancing while the manometer provides differential pressure readout.


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