@derek-m looks like it works. As an FYI you can use the formula FORECAST in Excel to estimate a data point from available data e.g. off number temperatures and COP

Hi Everyone,

I have been carrying out further assessment of the data along with performing various 'what if' scenarios, these

are detailed on sheet 2 of the attached spreadsheets. There are two spreadsheets, for the 12kW ASHP and the 14kW model, so that comparisons can be made.

I have added an additional column to sheet 1 labelled COP - LWT. The upper value at each outdoor air temperature value is the anticipated COP at the calculated LWT, which is the middle value in the column. The lower value is the Power Input (PI) at the particular COP and LWT values.

As before, the parameters on line 1 of sheet 1 can be varied to ascertain the effect that they would have on the heating system.

Let me know if there are any other scenarios that you would like to be checked out.

@derek-m I do have a calculated heat loss with room by room radiators - would this be useful in your scenario? Our primary living is in one room (12m x 6m) of which the largest losses are via the bi-fold doors.

@derek-m below is the 90th percentile coldest day where I live. Its very mild here as we are on the coast and I imagine this would have a big effect on the heat demand calculations.

Hour of the day     Outside temp
24 / 0                         1.5
1                                1.2
2                                1
3                                0.8
4                                0.5
5                                0.5
6                                0
7                                0.2
8                                0.5
9                                1
10                              1.5
11                              2
12                              3
13                              3.2
14                              3.5
15                              3.5
16                              3.5
17                              3
18                              2.8
19                              2.5
20                              2
21                              1.8
22                              2
23                              1.8

Hi Batalto,

I have put your temperature readings into the spreadsheet with the attached results.

Because I don't have the data for your heat loss and the total output of your heat emitters, I used the values shown in row 1 of sheet 1.

The sheet labelled Data gives the results for the data supplied.

You can do the assessment yourself in the following manner.

In row 1 of sheet 1 change the Heating Demand to your heat loss value, set the desired indoor temperature and change the Total Heating Elements Output to the sum of all your heating elements.

On the Data sheet clear cells C8 to Z10.

For each time period as shown on the Data sheet, note the outside temperature and then change the most appropriate Outdoor Air Temperature value in column B on sheet 1 to this value. e.g. for the first time slot change the 0 in cell B18 to 1.2.

Then read the corresponding values for COP, LWT and PI from column C and put these in the relevant cells in the Data sheet.

Repeat this operation for each time slot, until all the cell are filled in the Data sheet.

The totals on the Data sheet will now indicate the energy consumed (PI) and the Heat Energy produced by the ASHP along with the average COP value.

I hope that this helps.

@derek-m thanks for that - as an FYI our heat loss is 8774w and our emitters are 12,115w in power

From this, on the coldest day of winter we would use 64kw of power to heat the house. Although that's keeping the whole house at 21 for the whole 24 hours. Realistically we would drop that to 17/18 at night (at least in the bedrooms). However the issue with our house remains the largest room is the one that loses the most heat due to the bifold doors - however the bedroom is directly above it. Heating that room to 21 would mean the bedroom above is also 21. Its going to be interesting playing around with the system in the winter to get the best performance.

That day I provided to you is in the 90th percentile - so a very low chance of happening over a long period. I'm going to see if I can build a tracking system with a CT clamp to track use every 1 minute, then I can relate back to COP.

Hi Batalto,

I have carried out various scenarios based on your data, which are detailed on the Data sheet.

One of the scenarios is improved insulation. To help prevent heat seepage into the bedrooms, would it be possible to fit insulation boards to the ceiling in the main room?

As an experiment, during the Winter, you could try fitting Stormguard Secondary Glazing Film at the bifold doors to help reduce the heat loss. If it proves successful, a more durable arrangement would be to install a clear perspex sheet during the Winter, which can be removed during warmer weather. It is something I will be trying on my office window this Winter.

As you will see from the data, improving your heat emitters could reduce your energy consumption by almost 25%, unless they are already high output devices.

Have a look at the data and let me know what you think.

@derek-m we already have 200mm of rockwool between the floors. It's more just an issue that the top of the house is super insulated so hangs onto heat like no one's business. We use a 3 tog duvet all year and don't even bother turning on the heating 90% of the year upstairs. 

Hi Balalto,

Rather than install air conditioning upstairs, you could consider fitting Mechanical Ventilation Heat Recovery (MVHR), which could be used to regulate the temperature in the bedrooms. It may also be possible to duct the warm exhaust air from the MVHR to the air intake of your ASHP, in that way improving its efficiency.

@derek-m We've considered MVHR before, however I've seen that the gains are pretty negligible in terms of cost vs payback. Given our main room is the hardest to heat I might look at K3 (or other type) radiators after the winter. Lets see how the heatpump performs first. First thing I need to look at is the controller and how I might be able to use the main controller downstairs and the nest upstairs - especially given as we barely use the heating upstairs.

Hi Batalto,

I think that I may have misunderstood your problem. I assumed that you were having a problem keeping your bedrooms cool rather than being able to bring your main room up to temperature.

Whilst analysing the data that you kindly provided, I researched suppliers of high output radiators, which led me to the site JustRadiators. There I found a selection of Ultraheat type 33 / K3 radiators, that according to their specification give the highest output, per unit size, that I have so far been able to locate. They are also quite reasonably priced.

Alternatively, you could consider radiator booster fans. These sit on top of your radiator and help increase the airflow and hence dissipate the heat energy in a more efficient manner. We tried one in my wife's 'woman cave' and she seemed quite happy with the result. It is difficult to quantify how effective they are without carrying out very detailed measurements over a period of time.

If you have radiators on outside walls, you could also consider fitting Radiator Heat Reflector Back Foil.

What size and type are your present radiator.

Hi Everyone,

The attached spreadsheet shows the results of performing various 'what if' scenarios on the data for a Midea 12kW ASHP. By looking at percentage change rather than actual values, it may be possible to expect similar results with ASHP's manufactured by other companies.

The calculations were performed on a hypothetical property and under specified operating conditions, so that meaningful comparisons could be made. No allowance has been made for solar gain or the effects of wind chill or cooling due to rain.

I personally draw the following conclusions from the analysis.

1) To ensure reliable operation over all anticipated weather conditions an ASHP should have a specified output rating of approximately 1.75 times the calculated heat loss of a given property.

2) Close attention should be paid to how the manufacturer's version of weather compensation is designed to work, and how well it is able to adjust the operation of the ASHP to cope with changes in weather conditions.

3) Improving insulation levels should be a priority.

4) To help keep energy consumption to a minimum heat emitters with the highest output rating should be installed where possible, though it may be necessary to make compromises for system balancing.

5) Lower the desired indoor temperature to a level you find personally comfortable, and at which you do not suffer marital discomfort.

6) Major energy savings could possibly be made by capturing solar energy to be used to improve ASHP efficiency during colder periods of the day. I don't know of any commercially available system at the moment, but I can provide a detailed design for anyone who may be interested in building their own.

7) A further possible way to reduce energy consumption would be to employ a large buffer store. This could be heated during daylight hours when the ASHP is operating at it's most efficient, the stored energy could then be used during the colder nighttime period to reduce the load on the ASHP.

I welcome any questions and comments.