UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

paceinternet

bushyh, I would suggest you ask the supplier to make clear what temperatures the system is designed to operate at.
Example:
-10 degC outdoor air temp
Room temperature: 20 degC
Heat loss: ??? say 7kw
Water flow temperature: ??????? 35 , 55 degC

By asking this, you should get confirmation that the radiators/ufh/fan convectors can provide enough kw to maintain the room temperatures.
Then when they tell you the water temperature necessary for the room temperatures, you can ask to see the "specific performance curve" to confirm that the heat pump can deliver those kw at that outdoor air and water flow teperature.

If you haven't yet recognised, there is a conflict in raising the flow temerature which reduces the kw output. See the Calorex doc link posted above on P23. At Air 0 degC, 35 degC water gives 9.11 kw, and at 55 degC water it is 7.86 kw. At Air 7 degC, 35 degC water gives 11.7 kw. So at -10 degC, 35 degC water might be < 7 kw and at 55 degC it might be < 6 kw.
You might need the higher water temperature for the radiators to dissipate the required amount of heat into rooms, but the heat pump will deliver less kw at the higher temperature.

richardc1983

paceinternet wrote: »

You might need the higher water temperature for the radiators to dissipate the required amount of heat into rooms, but the heat pump will deliver less kw at the higher temperature.

Even if the flow temp was brought down the heatpump is only raising the water Upto 33c ish which isn't enough for heating the house so if it was lowered it wouldn't have any effect. Perhaps if there was under floor heating it would have made sone difference.

richardc1983

bushyh wrote: »

Really useful information which I have kept thanks. I have been on the phone to the builder today, not shouting and screaming yet but asking for the technical report being done following the visit last week. I have put in his head gas boiler/different pump scenarios but knowing that nothing will get done this side of christmas am happy (not the right word really) to wait a couple of weeks rather than people rushing into things after their Christmas parties!! Your data I intend to throw at him when the calorex report is received. Meanwhile I put the booster on at 4.30pm went to check water temp 2 hrs later - at the time the defrost setting was running and temp was at 44, once that stopped it went down to around 38, it was increasing slowly but at that point I decided I had enough of waiting in the cold! My lounge is at 15.4 which is exactly what it was on when I arrived home from work. I guess the booster isn't doing much although the outside temp. will be dropping. I am trying to avoid using the convector heater today so I can see what the meter reading is without that. Is the idea of the 55 SP temperature to have it high in the winter but lower during the milder weather so energy costs are less. My understanding was that the control panel was for the engineers rather than me and that it wasn't something to be meddled with. I am assuming there is no point in reducing that to reduce the cost if we are not getting up to that temp anyway?

I would agree there is no point lowering it, the only time I would lower it is if you was getting enough heat at the higher temp you could then reduce it until it holds is own.

You can alter the settings your self as you please it's just like the settings you would have on a gas combi boiler really.

-12 here tonight and were maintaining 23c here. When the system goes off you can feel the cold permeating through the walls and floors so we have had to put it up a bit to avoid this.

paceinternet

Even if the flow temp was brought down the heatpump is only raising the water Upto 33c ish which isn't enough for heating the house so if it was lowered it wouldn't have any effect. Perhaps if there was under floor heating it would have made sone difference.

But that is the point of my post. If the radiator part of the system was designed to work at water temperature of 35 degc at some outdoor temperature, then, there is a problem with the size of radiators.
If it was designed to be at 55 degC, then the problem is with the heat pump because it can't make that.
If it was all designed for an outdoor temperature of 0 degC, then they need to prove it at 0 degC, but they also need to explain the strategy for dealing with - 10 degC.

bushyh

paceinternet wrote: »

But that is the point of my post. If the radiator part of the system was designed to work at water temperature of 35 degc at some outdoor temperature, then, there is a problem with the size of radiators.
If it was designed to be at 55 degC, then the problem is with the heat pump because it can't make that.
If it was all designed for an outdoor temperature of 0 degC, then they need to prove it at 0 degC, but they also need to explain the strategy for dealing with - 10 degC.

i am in the process of putting all my temperature and meter readings on a spreadsheet and will also find average local air temperatures to go on it. I will then forward this to builder and a version of your comment above which is simply put thank you.

thechippy

There are three possibilities...

1. The heat pump is not working correctly
2. The heat pump is undersized for the application
3. The rads are undersized

My bet is number 1 or 2....;)

zeupater

thechippy wrote: »

There are three possibilities...

1. The heat pump is not working correctly
2. The heat pump is undersized for the application
3. The rads are undersized

My bet is number 1 or 2....;)

Hi

What would make you suggest that "The rads are undersized" ? .... surely if it was anything to do with radiator size the opposite would be the case ....

A more probable option would be ... "4. The heat pump is not suitable for operation in extremely cold weather conditions" ... as per the manufacturers literature "Calorex heat pumps which are MCS approved have been specifically designed for optimum operation in the UK’s maritime climate.", the key phrase being 'maritime climate'.

I can only think of two reasons why you would include that phrase in the literature .... firstly, the ASHP has been specifically designed to cope with the higher humidity which prevails in maritime areas and therefore copes better with ice formation on the outdoor unit ... or ... secondly, the ASHP is not suitable for use in areas which experience continental extremes in weather .....

So, to me, 1 or 4 are the most likely.

HTH
Z

thechippy

If the rads have been sized for a flow of 55, but the heat pump can only deliver 35, then the rads are undersized.

From the quick look I've had, Calorex give no spec for temps of less than 0c. It seems to me this is a half hearted attempt at a domestic air to water system.

In any event, I think this is undersized for the application.

bushyh

Calorex director has not submitted his report to the builder yet but response so far is

'He did say that the early indications are a frost sensor and possibly another ASHP will be his solution but he does need to do more investigative research.'

I wonder if he should come on here and do his research, seems like he might get some answers like go and work for a different manufacturer perhaps!

Cardew

People should read the EST report for field trials on Heat pumps - particularly on ASHPs. http://www.energysavingtrust.org.uk/Generate-your-own-energy/Heat-pump-field-trial

The study was a year long and had 29 ASHP systems from a number of manufacturers.(who installed the systems)

It is quite a long report but of the 29 ASHP systems the annual COP for 19 of the systems was 2.2 or less(the highest number had a COP of 1.6). So if that is a average spread across 12 months - little wonder systems are struggling in this current weather. In fact with the requirement for wasteful defrosting cycles, it is quite easy to envisage a situation with some systems where there will be a COP of less than 1.0 and people would be better to switch off the ASHP and rely on Granny's old 1/2/3 bar fire!!!!!!

It is also most important to note that they state because of the low water temperatures, the heating must be on much longer. This for comparison with gas/oil etc further weakens the case for ASHPs. For people who are out of the property or in bed, there is no need to have gas/oil heating on until, say 30 minutes before they get back in the house/get up; so little wasted heat. Not so with an ASHP as it has to be on for many hours while the house is unoccupied/people in bed.*

If our sensitive contributor thinks the above is Troll behaviour he should read the report and complain to EST!

* to explain if an ASHP output is, say, 150kWh in a day, that is far less effective than a gas CH output of 150kWh as the latter(with water at 80C+) is used when it is required - not when people are out or in bed.

** The COP figures quoted above are strictly speaking the overall system efficiency i.e. kWh in and kWh out.