Passive House Electricity Consumption: Reducing Electric Use

Current Electric Consumption

I am pleased to report that I have solved some of the issues that I have been experiencing of late during this especially cold winter season. 

In a previous article, I had indicated that I had received a higher than expected electric bill for the month of December.  As a result of this, I began to investigate where and what I needed to address to bring future bills more into line with what I was expecting.

To summarize, I undertook several corrective actions:

1) Cleaned both Zehnder ERVs to return their efficiencies in heat exchange to specified levels.  By cleaning thoroughly cleaning the enthalpy unit and the filters the temperature deltas between the supply and return were significantly improved.

2) Cleaned both mini-splits' filters and condenser units--that were absolutely cruddy--with a vacuum cleaner, toothbrush, and some water misting.

Both of these steps made substantial improvements to performance and in the case of the mini-splits the high level of work they had to do (energy consumed) to do very little was rectified.  They are now running using significantly less energy on average, producing better air flows, and are providing more consistent temperature performance at a higher COP.

These experiences have taught me that it is extremely important to perform routine checks and cleaning (when merited) to ensure tip-top performance .

Also in the case of the mini-splits, I experienced on one occasion a loss of some coolant early on.  Speaking with someone who installs these, I learned that this occurrence isn't entirely uncommon.  Furthermore, the mini-split in the family room (providing heat to the majority of the house--1st and 2nd floors) needs a replacement fan blade.  It is partially broken which is probably hurting heating and cooling efficiency somewhat.

Both of these remaining issues will be resolved when my HVAC contractor comes out to service them.  I would suggest that owners of minisplits routinely have their units checked.  I understand that the fan blades can often pick-up "crud" from accumulated dust and debris coupled with some moisture.  If the condenser, blades, and/or the condensate lines get gunky or clogged things can go sideways.  Take my advise and have them checked routinely (perhaps as frequently as twice a year).

Our eMonitor (now called SiteSage) system is continuing to prove its worth to me.  Using it, I have been able to confirm some of the problems mentioned above by their impact upon energy consumption.

I have since unplugged a wine cooler because it was a electricity hog, consuming about $24 per month alone in electric, placed some electronics on separate power switches, and identified three appliances consuming relatively high levels of phantom power--both Fujitsu mini splits and the Grundfos well-pump.  Between them they are consuming about 350 watts of electric continuously.  I will be looking at inserting a water pressure switch to cut-off electric to the pump controller when not in use and am considering manual toggle switches of some sort to cut the power to both minis when they won't be needed.

The minimum draws I have been seeing or about 620 watts.  Losing another 330 would get me below 300 watts nominal draw for the whole house--amounting to about a 50% reduction over current levels.  That amounts to up to another $20-$40 month of reduction in electric costs, potentially.

I can't stress enough how important it is to research the phantom loads of any electronics that you incorporate into your project.  While the Grundfos well-pump is certainly efficient when it runs, the overall efficiency is reduced because of such high levels of standby power consumption.  Speaking to Grundfos technicians, they themselves were not entirely knowledgeable of this fact and as such have taken my feedback to hopefully affect some changes.  In the meantime, I am on my own to come up with a solution.  The newer Fujitsu RLS2hs I understand have even a higher level of standby power consumption than our RLS2 models.  I am pleased to report that our Miele kitchen appliances are good stewards as is the Stiebel Eltron Accelera heat-pump hot water heater.  The Zehnder ERVs are also incredibly small consumers of electricity when running.

The next area of tweaking has positively affected the temperature performance and overall comfort levels in the home.  I will be covering this in my next article.