I have a 17kw Grant Aerona heat pump to heat a large 4 bed detached property and I have to say the installation has left me wishing I never embarked on the heat pump journey. I went through Green Match who put me in touch with a couple of installers of which I selected the one that said I would get a Grant manufacturers MCS install - this was the primary reason I went ahead with the install. As it turns out the person I spoke with was really just a middle man/sales person who seemed knowledgeable about heat pumps and even said at one point he was involved in setting up the MCS scheme himself which gave me some confidence that they would so a good job. The work was actually done by an independent installer (ex Grant engineer) who started the install and then half way through went on holiday leaving us without a working system requiring us to resort to using the immersion heater for hot water. Thankfully it was summer and we didn't need the heating. I can live with that if we were to get an install that worked. He completed the install and the system didn't warm any of new radiators they was cold and at best tepid. We also had a number of radiators oversized in the rooms based on the heat loss calcs but most didn't even come to temperature. I said the system can't be commissioned in the state it was left as it was just not working as per the design. I had a new born on the way and said this would never work in the winter. They made all sorts of excuses saying it's a piping issue and nothing to do with the install and trying to absolve themselves of any responsibility. They they went on to say it because we had a one pipe system which was total rubbish as it turns out after speaking with other plumbers.
In the end they would not give me the MCS certificate until I made the final payment and was left with no option to pay given new born was due. MCS were pretty much useless too and I really don't understand why they exist as they do not protect the consumer at all.
In the end I got another heat engineer in and he suggested putting in a circulating pump funnily in the same location as the one they took out because the heat pump circulating pump should have been powerful enough. This helped distribute the heat a little better although not to the levels expected.
In short, 3 years on I would say the system isn't performing and my bills have increased significantly as opposed to being cheaper as I told when all the calculations were performed. About a month or 2 after the install the compressor failed and the whole unit had to be replaced and I've had several blockage faults which shuts the unit down. Grant have been in a couple of times and they have told me the flow rates should be a lot higher than they in my system - 35 litres which I thought seemed high given my incoming flow rate from the mains is only 23lpm. I looked at the documentation and for the heat pump I have it mentions a minimum of 15lpm. Wondering if anyone else has their flow rates for when the heating is on and when the hot water is on?
I also installed the metering and monitoring option and can see that my efficiency looks to be 2.4 at the moment for December so far which is far lower than what Grant advertises. The highest I had is 3.26 in Aug when I wouldn't have been using the heating at all and only warming the hot water.
One of the things I'm now considering is putting under floor heating to remove any possibility of piping issue although I'm sure this will be pretty expensive.
I would love to hear from anyone else suffered similar issues and what they have done to resolve.
What I've learnt is to use established companies showing a good track record of designing a system properly and good after care as when things go wrong because they will inevitably.
Addendum to my previous post. Also I wanted to ask if anyone else sees the sort of consumption pattern in the picture attached where the heat pump comes on and then shuts down and then starts up again - I think it's called cycling.
Addendum to my previous post. Also I wanted to ask if anyone else sees the sort of consumption pattern in the picture attached where the heat pump comes on and then shuts down and then starts up again - I think it's called cycling.
Looking at the graph, what you refer to as cycling could possibly be defrosting.
What is the calculated heat loss for your Home? Do you know if your system is operating in weather compensation mode? What indoor temperatures are you trying to achieve? Are you using any thermostats for control? What is the size of your home?
Ensure that any TRV's are fully open, except those used in bedrooms where lower temperatures may be preferred. Check that all radiators are being adequately heated.
It’s a grant, it will be badly installed, in an inefficient manner. The Chofu unit that Grant re-badge is decent and is made in Japan, Grant just choose to install it like a boiler.
You need to get it re-plumbed, re-wired, and your flow temperatures turned down.
Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.
My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.
@soniks, so sorry to read this. All ASHPs in the UK at the moment will be routinely cycling into defrost. The compressor switches off and the system reverses function for a few minutes. When this happens heat from your house piping circuit is used to defrost the coil. It's not included in any manufacturer's SCOP or COP values, but at outdoor temperatures below 3 or 4degC ASHP coils start to build up ice. In very damp and cold weather, freezing fog for example, it can build up very quickly and the unit will be defrosting more often.
You'll notice that the water temperatures to and from your ASHP cools during defrost, as heat is lost through the house radiators and into the ASHP for defrosting. The ASHP has to work quite hard to warm the circulating water back up after defrost, so it's consuming quite a bit more electricity in the current weather. We're all seeing that right now!
The higher your set flow temperature, the harder job the ASHP will have to get up to temperature. Quite a few owners are finding their units are simply not reaching design flow temperature in the current weather. That doesn't necessarily mean their ASHPs are undersized, but if the unit is spending, say 25% of each hour in defrost or rewarming up after defrost, a 10kW unit is currently a 7.5kW unit. That's why lower flow temperatures can help because the ASHP doesn't have to work quite to hard to get back up to temperature.
The Grant 'default manufacturer's' install plans are not that clever. I have a 10kW Grant Aerona unit 'factory fitted' with pre-plumb cylinder, low loss header, secondary pump, conventional Stelrad K2 and K3 rads, etc. I've been doing a lot a tweaking of controls to get it as efficient as it can be in the current configuration. Most important is to have appropriate flow rates on the primary and secondary circulating pumps and to make sure they are balanced and comparable. My system is doing OK, but it's not exactly top tier performance. The Grant internal circulating pump is settable at one of 3 speeds. Even on the minimum speed my ASHP unit pump is more than capable of delivering the required flow through 28mm pipework to and from the low loss header.
The 17kW Grant unit has a specified rated flow at 55degC water temperature of 28 l/m, and at 35degC it's 51 l/m. By interpolation: your primary flow through the ASHP for 50degC water temperature should be sitting at 28+20% = 34l/m. So Grant's recommendation of 35l/min seems right.
Your secondary flow should match this with all the radiator valves open. This is especially important if they have installed a low loss header. Whether the secondary piping circuit (from the header to your radiators and back) can handle that flow I don't know. Your secondary pipework flow and return should be minimum 22mm pipe, and connections to rads 15mm. If it is, you should be able to get adequate flow and return and heat round the heating circuit unless there is some design or balance issue, a blockage or another problem.
For 17kW nameplate duty, at 34l/m flow, the ASHP water inlet and outlet delta T will be ((34/60)x4.2)/17 = 7.1degK. So if your supply water is 50degC, the return should be about 43degC. Grant's default delta T setting on the Aerona range is 8degC. If the difference in supply and return temperature on the secondary side is much more than 8degK the ASHP will struggle. Can you check what temperature difference you hve between flow and return? If it's over 10degK the ASHP will struggle, it should be closer to 5degK.
At 15l/m and 8degK delta T, your ASHP is only able to provide: (15/60)x4.2x8 = 8.4kW. Even at the maximum 10degK delta T Grant controller setting the 17kW unit will only kick out 10.5kW with that low flow. (The 15l/m minimum flow rate in the Grant literature is not the same as the proper design flow rate required. The 15l/m minimum is not high enough to get 17kW out of your ASHP.)
@hughf do you know anyone knowledgeable who could do this and would it invalidate any Grant warranty? I think you are right though grant just treat it as a boiler and the controls outside decide when it comes on and off. There is a passiv metering + monitoring installed which also controls when the heat pump comes on.
I don't think the unit is undersized if anything we went for something slightly bigger than what the heat loss for indicating as we were looking to extend the kitchen at some point.
How do I check what my delta T setting is on the Grant HP?
There is a 28mm pipe from the heat pump to a buffer tank and then to the main cyclinder.
There is no low loss header and not sure what it's purpose is. Could you help explain?
To get the higher flow rates do I need to change all of the piping and would it be best now to go for UFH?
See the graph below for usage in Oct when the unit shouldn't really be defrosting given outdoor temperatures are 7c+. It's not clear to me why it would come on for a very period and then switch off.
That doesn't necessarily mean their ASHPs are undersized, but if the unit is spending, say 25% of each hour in defrost or rewarming up after defrost, a 10kW unit is currently a 7.5kW unit.
Is this correct, I wonder? I'm getting at the old energy vs power thing again. Isn't the (max available) power (in kW or could for example if it was a car be HP) constant, but if the unit only runs for 75% of the time, then it uses/provides 75% less energy than it would if it ran 100% of the time (in car terms, if you only drive for 45 mins (still at top speed) out of every year, you use 25% less fuel and cover 25% less distance than if you drive for 60 mins of every hour). In the above example, the 10kW heat pump runs at 10kW for 45 mins and so uses/delivers 7.5kWh of heat/energy during that hour. The (potential) power remains the same, it just delivers less heat because it is slacking for 15 mins of the hour. I'm asking because I get so easily confused about all this, and suspect others do as well, and some definitive answers might help.
Midea 14kW (for now...) ASHP heating both building and DHW
@soniks if not all your rads are heating up you have a balance issue. You need to balance your radiators before you do anything else as it may be the reason you aren't getting a warm house.
Do you know how to balance them?
12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE
@cathoderay you're right, and my explanation is a bit confusing. I've seen my Grant ASHP spend a lot to time in defrost recently and it does tend to mean the average water supply temperature over an hour is less than the weather compensation demand temperature. It doesn't overshoot the supply temperature to compensate for the time it's below target during defrost and for the 5-10 minutes after as it warms back up. There's no trending to factor in defrost and compensate for lost energy delivered when in defrost. If an ASHP was only 'just' sized large enough, it may be found wanting when defrosting routinely in very cold weather.
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