Air Source Heat Pump Freezing

matt_drummer

To get back to the subject of freezing and defrosting, they are an expensive inconvenience and alarming when first encountered.

But the performance of heat pumps need to be considered over the whole year, it's what counts.

Some days will appear to be horribly expensive, they are when looked at in isolation.

But a properly designed and installed heating system using a heat pump as the source of hot water is nothing to be scared of.

My efficiency on the worst days has never been below 300% including heating the DHW.

Today my heat pump is running at nearly 500% efficient consuming 900w of electricity.

It is running entirely from the sun at the moment so my electricity cost is 15p per kWh, what I have lost in export payment.

That means it is costing 13.5p an hour to run and 2.8p per kWh of heat produced. A gas boiler at 90% efficiency would need gas at 3.1p per kWh to be more cost efficient

Even on the standard electricity tariff the cost of heating today would still only be about 6p per kWh of heat.

I do realise that they are expensive to install, they can be tricky to set up and that not everybody has the resources available for solar panels and batteries.

But air source heat pumps do work, they work in our climate and in our houses and they are a viable heating source.

There will always be examples of poor installations and poor set ups but that is not the fault of the heat pump, just the people who install them.

They will all freeze up at times but the best way to mitigate the problem is to run the lowest flow temperature you can that delivers the heat the home needs.

JSHarris

Reed_Richards said:

QrizB said:

Reed_Richards said:

BobT36 said:

How is it for hot water? Do you need a "cylinder" setup? I presume they can't just heat "on demand" like a Combi? I've never had a cylinder since I was little, so always just been used to hot water (washing hands, pots, showers) on demand. 

I'm not trying to pre-empt Matt but all heat pumps systems need a hot water cylinder.

The alternative, if you don't have space for a HW tank, would be to fit an instantaneous electric hot water heater, working much like your combi boiler. Far more expensive to run but cheaper to install and can be tucked away somewhere, in a cupboard or under a sink.

Those instantaneous water heaters can draw quite a lot of power, particularly if you want a decent flow of hot water.  Heat pumps can also draw quite a lot of power when running at full tilt.  You might need to check that running both together couldn't exceed the capacity of your mains supply.

Very true for instant water heaters, they need to be at least 10kW to give the bare minimum as a hot water supply and even then the flow rate will be pretty low, much lower than for other forms of some other means of providing hot water, like a combi boiler, mains pressure hot water cylinder or thermal battery.  I ran a 10kW Stiebel Eltron instant water heater as a temporary hot water source (when building the house) and with an incoming cold water temperature of 8°C it delivered hot water at less than 5 litres/minute at 40°C, so pretty feeble for anything other than hand washing.  It noticeably dimmed the lights when it turned on, too, as it drew over 40 amps when running.

I don't think this is necessarily correct for heat pumps, though.  I have an ASHP that it rated to output 7kW maximum.  It slowly ramps up to draw about 1.5kW from the supply for the first few minutes after it first starts.  After about ten minutes the power it draws reduces gradually and settles to between 600W and 900W when it's running (depending on the heating load).  Admittedly my heat pump is relatively small at 7kW (although still much larger capacity than I need) but even one double the size is unlikely to draw more than 3kW to 4kW when starting and may well settle back to run at half that.  Not much different to an immersion heater, although it will be running a lot longer, perhaps.

There was a lot of rubbish in the media about heat pumps and electricity demand a few years ago, driven in part, I believe, but journalists who mistakenly assumed that heat pump output equated to their electricity consumption.  Perhaps understandable given the general lack of interest by many journalists in accuracy - a dramatic-sounding story is far more likely to earn them money, perhaps.  The reality is that a properly installed heat pump will output around three to three and half times more heat energy than the amount of electricity it consumes.  Over the past, very cold week (down between -4° and -8°C overnight here) our heat pump daily electricity consumption has been a bit higher than normal, averaging about 6.6kWh/day, or about 940W for the 7 hours each day it has been on.  That doesn't seem too bad to maintain a 1,400 square foot detached house at between 21°C and 22°C.

BellaBlondykeTheThird

I suspect the OP is long gone with the repeating posts seemingly sparring with each other over their setups and forgetting what this post is about.

However I will echo others in saying that a well setup weather compensation or knowing what the lowest flow temperature you can set for your property means the system should just chug along efficiently and constantly. I have not experienced any freezing of the outside unit.

matt_drummer

BellaBlondykeTheThird said:

I suspect the OP is long gone with the repeating posts seemingly sparring with each other over their setups and forgetting what this post is about.

And that is why they have a problem.

It is related to their issue. Their heat pump is not set up correctly and their radiators are probably far too small. All of this means that their heat pump freezes and needs to defrost frequently and they don't get enough heat in the house.

Refusing to listen to the reasons (not that I am saying they are) and dismissing examples of heat pumps that work well and thinking that it's not related are the problem.

The heat pump is just a machine that produces hot water, what you connect it to influences how it works.

If anybody just came on with no credibility and just explained what the problem was they wouldn't be believed.

Evidence of how to make it work and to show what is possible gives confidence in the replies and that their heat pump could work well if installed and setup correctly.

I'm no heating engineer and so I have no qualifications to offer advice. All I have is my experience with my heat pump.

Others do the same.

If you would prefer not to hear from people like us then we will just not post anymore.

If the OP needed and wanted professional advice and assistance then they should have gone to a professional rather than an internet forum frequented by amateurs.

If they were hoping that somebody here was going to tell them that all they needed to do to cure all of their issues was to change switch three to position two then they are going to be sorely disappointed.

JSHarris

I 100% agree with you, @matt_drummer , your experience mirrors my own with my heat pump.  I also am not a heating engineer, but my experience with my heat pump has taught me a lot, not least because it was, as supplied, set up very badly for use in the UK, let alone use in my specific installation.  Adjusting settings on my unit made a massive difference to performance and running cost.

JSHarris

Of direct relevance to the question by the OP of this thread is that, as supplied, my heat pump used to ice up.  Not in cold weather, as once the air temperature gets below freezing there's very little water vapour left in it to condense out, but in cool, damp, weather mostly.  The internal indication was the heat pump reverse cycling and pumping heat from the house to the heat pump to defrost the evaporator (which in defrost mode becomes the condenser).  Easy to spot as the flow temperature would take a nosedive.

It took some detective work to understand both why the heat pump was doing this and find which settings needed to be changed in order to stop it behaving like this.  I made lots of changes to the installer settings on my unit, the last one of which was turning off weather compensation.  As I only need a flow temperature of around 30°C weather compensation was both pointless and worse, it caused the heat pump to try and reach a higher flow temperature, which in turn caused a poorer COP.  This may not be a universal truth, but for me turning weather compensation off made a useful improvement.

Now that I've had several years experience of running the air source heat pump in a wide range of weather conditions I'm confident that I've got it set up to run about as well as it can.  It will still occasionally run a defrost cycle for a few minutes, but only in cool and wet weather.  I've never seen my heat pump ice up as shown by the photos earlier in this thread, so I would suggest that that unit either has a fault (too low a refrigerant level?) or is set up badly.

MultiFuelBurner

QrizB said:

"I am suggesting there should be a general ASHP discussion thread"

There is such a thread, over in Other Fuels. It is almost two hundred pages long but recently has been largely neglected.

I occasionally find myself referring back to my previous threads. If I think they might help people in the future I add a link to my signature block.

That's a good idea, sadly I don't think I've created any decent post worthy of that yet 😂😂

@curlylegend some pages back I put a link into carrier Heatpumps and since then another helpful post here said they were generally considered to be a good manufacturer.

I really would suggest you contact them direct and they could talk you through if what you have installed and if it is appropriately sized and your issues. They may indeed help you out of your predicament or help you find a local specialist.

Netexporter

Apologies if this has already been suggested but could the OPs problem be something as mundane as the condensate drain being blocked?

MultiFuelBurner

Netexporter said:

Apologies if this has already been suggested but could the OPs problem be something as mundane as the condensate drain being blocked?

https://www.carrier.com/residential/en/us/products/air-conditioners/air-conditioner-maintenance/clogged-ac-drain-line/

I don't think it specifically mentions freezing up but general maintenance on your heat pump if you fancy it is never a bad thing to make your heat pump run as efficiently as possible.

MultiFuelBurner

I know this is American but it suggest two things to check if your heat pump is freezing up and not defrosting

1) refrigerant level
2) defrost board

https://youtu.be/w4a75JACMyQ?si=mFqexS1ecpFKSDoE