We’re getting into commissioning residential heat recovery ventilation systems (balance* and optimize) and so recently invested in a Dutch-made balometer that is really accurate* for measuring low air flows. What was once done crudely with a Pitot tube and unglamorously with a garbage bag “should” now be able to be done quickly, simply and repeatably with more accuracy – perhaps too much – which may be part of the problem.

Generally, the procedure goes like this:

1- balance the adjustable dampers (if present) with the system at max speed
2- adjust flow down to Total Ventilation Capacity and label, then tweak dampers room by room to set flows as per mechanical design,
3- measure door undercuts and issue balancing report!
4- Go home for more rum and eggnog before it expires.

However, we’re having the Dickens of a time with one particular ERV. We use the balometer outside (sheltered and calm days, get a tight fit, do 3 readings in a row) to measure flows at the intake and exhaust, we can match those up to within 10% of each other (the criteria according to HRAI for a balanced system). But when we measure all supply and return grills indoors, the numbers don’t add up by a very large number.

This should be a simple reconciliation of flows on both return and supply sides. We can get the system balanced outside but flows inside are heavily lopsided or we can adjust the indoor supply return grill flows till balanced but then the readings outside are waaay off.

For example, we adjust indoor supply/return air flows to the designed rates (eg indoors we read 131cfm fresh supply and 102 return) but when we measure outdoors, we get 161 cfm stale exhaust and 90.3 cfm fresh air intake with a difference of 70cfm between intake and exhaust. For the record, the duct work in this house was meticulously air sealed.

There are two variables we haven’t accounted for yet.
1. How much air flow the ERV has by-passing though the media filter? 10% plus?
2. The ERV is “Self-balancing” and has a logic circuit in it that automatically adjusts air flows to “Balance” the ERV which might be unwittingly working against us…

As per usual, most installed HRVs and ERVs don’t lend themselves well to Pitot or flow collar insertion due to physical constraints. If you have any insights, I’d be much obliged!

*Balance: Flows into and out of home withing 10% of each other so as to not pressurize or depressurize.
Optimize: Set maximum speed on adjustable models and adjust flows room by room as per intended design by tweaking dampers.
*Nearly caused an international scene by calling the manufacturer’s claimed accuracy into question…it is pressure compensated and shouldn’t induce flow restrictions…. or so I imagine…