Control of Air Source Heat Pump

[DiggerJ]

I have a CH/HW system with 6 stats, some of which are programmable all at £240V. They control my Oil Fired boiler System.
I am having an ASHP fitted which I want to control with the existing 240V timer/stat control system.
The ASHP has a pair of terminals (Currently looped) as part of its 12V system specified for connection to "Timer/stat"
I think that I ought to be able to connect a Relay that activates the 12V control circuit when there is a demand from the existing system.
My intention is to manually switch between boiler & ASHP depending on weather conditions.
Which Relay would be appropriate?
I hope someone can help

 

[DiggerJ]

I'm sorry the £ sign should not be in the 2nd line

 

[efficiencyman]

I have used 230V coil with 10 A DP DT cantacts from ebay under £10 the DP is used to separate the 2 heat sources. The circ pump is then controlled from either NO or NC -- easy ! The coil is operated by digi-stat from outside ambient which I set around 4 to 5 Degs C to avoid the evaporator from icing over, it costs to melt ice so don`t let it ! After much experimenting it can work very well, my system has been working since 2012 I am pleased with my investment, total outlay £2500 for 15Kw whole house ASHP and installation including a 2nd hand buffer tank ( self install ).

 

[DiggerJ]

Thanks very much - it conforms what I suspected was the right solution in principle. Now I can get down to it I practice!

 

[efficiencyman]

Another tip, make sure your ASHP built in frost protection will override any circ. pump control of Oil burner timer even if its timer is OFF, the relay must failsafe NC. i.e. the circ. pump needs to also run from the frost protection stat. Will your plumber be fitting separate circ. pumps for each heat source ? If so M/V`s may be needed to ensure correct flow is not bypassed. Then you may need to have another relay for the M/V`s

 

[DiggerJ]

Thanks again
I will make sure about the frost protection point
Re pumps: We will have separate pump and think that check valves on each heat source will do the trick. They may even allow both heat sources/pumps to run together; but that is for the post-operational experimental phase

 

[TJ Anderson]

I done a few ASHP's but it was about 8-9 years ago now and they may of moved on now with regard to flow temps. Back then the Ecodans also had boilermates and FTC's to assist. Also Rads were upsized for lower temps. Is that ASHP sufficient to get the stored HW hot enough (over 60) with regard to legionella or is it just a simple Boiler to ASHP swap out now?

 

[efficiencyman]

Regards the good point TJA has mentioned. Yes don`t run the HP over 50 (unless your having one of the latest expensive types that are coming on the market now ) but that`s another topic in itself.
It`s a good idea as TJA has said, you could have a timer that brings on the Oil burner at least once a week to above 60 Degs. C. that`s what I do with my Gas boiler Hybrid. My Rads are mainly oversized & with some underfloor. I also only pre-heat my DHW with the ASHP or my Solar thermal which has worked well for 26 years now.

 

[DiggerJ]

Yet another helpful point in the management of the system, so thank you again.
Actually, my system also has a pre-heat tank for our downstairs hot water - heated with basic DIY solar water panels (radiators under glass on South facing side of house) I shall take on board all these very helpful comments. I can't thank this Forum enough!

 

[Leesparkykent]

or an immersion and timer

 

[efficiencyman]

or an immersion and timer

On what Lee ? Is that off peak Leccy ?
Some of us want a better return on 12 p / Kwh than 3Kw in = 3Kw out !
Heat pumps are about obtaining more out from less input. Typically 4 Kw out from 1 Kw in or at least better than cheaper Gas with 30% of that up the flue !

 

[Leesparkykent]

just to top the cylinder up once a week to 60 degrees or over to give the cylinder a cleanse. if the ASHP gets the water up to say 50 degrees the immersion isn't going to be running for long to get the hot water up to 60 degrees

 

[DiggerJ]

We have separate upstairs and downstairs HW cylinders - so lots of capacity. In the upstairs (bigger demand) we have the larger tank (162L) and we have fitted a pump to de-stratify the hot water; so using off-peak we get a full tank of Hot water, enough for all day usually.
My plan is in winter any tops if the ASWP doesn't fulfil need use oil fired boiler.
In summer use a short burst of off-peak.
I do a lot of monitoring of energy usage and this will help to optimise the various heat sources If/when I ever sell the house, it will take the buyer a long time to understand all the control strategies!

 

[snowhead]

If/when I ever sell the house, it will take the buyer a long time to understand all the control strategies!

Most home owners don't understand Thermostats, let alone Programable stats.
Your control Strategy has no chance.