Comments on: My Undersized Heat Pump in an Arctic Blast

By: Norman Bunn

Norman Bunn — Sat, 04 Mar 2023 11:40:19 +0000

In reply to Bruce Murdoch. Even though we live in the Sunny South (Greenville, SC), we elected to put insulation at our slab perimeter and two feet into the slab from the edge. This has made our basement very comfortable, too, while providing a thermal store under the slab which limits large temp swings.

By: Bruce Murdoch

Bruce Murdoch — Fri, 03 Mar 2023 14:14:41 +0000

In reply to Galen. Yes, it is. We built the home with SIPs and in order for the basement walls to withstand the pressure of backfill, we needed a 9 1/2" thick wall, which happens to be R-40. We aren't required to put insulation under the slab here either unless the slab is hydronically heated but I can confirm it makes the lower level so much more comfortable!

By: Galen

Galen — Fri, 03 Mar 2023 12:30:57 +0000

In reply to Bruce Murdoch. That's some heavy basement insulation. Here in Maryland, code is no insulation under the slab if the slab is below frost (30") and R-11 for basement walls.

By: Bruce Murdoch

Bruce Murdoch — Thu, 02 Mar 2023 23:30:54 +0000

Check out my heat pump experience at -30F!
https://mindmuser.wordpress.com/2022/12/29/the-heat-pump-torture-test/?fbclid=IwAR2Z1TOQaNsyy1TN2uYoXdEapINmFbIKdMX9efXcA0OAQYhNc99T3gdVyus

By: Wayne Appleyard

Wayne Appleyard — Sun, 26 Feb 2023 15:06:32 +0000

If it an existing home with a year or two of energy bills those can be used to size a ASHP system(see size an HVAC system in 15 minutes on the web). You can add a resistance backup to give additional assurance it the system will do the job. On a new house, code requires a blower door test and a manual J in most cases although not all munis require it.
I have looked at the specs on the Mitsubishi that I have and with the variable refrigerant flow systems there is not much of a difference between minimum and maximum flow COPs at the temperatures they list so “undersizing” probably doesn’t effect efficiency and so I would just right size it.

By: John

John — Sat, 25 Feb 2023 18:28:56 +0000

Allison,
I read your blogs occasionally and know how you feel about blower-door tests. In the last 4 years I’ve been involved in purchasing high efficiency ACs and heat pumps for myself and family members. When I bring up the question of a blower door test I’m always told that that is old school and that their method of determining heating or cooling requirements gives the same results. I don’t believe that, but in my most recent experience, in small town Minnesota, there was no one in small town, or probably within 100 miles or more that would do a blower door test. The other problem is that if you want a particular brand, there might be only one authorize dealer for that brand within 50 miles and the one 50 miles away won’t travel 50 miles to do an install. In other words, you run out of options. The only answer to this dilemma seems to do the blower door test myself which I have not attempted yet. This was with a GreenSpeed system for a fairly large home. What’s your advice? Thanks.

By: Dana Fischer

Dana Fischer — Fri, 17 Feb 2023 15:42:46 +0000

In reply to Jim Matthews. It is pretty amazing. Can't post a picture here, but in January 2022 there was a stretch of weather in the single digits. On one of the coldest mornings January 11, 2022, I took a series of snapshots to show performance. 2F ambient outside (windchill -15F), the combined consumption of the qty (2) 1-ton FS12 systems was less than 3,100 watts at any given time. Inside house temp steady at 69F. I pointed a thermal sensor tool at the coil and read a temperature of 152.7F! I am sure the flowing air temperature out of the indoor unit was lower than that, but its pretty incredible what the hyper-heat systems can do.

By: Jim Matthews

Jim Matthews — Thu, 16 Feb 2023 23:54:27 +0000

In reply to Dana Fischer.

It’s hard to imagine a 125°F delta (-19°F –> 106°F) without resistance heating…

By: Dana Fischer

Dana Fischer — Thu, 16 Feb 2023 22:59:06 +0000

In reply to Kevin Cafferata. My experience is that they top out between 1,600 to 1,900 watts per ton in extreme conditions depending on the individual system and whether it is a ductless systems or has an air handler attached to the heat pump. I try to imagine that there could be a cycle in which they exceed the level that occurs when it is flat out and super cold, but I have not seen it in years of observing my consumption data.

By: Dana Fischer

Dana Fischer — Thu, 16 Feb 2023 22:52:53 +0000

In reply to Craig Long.

https://www.bostonglobe.com/2023/02/08/science/heat-pumps-had-their-first-major-test-last-weekend-heres-how-it-went/

https://www.bangordailynews.com/2023/02/14/business/heat-pumps-cold-weather/

“We have 1,500 heat pumps in the field, and we did not get a single call of a heat pump shutting off during this event,” said heat pump installer Josh Oxley, of SolarLogix in Belfast.”

“At my personal residence, I measured 106 degrees coming out of our heat pump when it was negative 19 Fahrenheit outside,” he said.

“It was a great test case, and they came through with flying colors,” said Michael Stoddard of Efficiency Maine.

“In certain homes where we’ve been watching very closely the effects of switching the entire home to heat pumps and removing the old central heating system, we checked in with each of those homeowners individually to see how it was going,” Stoddard said. “And they all reported that the heat pumps continued to work, and kept them comfortable in the home.”