HRVs and make-up air

11 01 2011

Okay, we’re back…
Yes, we did have difficulties. The HVAC took a long time to complete, and momentum was lost…
However, it was regained, as following posts will show.
But before finally getting to the home stretch of this project, it is important to discuss the role of the Heat Recovery Ventilation units (HRVs). Each of the three apartments at Liane’s house received one as part of the HVAC upgrade. HRVs basically act as the “lungs” of the house. They are mechanical ventilation systems that bring in fresh air which has been pre-heated by heat captured from the stale, return air. The old air isn’t mixed with the new air–but its heat is. This is done by means of a “core”, which looks like an aluminum cube, through which many little air-passages flank each other. Heat gets transfered but the two different air-streams never actually mix.

Fantech HRV unit–how the core works

One of Liane's HRVs (from the outside)

A tightly retrofitted house needs air because the usual leaks and drafts that one doesn’t want are no longer there. Controlling ventilation mechanically and efficiently is one of the hallmarks of a Deep Energy Retrofit. The air Liane’s HRVs bring into her house is at about 90 cfm–just like a little breath, and heat energy is saved (some extra electric does get used by the fan).  The air is supplied to either end of each apartment, and is exhausted through the bathrooms–for a good mixing. Rigid ducts were used where possible for less friction, and programming of controls was kept simple to save on costs.

One HRV supply line
Another thing we had to do was to supply make-up air to the kitchens of the three apartments, so that the gas stoves would have plenty of air.  We also needed to vent the stoves to the outside, and make sure that the make-up air went on with the stove ventilation.  It was useful to have the new chase where the chimney had been, to install the make-up air lines behind the stoves.

Third floor chase where chimney had been

Rob from FAI installing the booster pump for the make-up air

The new chase is now conveniently behind the stoves, where the old chimney had been.

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