MAILBOX: Goal: Low Energy Consumption


I could not agree more with Ken Last’s letter in HP173 about energy-wasting behemoth net-zero-energy homes. I would extend that to all net-zero-energy homes—regardless of size—that achieve that milestone by adding enough PV to atone for their energy-hog ways.

With PV costs to consumers continuing to decline, anybody with enough money can transform their existing home into a net-zero-energy one—without doing anything to reduce energy use. However, more than half the electricity consumed in a grid-tied home comes from the electric utility at night and on cloudy days, a substantial amount of which is typically fossil-fueled. This is the energy usage that needs to be reduced, at least until practical economic electricity storage is available.

So, rather than having net-zero-energy as the goal, we should have low energy consumption by the home as the goal. Homes should be rated accordingly, and the best way to rate homes is with a ”home heating and cooling index,” which objectively rates the structure’s energy requirements for maintaining a comfortable indoor temperature year-round. The house with the lower Btu of energy per square foot per heating-degree-day and per cooling-degree-day is the more energy-efficient home. An value of 4 or less would indicate an energy-efficient home.

Because the energy a home consumes over its lifetime is the single biggest amount of energy involved, the index is the most valuable energy measure of a home. My home’s value is 4. What’s yours?

Tom Wehner • Santa Fe, New Mexico

Comments (3)

Peter Gruendeman_2's picture

It is the unusual home (at least here in the La Crosse, WI area) that benefits more from renewables than from air sealing and adding insulation. Of the approximately 30 homes I have thermal imaged around here, exactly Zero had properly installed windows. Some were old; more were brand new. Thermal imaging showed substantial air leakage between the window frames and the rough openings of the structure. These gaps need to be foam sealed (window & door type Great Stuff or equivalent) so they are pressure-tight. Wadded up fiberglass insulation stuff into these gaps is not pressure-tight. I generally do Not encourage people to install new windows unless there is obvious damage to the sashes or frames that can not be sealed with 'V' seals or other techniques that allow the old windows to still be openable. Much more helpful than installing new windows may be to properly install the windows you already have. Do NOT assume that your new windows were properly installed. 0% of my admittedly small sample size were installed right.
Removing the window trim to check for proper sealing, or testing with incense on a windy day is easy to do. When I removed the trim from one of my windows, I could see right through the house. Sadly, this is not uncommon but it is easy for the ambitious DIY-er to fix. The cost is very low-- $2-4/ window and 1 to 3 hours per window, total time.
Pete Gruendeman's picture

FINALLY! This energy conundrum we find ourselves in makes me chortle. I live in Alberta, the Canadian version of Texas just smaller. We are in a battle with OPEC and of course the USA for energy to market.
That said, i've been involved with solar, including net zero and passive house programs for the past 5 years.
I get folks asking me about how to convert their existing stick built home to net zero (not passive as that is a new conversation).
They seem to feel that if they install a PV system (grid tied of course), they have done their part to working towards net zero.
Then they ask me why they are not reducing their consumption....

Well, the laundry list gets very big, very quickly in a conventional stick built home with minimum code construction.
I agree with Peter Gruendeman_2, I advise anyone to start first with the shell of the home. Insulate, insulate, seal and be sure to provide proper ventilation to the newly sealed up home.

Second, I advise them to upgrade all windows & doors to 3 pane, thermally broken, multi-point turn & tilt systems. I also advise them to change the size of ALL north facing windows to a specific size to reduce exposure and most of all, it helps to increase R values (as that is what most people seem to only understand, but it is much more than that as we know).

Then we highly recommend a blower door test, the house is now semi-sealed up, but the door test is the real eye opener (before and after). Then we take a look at the current HVAC system. This has EVERYTHING to do with an ability to get "off-grid" and most folks are not even aware of just how much power is consumed by the HVAC system alone and now the house is sealed up, with no way to exchange old, stale are for new heat exchanged air.

I then advise people to look at their appliances and upgrade to more than "energywise" appliances. This is a separate conversation as well, but is necessary to reduce their carbon footprint and lower consumption.

I then advise we monitor consumption habits for a month, so that at the end of that month, a review is necessary to determine habits of power use/consumption and determine who/what is the culprit of increased power use and see if that can be addressed/changed in any manner to reduce the load.

After that, a PV system is then discussed and matched to NEW load useage.
Far too many folks simply think a pv system will help (it pacifies them and they feel as tho they are doing their part, when in fact, it may actually make it worse. I say that as once people install a grid tied system, they seem to think that they are generating their own electricity, of which they are, so they start to use more, thinking that it's the PV system first and grid system 2nd. Only to find out in winter, the PV system is unable to meet demand and the grid system takes over and then the reality sets in.
The $32,000 they just spent on the under spec'd 5kWh PV system is not meeting demand and they want to know why.
The can of worms is now open.

There are now many "consultants" who will advise on a PV system, our local utility company also now "leases" a really small pv system (appro. 2.4 kWh), for around $300 per month added to your utility bill. It does not address ANY of the above items, just sells a system to the unsuspecting. Imagine, paying $300 + per month on top of already high utility costs!!!
(Prices are examples of the high cost of labour and PV system in Alberta as of 2016, and can be found cheaper to be sure, however if you are in business you will understand the metrics of costs. We know in the USA it will be cheaper).

Peter Gruendeman_2's picture

Hi: I ran the numbers for my house and also for the nine members of the sustainability discussion group I was a member of. The members brought their January and July natural gas bills, or their annual propane bills and square footage of their homes. I took the heating degree day info from The ten values for BTU/ HDD/ ft2 ranged from 2.4 to 10, with the two lowest having solar thermal heat and the highest two being typical 1960s 2x4 construction with the homes in good repair. These two homeowners were unaware that their heating bills were that far from typical. Both really wanted to put PV on their homes until I steered them towards insulation improvements as providing more benefit for less $.
That was because their homes were that bad. At some point (BTU/ HDD/ ft2 = 3- 4?), renewables are more cost effective for reducing energy use, especially on retrofits. Adding insulation beyond filling the existing wall cavities and insulating one's foundation can be expensive. No amount of insulation will provide domestic hot water.
Pete Gruendeman, La Crosse, Wisconsin

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