Comments on: Heat Pumps, Auxiliary Heat, and Resilience

By: Steve

Steve — Tue, 27 Jul 2021 22:13:43 +0000

My concern is the cost of making a 1961 house airtight vs having a second natural gas emergency heat source. I live in Wisconsin, near Milwaukee, and we get cold weather. I think the cost of converting to heat pumps and making the house airtight would be prohibitive. Escpecially since I’m retired on a fixed income and not a handyman.
When I lived in California my house had a Williams gravity wall furnace. No electricity required. I was thinking of having one installed in my basement so in case of a power outage I could keep my pipes from freezing and even live in the basement for a few days.

By: David Butler

David Butler — Wed, 14 Apr 2021 17:06:04 +0000

In reply to Bill Cowhig.

Bill wrote: “…just at the time (natural gas) has grown in importance, since gas lines are run underground

It’s true that natural gas service is generally more robust than the electric grid during wind or ice storms, but as we saw this year in Texas, gas distribution is by no means guaranteed. Although I don’t have natural gas service, I’m aware that gas distribution was interrupted in my region (SE Arizona) for multiple days during winter in recent years.

One advantage that heat pumps have over gas heat is that they can operate on a generator (you need a generator anyway to operate a gas furnace when the power is down). I used to live in Charlotte where ice storms were a common occurrence. I could easily keep my passive solar house comfy during an extended outage with a 6kW gasoline generator (http://veryuniquehome.com). Rather than dedicate specific circuits to the genset, I installed a (manual) transfer switch that back-fed power to the whole house. I just had to manage the largest loads when operating on generator power, e.g., disable heat pump when I needed to energize the water heater.

Today’s multi-stage or variable heat pumps could operate on a much smaller genset due to the ultra-low start-up current. Also, a diesel generator would be more convenient since diesel can be more readily stored on site.

Solar power with battery backup is becoming more feasible now that hybrid inverters are available that operate on- or off-grid. But this approach to resilience is still considerably more expensive than a generator backup system per kW capacity.

Lastly, for new construction, you can’t beat classic passive solar design in terms of cold weather resilience. Unfortunately, it’s fallen out of favor in recent years.

By: Lloyd Hamilton

Lloyd Hamilton — Wed, 14 Apr 2021 12:28:40 +0000

Why ignore ground source heat pumps? Not only can they operate well below zero, their efficiency and capacity hardly drops at all during cold snaps and they do not need supplemental heat if installed in a high performance building. If one is trying to achieve zero net energy then GSHPs are cheaper to install because they use less than 1/2 the electricity a quality ASHP uses in northern climates. They do not need supplemental heat in most cases. If one is trying to achieve zero net energy then they can be cheaper to install because of their significantly lower use of electricity.
They are also much easier to repair, even in really bad weather because they are entirely inside the house (other than the ground loop, which is under the ground.)

By: Ryan Shanahan

Ryan Shanahan — Tue, 13 Apr 2021 20:39:37 +0000

Building in resiliency and simultaneously going all electric is quite the challenge. Given the ridiculous cost of backup batteries that would only be useful to me in extreme cases (since we have no time of use electric charges and a 1:1 purchase power agreement with our electric utility for our solar PV that effectively allows me to use the grid as our battery) I’m holding out for the day when I can utilize the 40 kW battery under the hood of our new electric car to power my house in an outage. To me this seems a much more appropriate use of batteries, but I have to admit that draining the battery of our possible escape route in an emergency also presents a new challenge.

By: Bryan Uhler

Bryan Uhler — Tue, 13 Apr 2021 17:28:37 +0000

While it isn’t a popular thing in the minds of some, we install gas or propane fireplaces in our houses. Realistically, they rarely get used as we install VRFs standard in our homes, and we standard make our houses generator ready. However, I like the idea of a homeowner not having to one hundred percent rely on a generator or grid electric for those times of extreme weather conditions.

By: rjparker

rjparker — Tue, 13 Apr 2021 17:17:31 +0000

As one of the millions of Central Texans who spent a week iced in at home, a backup propane generator and lp furnace would have be a great addition to our 35 year old heat pump house. While not advertised, we do see ice and snow every few years but not for seven days at a time. In 2018 it was three days in our very hilly countryside. Many millions had no electricity or water for days on end. Most had rolling outages. While passive house construction would solve the thermal problem, what is the solution for the other 29 million Texans that don’t have that luxury? Certainly more secure powerplants and interconnected grids would be a start. Traditionally the solution was residential fireplaces, while theoretically inefficient, they did save the day for many this year.

By: Allison Bailes

Allison Bailes — Tue, 13 Apr 2021 17:16:54 +0000

In reply to Bill Cowhig. Bill, your building enclosure improvements can do the heavy lifting for your emergency heat planning. The auxiliary heat for an air source heat pump is used mainly for supplemented the compressor heat when it's really cold outdoors. When your heat pump fails, that auxiliary heat can become your emergency heat. I didn't mention it in the article, but another part of the solution for an all-electric home can be storage.

By: David Butler

David Butler — Tue, 13 Apr 2021 17:12:15 +0000

A system comprised of 2 or 3 (smaller) single-splits is not only more resilient (than a multi-split system), it’s more efficient and often costs less.

By: Bill Cowhig

Bill Cowhig — Tue, 13 Apr 2021 14:41:53 +0000

When electric power is down for a week, an increasingly probable scenario due to increasing intensity of storms caused by climate change, how can electricity be used as a “backup” in whatever form? You severed yourself from the natural gas line just at the time it has grown in importance, since gas lines are run underground. I am thinking about this because I am planning on installing a Bosch 18 .5 SEER heat pump package unit to replace our failed gas pack, and have decided not to buy it with an electric emergency heat strip, so have more than a little concern over cutting our gas line. We live in central North Carolina, and made it through the winter without our gas furnace using 4 1.5Kw space heaters. And that is without doing all the work I plan for sealing, insulating, etc.

By: Allison Bailes

Allison Bailes — Tue, 13 Apr 2021 14:17:28 +0000

In reply to Jamie. Jamie, air-sealing always gets good marks on "plays very well others." Yes, you get some air exchange when you open doors, but you've eliminated the "doors" that were open 24/7/365.