Real World Indoor Temperature & Relative Humidity Performance During Spring

Passive House/Passivhaus Real World Indoor Temperature & Relative Humidity Performance During Spring

As promised in an earlier article, I am providing some real-world indoor temperature performance in our Passive House during this Spring.

We have yet to install a computerized indoor temperature and relative humidity sensor system, so I am instead taking snapshot measurements manually with my pocket psychrometer.

This Spring continues to be on the cold side with temperature routinely reaching into the low to mid 30s in the evenings and the 40s during the day time.  Puxatony Phil was quite a bit off with his prognostication of an early Spring, this season (I understand Ohio was suing him for his error, by an over-zealous prosecutor), although their groundhog (Buckeye Chuck) also did not see his shadow on Feb 2nd.  Fortunately, the charges have since been dropped.

For the last three weeks we have turned off our mini splits completely and have relied solely on the solar heat gains from the sun as well as the internal heat gains of occupancy and appliance use.  While this Spring has been predominately cold, we had a couple of relatively toasty days back-to-back when interior cooling was desired.

Without any active heating or cooling, we are consuming an average of 20-22kWh per day.  We found we were consistently consuming 26.5kWh per day until we turned off the power to both of the Fujitsu mini-splits at the electric panel.  Even in their off position, each mini consumes about 2kWh day with parasitic power consumption.  In a conventional home with much higher energy consumption a mere 4kWh per day usage would likely go unnoticed, but at our low consumption levels that usage amounts to about 17% of our total consumption!  I will be posting a future article on our energy consumption profile as well.

Here are some detailed results (format is temperature in fahrenheit and relative humidity as a percentage):

Date: 04-21-13 at 13.23 (cold day)

Outside conditions: 46F with a low of 33F during the night.

Family Room: 71.4/48
Master Bedroom 1st Floor: 72.1/48
Master Bathroom 1st Floor: 73.5/46
Foyer: 72.6/45
Office: 73.5/46
Dining Room: 72.8/47
Kitchen: 72.1/47
Mud Room/Aviary: not recorded
Laundry Room: not recorded
2nd Story Bridge: 72.5/46
Master Bedroom 2nd Floor: 72.1/48
Master Bathroom 2nd Floor: 73.5/46
Exercise Room (door closed): 69.2/47
Front Bedroom 2nd Floor (door closed):77.7/40
Bathroom 2nd Floor (door closed): 70.1/54
Basement 65.4/51
Movie Theatre Room: not recorded
Mechanical Room: not recorded
Basement Bathroom: not recorded
Dog/Grooming Room: not recorded
Cat Room: not recorded

Note: With both the exercise and front bedrooms on 2nd floor, carpet installation makes air flow restricted.  Need to make adjustments to door heights to allow for better air flow circulation.

Date: 04-12-13 at 09.00 (after two showers and ERVs remaining on low setting)

Outside conditions: 48.3/75 (cold day)

Family Room: 71.2/50
Master Bedroom 1st Floor: 71.4/53
Master Bathroom 1st Floor: 71.7/51
Foyer: 71.7/53
Office: 71.6/51
Dining Room: 71.6/54
Kitchen: 71.7/51
Mud Room/Aviary: 71.4/53
Laundry Room: 71.4/53
2nd Story Bridge: 71.4/51
Master Bedroom 2nd Floor: 72.6/55
Master Bathroom 2nd Floor: 72.6/51
Exercise Room: 71.6/49
Front Bedroom 2nd Floor: 72.3/46
Bathroom 2nd Floor: 72.3/54
Basement 69.0/51
Movie Theatre Room: 68.1/53
Mechanical Room: 66.8/53
Basement Bathroom: 66.9/53
Dog/Grooming Room: 68.1/53
Cat Room: 68.7/50

Note: Stiebel Eltron heat pump hot water heater acts as an air conditioner during operation, hence the lower temperatures in the basement.

Date 04-09-13 at 17.26 (hot day)

Outside conditions: 79.8/29

Mud Room/Aviary: 73.7/41
Laundry Room: 73.9/39
Kitchen: 74.3/44
Dining: 74.4/43
Foyer: 74.5/43
Study: 75.3/42
Bridge 2nd Floor: 75.3/42
Bathroom 2nd Floor: 75.2/42
Front Bedroom 2nd Floor (closed): 77.0/44
Exercise Room 2nd Floor (closed): 74/40
Master Bedroom 2nd Floor: 74.8/44
Master Bathroom 2nd Floor: 75.9/43
Family Room: 75.2/not recorded
Master Bedroom 1st Floor: 74.6/43
Master Bathroom 1st Floor: 74.6/45
Basement: 68.7/50
Basement Bar Room: 68.7/49
Mechanical Room: 68.7/49
Movie Theatre Room: 69.2/49
Dog/Grooming Room (with 3 dogs): 69.2/49
Cat Room (with 6 cats): 69.6/51


ERVs were generally set at level 2.  We have since programmed the Paul ERV to operate at 98% capacity at level 3 (versus the default 80%), so that we can over ventilate with our earth air tubes to lower indoor temperatures during moderate to hot weather. The Comfoair 200 is now set to level 3 as well, although we have not programmed it to operate at a higher flow capacity as we did the Novus 300 (Paul).  When temperatures drop, we lower the air exchange rate so we do not "over cool."  If indoor temperature or relative humidity levels rise, we increase the air exchange rate with both ERVs to lower them.

We are seeing the interior temperatures typically range from 67F to 72F.  Relative humidities vary from the 40s to the mid 50s (at their highest after shower use, when ERV are set a level 1, their lowest rate).

The effects of solar heat gain is clearly seen with the south facing rooms that have their doors closed and circulation air flow restricted.

We are considering ways to internally distribute the warmer temperatures picked up by solar heat gains with the cooler basement air.    More tweaks are in order even though generally the heat variances that exist between the first and second floors are minimal.


  1. Very interesting stuff, Bob. Keep it coming! interesting to know that the phantom load on the mini splits is so high.

    We are finally at the permit stage. Haven't heard yet from the architect if the building department needs more info or not. Ours will be the first passive house in the township so we're keeping our fingers crossed that the head honcho has at least heard of passive house.

  2. So do you have an idea on why the phantom load is so high?

    I'm seeing the same thing on my prior model 9RLS2, it's using 80watts idle [+/-10watts] with the head unit on or off.

    Sounds like a serious flaw in SEER ratings if the unit can suck down this much juice not running.

    I asked a friend with a Sanyo A/C only heat pump - 2 of them, and they use 10watts total phantom. He mentioned there is a crankcase oil heater that could be drawing those watts which wouldn't be necessary during warm temps.

  3. I do not. Haven't specifically asked Fujitsu why and what could be done to reduce those loads. I was quite surprised to see this. Even the Grundfos has a phantom load that the panel consumes.


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