this post was submitted on 01 Nov 2023
533 points (98.0% liked)
Technology
59605 readers
3436 users here now
This is a most excellent place for technology news and articles.
Our Rules
- Follow the lemmy.world rules.
- Only tech related content.
- Be excellent to each another!
- Mod approved content bots can post up to 10 articles per day.
- Threads asking for personal tech support may be deleted.
- Politics threads may be removed.
- No memes allowed as posts, OK to post as comments.
- Only approved bots from the list below, to ask if your bot can be added please contact us.
- Check for duplicates before posting, duplicates may be removed
Approved Bots
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
I want to understand what happens when it's too cold out. And just running in pure air sourced HP mode, without supplemental heat.
Does it keep running at 100% but produces no heat? Limited heat? Does the house get colder and colder until everyone turns into a popsicle?
Or does it only heat the house to 18c instead of 20c?
In a climate where the low is -10c, how well does it work?
A heat pump will always generate a small amount of heat just from the compressor running, but most of the time that's a lot less energy than is being moved. As the outdoor temperature drops the delta between input and output air temp will decrease until the difference is entirely from generated heat in the compressor. Most designs would turn on extra resistive heating once the output temperature drops below your set target though. Modern designs are capable of moving a reasonable amount of heat even down to at least -25°C / -13°F now though.
It gets less effective, down to running at 100% and not moving heat. Heat pumps work by expanding a gas, which cools it. Since it's cold, the "heat" outside was the gas. Then the gas is taken inside and compressed, the gas heats up from the compression (since all the energy is squeezed into a smaller space, effectively speaking). Now that heat can be transferred to the colder air inside. So long as the expanded gas turns colder than the outside, it can absorb heat.
From a Google, common ones can go as low as - 25C, which means they are able to cool a gas to lower temps than that when expanded. There is still heat to get, even in -25C.
I have an air sourced heat pump and it gets to -35C for a few weeks at time here. When it's that cold it does produce heat but your breath is hotter. There's no point in running it as it just doesn't make any kind of useful heat. Below -10C the amount of heat it produces noticeably tapers off.
One thing that happens is that the defrost cycle takes a longer time, so it spends less time heating the building
I can only talk for myself but I have a Nibe pump here in Sweden with air source outside pump and water heating system to radiators on the inside. Even down to -30° with really shitty windows it was enough heat for me to be comfortable. Though it did indeed use the supplementary resistive heating a bit it was still able to give me about a 200% efficiency during that period. Give a typical winter (usually around -5-10C but, as said can go down to -20C or -30C for a week or so) it still runs an average of about 300-400% efficiency.
You either buy some portable electric heaters for those 2-3 weeks when it's necessary, or you get a heat pump that has resistive heating as a backup.