Part I: Importance of Maintenance and Upkeep for Maintaining Optimum Passive House Temperature Performance and Minimal Electricity Consumption

Maintaining Peak ERV Efficiencies

As I indicated in my previous post, December's electric bill was higher than we had expected.  This Winter is proving to be especially cold and outside conditions have frequently exceeded our heat-load design parameters.  We have a had a couple of days where our temperatures were below that of International Falls and more than a couple of days where we were below those of Nome, Alaska.  This morning it was -1F. 

We also running a number of computer systems here 24x7x365.  I recently got a Kill a Watt meter and have gone throughout the house identifying and eliminating unnecessary phantom loads from equipment left on that do not need to be.  We have moved some of our entertainment equipment off to a power switch and have turned them off and we are being mindful of turning off the two laser printers that we have in our home office. 

Beyond the higher than expected December electric bill, we had been finding that we were experiencing some room-to-room temperature variances that were greater than expected and we also began questioning the performance of our two mini splits.  Both units felt like they were working hard(er) but not really delivering the heat that we desired.  I was beginning to believe that perhaps we had been experiencing a coolant drop in our heat pumps.  Yes the COPs drop when temperatures get really low, but even at these super low evening temperatures, the Fujitsu RLS2s should have been producing a good amount of heat.  What I instead was finding that when they were running, the supply temperatures were only in the 90s not the 120s or 130s.  Clearly something was amiss and the temperatures in the house suffered as a consequence.

On January 4th at 07.35 we took spot readings throughout the home.

South Laundry Room: 65.3F/46%
South Bird Room (Door Closed): 63.8F/48%
Mud Room: 64.4F/48%
East Kitchen: 65.3F/47%
North Family Room: 66.3F/44%
West/North Master Bed 1st Floor: 66.3F/46%
Master Bath 1st Floor: 66.2F/47%
South Dining Room: 66.2F/43%
South Study: 66.2F/43%
Powder Room 1st Floor: 66.2F/42%
South Foyer: 66.5/43%
Bridge: 69.8F/39% 
West/North Master Bed 2nd Floor: 69.2F/40%
West/South Master Bath 2nd Floor: 65.4F/45%
North Facing Bedroom 2nd Floor: 64.2F/41%
South Facing Bedroom 2nd Floor: 64.5F/43%
Basement: 66.5F/43%
Media/Movie Theatre Room (Basement): 66.5F/43%
Mechanical Room (Door Closed with Stiebel Eltron DHWH): 66.2F/41F
Bar Room (Basement): 66.3F/42%
Dog/Cat/Pet Laundry/Grooming Room (Basement): 65.6F/42%

I first looked at both of our Zehnder ERVs and took temperature/humidity readings at each of the four ports of each.  This is what I found.

Zehnder Novus 300 (Paul)

Intake (EAT Supplied): 46.4F/38%
Exhaust: 51.2F/44%
Return: 66.7F/42%
Supply: 62.7F/41%

Zehnder Comfoair 200

Intake (EAT Supplied): 48.9F/35%
Exhaust: 52.8F/31%
Return: 67.2F/43%
Supply: 57.5F/30%

As you can see the 10 degree temperature delta between the supply and return temperatures of the Comfoair 200 was indicating something was awry and could be accounting for rooms of the house (supplied by it) that were noticeably "colder" than others, especially when their doors were closed.

The very high heat-exchange efficiencies of the Zehnders (92-93%) should be allowing for a greater amount of heat recovery (temperature) between the supply and return.  In the case of the C200 we were off six additional degrees than the Paul unit.

Examining the duct connections, I found some areas where leaks were occurring which could account for some pressure imbalances.  Using special duct tape, I sealed those areas.  Next I examined the filters of each unit.  Sure enough, they needed cleaning and with several of them, I outright replaced them with new ones.  I then took off of the covers of each ERV and removed the enthalpy units.  They were an absolute mess!

I used a vacuum cleaner and a brush to clean them off thoroughly.  I even sprayed a little bit of clorox and water blend onto the grills of each.  Fortunately both Zehnders are easy to disassemble and clean.

Once everything was back together and running I retook my measurements.

Zehnder Novus 300 (Paul)

Return: 67.6F/44%
Supply: 63.1F/45%
Exhaust: 51.2F/47%

Zehnder Comfoair 200

Return: 68.0F/43%
Supply: 63.6F/42%
Exhaust: 52.8F/53%

Clearly one can see that we got our expected efficiencies back, picking up more than six degrees on the supply side of the C200! 

Later in the day without any other changes we retook most of our readings through out the home:

At 13.35

East/North Facing Bedroom 2nd Floor (Door Open): 69.6F/41%
East/South Facing Bedroom 2nd Floor (Door Closed)  70.3F/38%
East/South Facing Bedroom 2nd Floor (Door Open): 71.7F/38%
Bridge (overlooking family room): 71.4F
Bridge (overlooking foyer): 73.1F
West/North Master Bedroom 2nd Floor: 71.2F/40%
West/South Master Bath 2nd Floor: 72.3F/40%
East "Shared" Bathroom: 71.0F/40%
South Dining Room: 71.2F/39%
South Study: 71.0F/39%
North Family Room: 71.0F/39%
West/North Master Bedroom 1st Floor: 69.4F/42%
Powder Room 1st Floor: 69.8F/43%

Beyond the heat gains of the morning and early afternoon sun, the temperature variances dropped from 5.7F pre-cleaning to 2.7F post-cleaning.  Clearly not only did we improve our heat recovery performance from the ERVs (ie; retaining of heat during fresh/stale air exchange) we also reduced room-to-room temperature variances.

It is easy to forget those trusty ERVs since they quietly just do their job, but our experiences absolutely underscore the importance of performing routine checks and cleaning of them.

Next, we looked at our point-source ductless mini splits...