Posted by: @bn06amp

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Hello, I'm new to the forum and also new to heat pumps as well, so please do forgive me if some of my knowledge isn't quite up to scratch. I appreciate there is a similar topic on here but I didn't want to distract from the great advice that Sonik is being given on that thread.

We had a Grant heat pump installed in Oct this year, our house is approx 250sqm and is underfloor heating throughout (upstairs and downstairs).

I accept that I'd (up until yesterday) had the ASHP set up completely wrong. Every single room in the house was zoned, with some zones completely off and other completely open. After reading useful forums, I've now completely removed all of the actuators from the manifolds and turned the central thermostat up to 30. Prior to doing this we were finding that the house was getting nowhere near to temperature and our overall consumption per day was 120 - 130 KWH, which is quite simply just not affordable, given the house was not heating up (it was really cold) and the system was still draining so much consumption, yesterday we simply just turned it off till we could work out the problem.

So last night we made the changes and turned everything back on, thermostat turned up to the max, house was still pretty cold this morning, but has now, very slowly started to heat up and is definitely going in the right direction. Everywhere seems to be heating pretty evenly (even the areas where we'd anticipate a high heat loss) with the exception of my daughters bedroom, which is still cold and I really don't know why.

Our heating curve is set to 50 degrees at 0 external temperature.

I used the advice on the other thread to look at flow, return and consumption

Flow - 45

Return - 42

Power 4600 - 4700

So with the above in mind, I had a few questions which I was hoping to get some advice on:

 - Given the pump is running the flow at 45 and the house is definitely heating up, should I adjust the curve down slightly - given the still pretty high consumption I'm wondering if this is because the pump is trying to reach a temperature of 50 which is just not realistic (and a flow of 45 seems to be heating the house up ok).

 - I was also advised that having a higher flow could be causing the heat pump to go into the defrost cycle more often, and turning the flow down slightly could reduce the amount of time the unit goes into defrost and draws heat from the system? Is this something people would advice.

 - Given the heat pump had been off, I appreciate it will now take some time to get the house to an even temperature, once this is achieved and I'm happy with the ambient temperature, would you expect the running costs to drop (as again running at 100kw a day just isn't rally sustainable!)

 - Any ideas why there is one room not heating up? Given the actuators have been removed, the valves to this room are fully open!

 - Our installer has offered to come connect the immersion up to the Pump. We use Octopus intelligent so we get a cheap overnight rate of 7.5p, would it be adviseable to have the immersion connected up and run this a couple hours overnight?

Any help and advice really would be hugely appreciated.

Ash

Hi Ash, welcome to the forum.

You should find that the energy consumption will start to reduce as your home gets up to temperature.

What model is your heat pump and do you know the calculated heat loss for your home? How many water pumps are installed and do you have a buffer tank or low loss header fitted?

Is your system operating in weather compensation mode?

With UFH you should not require a LWT of even 45C, since it will probably be mixed down to a lower temperature for the UFH.

With regard to the cold bedroom, it may be possible that the relevant flow valve at the UFH manifold requires adjustment. Posts some photo's if you can.

@derek-m Thanks Derek for the welcome! I'll do my best to answer the questions, but I'll give a bit more background info first as this might be useful!

The house has 4 UFH manifolds

 - Downstairs

 - Upstairs (main)

 - Room above garage (upstairs)

 - Extension added after the house was built

In terms of pumps, there is a pump that runs from the ASHP (I think) and then the UFH control system (Veltamat 3D now Uponor) has its own pump running, I think this pushes to the downstair, upstairs and room above garage, the extension has its own separate pump on the manifold.

The Heat Pump is a Grant Aerona 17kw. Below are our heat calcs:

SPACE HEATING ANNUAL HEAT DEMAND
Demand kWh/yr 24403
Heat supplied by HP, excluding auxiliary heaters kWh/yr 24403
Seasonal Coefficient of performance SCOP SCOP 4.22
Electricity consumed by HP, excluding auxiliary heaters kWh/yr 5783
Renewable heat supplied by HP kWh/yr 18620
Remaining heat to be supplied by auxiliary heaters and other heat source kWh/yr 0
Remaining heat, supplied by other heat sources kWh/yr 0
Remaining heat, supplied by auxiliary heaters kWh/yr 0
Electricity consumed by HP, including auxiliary heaters kWh/yr 5783

I've got the heat loss calculations, these are per room, is this what you mean?

We do have a Low Loss header fitted with the pump.

The weather compensation is turned on as of yesterday and is set at:

Maximum out going water temp in heating mode (Tm1) - 50 degrees

Minimum outgoing water temperature in Heating mode (Tm2) - 30 degrees

Minimum outdoor air temperature corresponding to maximum outgoing water temperature (Te1) - 0 degrees

Maximum outdoor air temperature corresponding to maximum outgoing water temperature (Te2) - 20 degrees

I can't post a photo yet as the forum doesn't allow me to post attachments yet (not sure if this is because I'm a new user!).

Thanks again!

Ash

@bn06amp

If you could post the heat loss calculations that would be highly useful, since the data should indicate how much heat energy is required by your home.

I am not that familiar with UFH systems, so I will have a look at the information for your equipment. My understanding is that UFH systems are designed to operate at lower water temperatures than would normally be used with radiators, to prevent any form of damage to the flooring. To achieve this they employ a mixing valve and additional water pump, and hence lower the temperature of the water going to the UFH heating coils. This would be the norm where you have both radiators and UFH, but seems rather wasteful in systems that only have UFH.

What indoor air temperatures do you desire?

As a start I would suggest setting your weather compensation to a LWT of 50C at an ambient temperature of -5C, and at the other end set a LWT of 25C at an ambient temperature of 20C. Monitor the room temperatures and the LWT and RWT whilst the system stabilises. Also monitor the energy consumption, which hopefully should start to reduce.

@derek-m I'm allowed to post pics now so please see attached!

This is based on a temperature in living areas of 21, this will be way too warm for us. So I'd expect roughly, downstairs 19 degrees and upstairs 18 degrees.

Hi Ash, welcome. Underfloor has a lot of thermal lag, it will take a day or so to get the thermal mass up to temperature. You should be able to get away with flow temperatures mid 30s if your house is reasonably well insulated and you run the ASHP 24/7 as is most efficient for UFH. Low loss headers - check they are balanced  - flow in across the top should match flow out across the bottom with all your heating zones on. You can do this crudely by checking temperatures in and out are the same either side. They do rob efficiency, but checking they are in balance and water is not short circuiting through it will minimise that. Adjust primary and secondary pump speeds or flow control devices to balance it. Ensure you have adequate flow, not less than Grant's installation manual data. For the 17kW at 35degC flow you need 51litres/minute.

If you have a low overnight tariff for electricity, forget using the ASHP for that and use direct immersion overnight on a timer and stat. The CoP is poor for hot water production as the ASHP needs to ramp up from 35degC to deliver water at 55degC to get the tank to about 50degC. Your flow and return temperatures suggest plenty of system flow, have you the Grant flow setter / gauge on the circuit anywhere to get some idea of primary circuit flow in litres per minute?

On/off controls of zones connected to ASHPs doesn't work, but this seems lost on Grant and their installers and recommended installs. The Grant unit controller is quite clever and can be configured and customised to suit your house. Grant tend to bypass all the in-built intelligence and connect it up to a dumb on/off main thermostat and dumb on/off hot water cylinder stat.

High consumption - yes, but we're in rather extreme weather right now, we all feel your pain! My Grant 10kW unit is defrosting about every 45mins and that's quite power hungry as it has to run more or less flat out for 10minutes or so after each defrost, no sooner has it got back up to my current 40degC supply temperature then it's back into defrost. It's not really operating at a stable control point as it would otherwise be. Add to that the reduced CoP due to low air temperature and you get rather thirsty units right now. SCOPs and COPs are all benchmark tested at 7degC, which means no defrost. In reality, the weather we have now is maybe 3-4 weeks of a year in total, and we're getting a 2 week continuous block of it.

@allyfish Thank you for this, I appreciate such a detailed response and how much time this must have taken you!

I've attached a picture of the low loss header, I'm not sure what to measure (also do you mean measure the temperatures on the pipes manually with a thermometer? Apologies if thats a really silly question!)

With regards to the flow rate on the pump, how do I check what this is set to? Is this something in the Control panel?

We've got an immersion set up for the hot water, would I be best using this every night for an hour (at the moment the pump is set to heat our water overnight for an hour, which as I understand it, means the heat pump stops generating for the UFH and directs everything at the water). If I set the immersion to run for an hour each night, would this then stop the heat pump from diverting to hot water? (i.e. pump would run the UFH all night

as water would be heated with the immersion, rather than the pump?)

On the thermal lag, the house is not yet to temp, but is very gradually getting there - once I'm up to temp, would you suggest then maybe starting to knock down the weather compensation maximum, would a couple of degrees a day be too aggressive?

I also have a 17Kw grant. But I think your heat loss claculation you showed it was 24kw.  The Grant, like all heat pumps will have much less, probably 12 to 13kw output at O degrees or less. If I am correct your heat pump may be far too small.

I knew mine was  too small for very cold weather when it was installed. (Had limitations on mains cable size to the heat pump location to put in 2 heat pumps). If all 19 radiators are on, at 0 deg outside, the raditaors cannot get above 35degrees and house is too cold. If I turn off around 5 radiators,  the rest will warm up to 50 deg and those rooms get very warm. Some of the TRVs then close down and I can then turn one or two of the other radiators. 

I have it off overnight and consumption is around 50KW per day in this very cold weather

Do check it defrosts corectly, maybe every 40 minutes when it is below about 5 deg outside. Mine was not sensing it quickly enough but after Grant changed a board it was fine.  

@bn06amp yes, with a thermometer (you can buy little digital ones with small probes) check the temperatures are comparable across the top pipes and the bottom pipes of the low loss header. It's not very scientific, but would let you know if there's a large imbalance on the primary and secondary sides. The Grant unit prioritise hot water over heating, so whenever hot water is scheduled, you lose heating. Losing heating into an underfloor system for an hour isn't that bad, you notice it more with wet radiators as they lose heat and go cold very quickly. There's a lot more latency with underfloor. If you have the cheap tariff, use that via the immersion and clear any programmed time periods for hot water on your Grant controls. Or simply turn the hot water programmable time clock to off.

I see you have a secondary return & pump (orange pump) on your hot water system. That gives you hot water on demand quickly at taps distant from your tank, but it does consume energy 24/7, both the energy taken by the pump, and the energy lost through circulating hot water continuously through the pipework.

@allyfish Thanks again! The secondary flow is on a timer too, it only come on each evening (when typically we'd be getting showered), so would this mitigate what you mentioned above?

Our floors are still getting up to temp but are gradually increasing, I'd imagine I've chose a bad time to be trying to get everything back up to temp when it has been -5 outside!

With regards to the hot water demand, my understanding was that as soon as the tank is up to temperature, the demand for hot water would stop (even if there was time left on the schedule) and switch back to heating, is that correct? I've set the immersion to come on in the night, prior to the hot water schedule on the pump, so was hoping that this would effectively disable the hot water schedule on the pump? If not, then I'll need to delete the time zones from the HW controller.

I've knocked the Weather comp back today and as of yet doesn't seem to have had any detrimental impact on the flow temperatures.

I suppose my overarching question on all of this now is, should I now expect my electricity  usage to drop, the current levels that this is running at, bills wise, really is causing us quite a lot of stress. I do appreciate the rather extenuating weather, but even prior to this the pump was still being quite hungry (albeit everywhere was zoned and set to come on and off).

@bn06amp ah, having the secondary hot water pump on a timer is a good idea, to only use when needed. You're right about the ASHP and hot water demand, when the cylinder demand stat is satisfied, the ASHP will revert to heating. Similarly, if the immersion has warmed the water up beyond the stat control setting, the ASHP will not need to switch over to hot water.

The way Grant set up the heating and hot water controls isn't very clever. Each time the hot water demand switches over on my system the circulating pumps and compressor stop, the motorised valves change over, and the pumps restart. Then after a time delay the compressor restarts. It's very primitive.

The hot water and heating are both on the secondary side of the system after the low loss header. The primary pump and ASHP compressor could continue to run, the secondary pump could stop, briefly, while the 2-way valves on the tank change over. That would be much more efficient and less disruptive to the refrigeration system inside the Grant ASHP. Grant seem to fit dumb external on/off controls for heating and hot water to the much cleverer ASHP controller, but that's symptomatic of the installers' competence level, their familiarity with simple timed controls and unfamiliarity with ASHP controllers. I suspect if the Grant AHSP controller was controlling both heating and hot water directly, with no external room thermostats or hot water timers connected to it, it would do it in a more efficient manner or be capable of being configured that way.

Getting rid of on/off controls that frequently turn the whole ASHP on and off, and dropping the heating supply temperature will definitely improve efficiency and reduce running cost. As your underfloor warms up, the return temperature to your ASHP will raise, and the unit will modulate down. The biggest single impact will be the end of this cold snap however, once we get back to seasonal average temperatures, when the ASHP will be a little happier and defrosting a lot less. The Achilles Heel of ASHPs is that they are least efficient in the coldest weather. It's not a perfect technology, and GSHP has an obvious advantage there. But, during the milder heating months of Spring and Autumn, the efficiency can be very high and the running costs very low.

I'm in the same boat. My first winter with ASHP and my electricity usage all-in for this month so far is 500kWh or £181. I reasonably expect a month-end bill of £350. November was 607kWh or £220 all in. We need to think about the total bill for the year and not focus too much on day-to-day running costs. I would have been burning a lot of kerosene previously to heat my house, but with no simple means of monitoring how much.

@allyfish Really useful again, thanks! What size pump do you have and what is the Sqm yours is supplying? Over the weekend, prior to making the changes to all the zones and actuators, our overall electricity usage was running at about £25-30 per day 😣 

I've starting to knock down the weather compensation curve today - the system seemed to be topping out the flow at about 44-45 anyway. I've set the maximum end to this at 48 with an external temperature of -2. I'd imagine, it can probably go down a little bit further, and I'll prob go half a degree - a degree a day over the next few days, hopefully as I do this then the defrost cycles may also reduce as well.

I'll also make the changes to the HW system so that this stops switching overnight. Does anyone have any idea how long an immersion should be on to heat a 300l tank? I.e. how long should I have the immersion on each night?