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.



1 10 2010

After much mulling over with our mechanical consultant, we decided it would be best to remove the forced hot air systems in Liane’s house, and go with an all hydronic system. The first thing the plumbers (FAI) needed to do was to remove the leaky oversized ducts, which also made it possible to walk around the basement without hitting one’s head. The sheetmetal was eventually picked up for recycling.  Below is the old 2nd floor return duct which had been located inside the 1st floor hallway at the back door.   No wonder the 2nd floor could never get proper air mixing and balancing.   The next thing was to decide what to do with 1 old hydronic boiler, 2 forced hot air furnaces that made a racket and blew dry hot air most unpleasantly–and 3 not-so-efficient domestic hot water heaters? Well, we gave them to the electrician (except for the ancient boiler). This way they could be repurposed for the electrician’s shop use, and Liane could go with a very efficient, quiet, hydronic, combined space heating and dhw system. The system we selected with the help of our mechanical consultant, was a Heat Transfer product called the Phoenix Evolution–a combined space heating, and domestic hot water–modulating, condensing unit. It is compact and very energy efficient, and can be easily integrated with solar hot water panels, which Liane would like to install in the next phase of this project, perhaps next year. There are some good tax credits for solar at this time.

Here is the Phoenix arriving.
Here it is out of it’s packaging–it’s pretty small, but pretty smart. One of those protruding boxes is a computer, and the other has rather elegant plumbing.

The Phoenix does weigh something though, and here it is being slid carefully through the basement bulkhead.

Rick, from Synergy was helping out with bringing the Phoenix to the basement, and he is at the base of the bulkhead steps in this image.

Once inside, it is positioned near a basement window through which it will vent and receive combustion air.

Now John and Bobby, the plumbers from FAI can start getting to work, to get all the domestic hot water switched over to the Phoenix.

Next, John from Boudreau Electric wires up what's necessary.

The supplier's representative and John look over the installation.