Air Source Heat Pump - need heating advice

[MartynP]

Hi all,

 

I had a Mitsubishi Ecodan 8.5kw and Mitsubishi pre-plumbed 250L tank installed a few months ago. Although I did the research on installers and read many reviews in the process I did find an installer I believed was good, well the install was good but let's just say the after sales advice is somewhat lacking.

 

A bit of background, I live in the south east in a 4 bedroom three bathroom house, as I've extended it over the years. It's a 1985 construction with double glazed UPC doors and windows, cavity wall installation, and approx 300-350mm of loft insulation. The house is all radiators that are K22(?) type, double paneled with 2 sets of fins and the heat loss calculation shows they are the right size for the house and ASHP, I'd also say we are reasonably air tight with no drafts anywhere.

 

After a number of visits post install it was left on weather compensation mode and the LCD display showed it had been set at +9. However, the house never seemed to get warm so after a call to the Mitsubishi customer help line they said the best setting would be flow temperature and suggested trying around 45 degrees. Using MelCloud I've been trying to keep track of how much it's costing for heating, especially as my supplier went bust and below is what I've been recording. The outside temperature is from a temperature logger I bought off Amazon for about £15 and records the outside temperature every 10 minutes or so  

 

Date	Consumed	Delivered	Ave Temp	SCOP
16/12/2021	12.8	51	11.9	4.0
17/12/2021	16.1	70	8.5	4.3
18/12/2021	16.6	68	8.7	4.1
19/12/2021	14.8	62	5.3	4.2
20/12/2021	18.7	84	6.6	4.5
21/12/2021	21.2	88	5.8	4.2
22/12/2021	27.8	92	2.2	3.3
23/12/2021	18	79	8	4.4
24/12/2021	15.3	64	8.6	4.2
25/12/2021	21	82	6.7	3.9
26/12/2021	19.9	76	7.2	3.8
27/12/2021	21.9	81	9.8	3.7

 

I've struggled to work out if weather compensation or flow control is the best from a comfort/cost perspective. Despite reading a number or articles or watching youtube videos I've also struggled how to set up weather compensation so it heats the house sufficiently. Can anyone who has experience of this setup advise in the real world what I should be aiming for?

 

Thanks in advance

Martyn 

 

[ProDave]

The idea of weather compensation is to reduce the temperature of the delivered water when less heat is required to improve the COP.

 

Personally i maintain that to set that up you need to know some data about the performance.  So what you first need to find out, is on the very coldest days in winter, what flow temperature do you need to get the house up to the required temperature.  Only then when you know that can you begin to play with the weather compensation curve, experimenting with the other end of the curve to see how much you can reduce the temperature by in mild weather.  So for this season at least stay with compensation off.

 

If you are really running at 50 degree flow temperature, those COP figures look good.  How are you calculating the COP? or what is measuring the "delivered" power?

 

The big question to start with, is with a constant flow temperature is the house getting hot enough?

[IanR]

7 hours ago, MartynP said:

The house is all radiators that are K22(?) type, double paneled with 2 sets of fins and the heat loss calculation shows they are the right size for the house and ASHP,

 

Hi, and welcome.

 

What flow Temp did the calcs estimate is required for the size of radiators you have installed? Is the ASHP achieving that temp? and what is the return temp when it does achieve the set flow temp?

Are you leaving your heating on for the majority of the day, or are you scheduling it for a couple of periods during the day (as you would do if you had a gas boiler). On the coldest day in your data the ASHP could have delivered that energy in around 11 hours of running, which suggests there is some headroom where it could deliver more energy/heat.