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Another cheap 12kW Kingspan Aeromax ASHP

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3 minutes ago, JSHarris said:

The main problem is that the default weather compensation curve results in a fairly high flow temperature, certainly mine was too high on the default setting and that resulted in severe defrost cycling.  I ended up removing the weather compensation altogether, and programming in a constant flow temperature, as that makes a great deal more sense for a low energy house with UFH, where you're mixing the flow down to around 25 deg C at the most.  Mine is set to run at 40 deg C maximum flow, no matter what the outside temperature, and that gives no defrosting at all in our installation, which improves the real-world COP by a lot.

I have never understood the need for weather compensation.  Presumably this is done with a temperature sensor built into the unit?  If it were an accessible sensor then I would be inclined to remove it and replace it with something fixed / adjustable as a n easy way to set the flow temperature.

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Yes, there is a temperature and humidity sensor on the rear of the unit.  It's used to control the defrost cycle, as well as the weather compensation curves.  I'm pretty sure that weather compensation is just a hang over from energy saving controls for high heating demand homes, and it is a waste of time for a low energy home with UFH.

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3 hours ago, ProDave said:

Is the 6KW the electrical input rating, or the heat output rating?

 

The 6kW is the approximate peak output, the max electrical input is 2kW.  In practice the input will rarely exceed 1kW I've found, ours tends to run at around 400 to 600W electrical input power when on.

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Not my bid. But before I do bid, what do thee units normally retail for?

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4 minutes ago, ProDave said:

Not my bid. But before I do bid, what do thee units normally retail for?

 

They were usually around the £2500 to £3000 mark I think.  Installed price was a lot higher, and I have a feeling that Kingspan only sold them as an installed package.  I paid £1700 (delivered, inc VAT) for a brand new unit, including the Command Unit, from a dealer that was closing down, and he told me that was the wholesale price (not sure how true that is!).

Edited by JSHarris

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3 hours ago, ProDave said:

I have never understood the need for weather compensation.

 

3 hours ago, JSHarris said:

I'm pretty sure that weather compensation is just a hang over from energy saving controls for high heating demand homes, and it is a waste of time for a low energy home with UFH.

I disagree about the relevance of compensation in a low energy house, the principle is the same as with a normal house just that the range of flow temperature is lower as you lose less heat. The point is that low energy houses still lose heat.

 

ASHP is much more efficient when running at a low flow temperature. If you set static flow temp for a cold winters day at (e.g.) 28C then as the external temp goes up your flow is still 28C, but could be much lower to achieve a balance between heat input and heat loss. You end up cycling the heat pump.

 

If you adjust flow temp to balance the input to the loss (which is what weather compensation does), you can run the system on all the time with minimal cycling and lowest flow temp to achieve highest COP.

 

Now the saving is not likely to be massive in a low energy house, but as weather compensation seems to be built into these units in any case then why not use it? Costs no more.

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8 minutes ago, ragg987 said:

I disagree about the relevance of compensation in a low energy house, the principle is the same as with a normal house just that the range of flow temperature is lower as you lose less heat. The point is that low energy houses still lose heat.

 

The issue is weather compensation only works for heating.  A lot of us in Low Energy houses have/are using the ASHP as a pre-heat for DHW and just tapping the house heating off that.  In this case you want a constant flow of around 40C for your pre-heat/(TS)/whatever you are using.

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10 minutes ago, ragg987 said:

 

I disagree about the relevance of compensation in a low energy house, the principle is the same as with a normal house just that the range of flow temperature is lower as you lose less heat. The point is that low energy houses still lose heat.

 

ASHP is much more efficient when running at a low flow temperature. If you set static flow temp for a cold winters day at (e.g.) 28C then as the external temp goes up your flow is still 28C, but could be much lower to achieve a balance between heat input and heat loss. You end up cycling the heat pump.

 

If you adjust flow temp to balance the input to the loss (which is what weather compensation does), you can run the system on all the time with minimal cycling and lowest flow temp to achieve highest COP.

 

Now the saving is not likely to be massive in a low energy house, but as weather compensation seems to be built into these units in any case then why not use it? Costs no more.

 

 

Sorry, but I'm not sure this adds up.  The maximum flow temperature of our UFH is around 25 to 26 deg C, in really cold weather.  The heat pump can't modulate down below about 1.5kW output, and even that is close to the maximum  heating demand for the whole house in very cold weather.  It also has short cycle protection, so it shuts off for around 20 minutes when that kicks in.

 

This means that a buffer is needed, just to give the heat pump a decent load to work into when it's on, and to store heat energy when the heat pump is off.  Running the heat pump at a constant low flow temperature (in our case 40 deg C) is the point where it's most efficient.  Turn it down to the lowest (about 30 deg C) results in short cycling, even with a 70 litre buffer, and that tends to reduce the real-world COP.  The COP is maximised when the heat pump runs for fairly long periods, with no defrost cycles.

 

I ran loads of experiments with ours (same as this model, a re-badged Carrier) and determined where the best efficiency point was.  It turns out that, with a constant 40 deg C heat pump flow temperature the COP is near-constant over a pretty wide outside air temperature range, when heating the house.

 

I did try several custom weather compensation curves before doing this, and what we've ended up with is what works best, by a fair margin.  The weather compensation in these units is crude, it just increases the flow temperature in a linear relationship to the outside temperature - all you can change are the fixed points on that straight line.  It does not control differential flow and return temperature directly at all, there's not enough headroom to do that.

Edited by JSHarris

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The item on Ebay does not know include manuals or installation kit! According to the blurb.

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Ours came with no installation kit, but it's not needed.  All you need are a couple of long flexible hoses, plus a Y strainer to fit inside the house on the return pipe.  I made an error by not using long flexible hoses, in a loop, as shown in the installation instructions, and had a noise problem, from vibration transmitted through the hoses.  Swapping the short (and too stiff) ones out for long ones fixed the problem completely.  The hoses I used were standard large bore ones, that I think came from Pipestock.

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In our case (330m2 house to PH standards for insulation and air leakage) flow needed to go to about 30C last winter on the colder days. We only commissioned in October so perhaps house is still drying out and not in steady-state, I intend using the next winter to fine-tune and validate our setup.

 

26 minutes ago, JSHarris said:

I ran loads of experiments with ours (same as this model, a re-badged Carrier) and determined where the best efficiency point was.  It turns out that, with a constant 40 deg C heat pump flow temperature the COP is near-constant over a pretty wide outside air temperature range, when heating the house.

How are you measuring COP? The Hitachi unit I have does not have a readout for this, though it can estimate output energy over a period of time. I think the gap is it does not know input energy. If there is a simple way would love to try it.

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Our glowworm one didn't come with the control pack or installation kit either. I was hoping to connect it straight on to the uponor plastic pipe but will see how it goes when we are installing. 

 

Edited by Alexphd1

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7 minutes ago, ragg987 said:

In our case (330m2 house to PH standards for insulation and air leakage) flow needed to go to about 30C last winter on the colder days. We only commissioned in October so perhaps house is still drying out and not in steady-state, I intend using the next winter to fine-tune and validate our setup.

 

How are you measuring COP? The Hitachi unit I have does not have a readout for this, though it can estimate output energy over a period of time. I think the gap is it does not know input energy. If there is a simple way would love to try it.

 

I just fitted a energy/power meter to the electrical input and as a part of the house data logging I have temperature sensors on the flow and return pipes that are logged every 6 minutes.  The flow rate is constant when the system is running, so it's fairly easy to calculate the power output at any time.  The COP never drops below 3.2 and most of the time it's around 3.8, peaking at a bit over 4 occasionally.

 

The energy/power meter I used is a standard DIN rail mounting one, that measures power, energy, frequency, power factor, voltage and current, and was pretty cheap, around £20 I think.

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Here's the default Temperature Compensation curve from the Kingspan manual (Outside Air Temperature Vs Leaving Water Temperature)

 

 

Capture.JPG

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That looks the same as the one I have, but is drawn the other way around.  The problem I found was that when the outside temperature drops below about 3 to 4 deg C with the default curve, the heat pump would start doing defrost cycles, where it reverses and sucks heat out of the house to melt the ice.  These last around 10 minutes or so, and really hit the COP badly.  The worst case outside temperature seems to be in the 0 deg C to 4 deg C range, when the outside humidity may well be high enough to cause a lot of condensation and potential ice build up.  Below about -2 deg C the efficiency starts to improve, as the air will be drier and so there's less need to defrost.  By the time the temperature is down to about -5 deg C (rare here) I don't think it would need to defrost even if run at a flow temperature that's  a fair bit higher.

 

As mentioned in other threads, defrosting is the performance killer, so ensuring that the heat pump doesn't have to work too hard in cold weather has a big benefit.

Edited by JSHarris

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16 minutes ago, Alphonsox said:

Here's the default Temperature Compensation curve from the Kingspan manual (Outside Air Temperature Vs Leaving Water Temperature)

 

 

Capture.JPG

That does look bonkers and would leave the poor thing trying to deliver water at 55 degrees for a lot of the winter here.

 

Once you have set your chosen (straight line?) compensation curve is it remembered for good (i.e if you can't buy a controller could you borrow one just to set it up then return it?_

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I wouldn't necessarily discount weather compensation. We used it in our last house where the flow temp reached a max of 33C at 0C ambient, and in our new house.  I only have limited data for the new house, but COP when we were still needed heat input ranged between 3.5 and 4. I certainly found the trick was getting the right (fairly flat) curve, but that is simply a case of trial and error and relates to the particular microclimate you have.

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14 minutes ago, ProDave said:

That does look bonkers and would leave the poor thing trying to deliver water at 55 degrees for a lot of the winter here.

 

Once you have set your chosen (straight line?) compensation curve is it remembered for good (i.e if you can't buy a controller could you borrow one just to set it up then return it?_

 

Yes, it remembers it permanently.  There are (IIRC) four set points, that match up to the ends and the two corners in that plot.  I remember sketching it out on a blank page in the manual, in order to get my head around what each of the four settings really did, as the description for setting custom curves in the manual I had wasn't very clear.

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If you can re-programme it, this kind of price seems like a great deal even if its only for some supplementary space heating. What are the output options?

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32 minutes ago, gravelld said:

If you can re-programme it, this kind of price seems like a great deal even if its only for some supplementary space heating. What are the output options?

 

Two pipes, a flow and return.  The flow delivers water (inhibited, with antifreeze) at the programmed temperature, the return takes the cooler water back.  It can be considered to be a low temperature boiler, and wired and plumbed in much the same way inside the house.

 

Electrically, all it needs to run is power plus a dry contact programmer/thermostat, much the same as any other heating system.  To programme it the Command Unit is needed, as that allow loads of settings to be changed.

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Is there an easy setting (volt free contact?) that will allow you to change the set point, e.g 40 degrees for UFH and 50 degrees for DHW?

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2 minutes ago, ProDave said:

Is there an easy setting (volt free contact?) that will allow you to change the set point, e.g 40 degrees for UFH and 50 degrees for DHW?

 

Yes, dead easy.  There is a DHW mode that can be activated by a dry contact between the 12V common and the DHW connection.  The diagram I drew up a while ago, and posted here shows the connections:

 

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Well I didn't win this one. It went higher than I was prepared to pay for a unit with no guarantee and dubious past.

 

Anyone here win it?

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I did have a few cheeky bids in under £400, but that was my limit!

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