Mating an air source heat pump with existing central heating DHW system

[Julian_P]

Hi to all, my first post. Sorry that this post will probably appear as one huge paragraph but for some reason or other my keyboard return key won't do anything on this forum :-( Anyway, I'm about to purchase said heat pump and having studied the wiring diagrams am getting my brain in a knot working out how to wire it up. The power supply is the easy bit with suitable cable and an isolator switch. This must always be live so that the HP can run the heating circulation pump if the outside temp drops lower than 7 degrees to keep the unit's heat exchanger from freezing up. I wish to switch the system via my existing time switch that controls my old (LPG) boiler and 'Y' plan installation. Now, the problem I have is that the wiring diagram only shows it coupled to an 'S' plan system where it gets triggered via the 'free volts' connections from the two motorised valves, The output from my three port motorised valve is, I think, a live for the boiler and pump so no good really. So I wonder how I arrange a 'free volts' switch output? And also with the existing system with the motorised valve, any attempt by the HP to run the circulation pump to prevent freezing will potentially also trigger my existing boiler due to the wiring. I'm a bit stuck here - any ideas? Cheers Julian.

 

[AWheating]

probably best to contact the manufacturer via there helpline and ask there advise on the best solution.

welcome to the forum.

 

[Julian_P]

Well the manufacturer is Chinese so that's no good, but the supplier is in the UK so it's certainly a thought! But I think I have the solution - I can get a proper mains relay with 240volt coil and now have a switched volts free output that I can use to trigger the HP - stick it in a nice little IP65 plastic box on the wall and job's a goodun. Now regarding the HP and it's function to run the heating circulation pump if it's ''off'' and senses the possibility of it freezing up then I could fit an additional pump in the circuit that would just sit there and who's only function would be to run if the HP detected freezing conditions in the night. Would that be a workable solution, after all a circulation pump is just an impeller so shouldn't impede the flow of water if it were not turning? Now all I have to do is find out why my return key won't work on the forum and I have to post everything as one long unwieldy paragraph, I suspect it's some sort of Windows compatibility issue unless anyone has the solution? Cheers Julian

 

[Julian_P]

OK sorted

I needed to turn on compatability view, must be an old forum software that doesn't work with the latest windows version!

Cheers Julian.

 

[Dotty]

Internet explorer doesn't like the forum.

 

[Ermintrude]

The relay is the best method but u need to configure controls slightly better, ashp delivered heat isn't going to be absorbed into a hot system. U need to prioritise ashp over boiler and also have a pipe stat so that the ashp cuts off when flow is 10% below its max delivery temp. Otherwise ur leckky meter will heat the house!

 

[Julian_P]

Well I was just planning to use the LPG boiler for back-up and perhaps the odd day when it's super cold. The CH is more of a background heat in our house as we have a coal fired open kitchen range in the room we use most, so I think it should be good. To be honest I doubt the HP I will probably buy will ever be powerful enough to flow to 10% of max delivery temp, but I take your point though and could fit pipe stat very easily.

As an aside I wondered if I could get rid of the LPG tank in the garden, with it's annual rental charge and just have 4 large propane bottles on the go with an auto switchover valve - given how little I plan to use the boiler I think it should be fine, especially when you consider that I can buy the large propane bottle gas for less than what Avanti charge for bulk LPG!

Julian.

 

[Reg Man]

Come across something similar in the past with 3 port valves, and as previously mentioned fit relays. Best option is modify the system to two port valves (S Plan). Its so much more flexible and straightforward.

 

[Ermintrude]

4 propane cylinders? Hope u don't get prolonged cold snap!!!!! If in countryside why not look at solid fuel boiler with a decent thermal store u can add more heat inputs as u go. Get dual coil. One for pressurised and one gravity?

 

[Julian_P]

The relay is the best method but u need to configure controls slightly better, ashp delivered heat isn't going to be absorbed into a hot system. U need to prioritise ashp over boiler and also have a pipe stat so that the ashp cuts off when flow is 10% below its max delivery temp. Otherwise ur leckky meter will heat the house!

I've been looking more at the HP specs, that is one of the parameters that you can programme into its brain when you set it up.

Julian.

 

[Julian_P]

Please delete mods, posted in error.

 

[Julian_P]

4 propane cylinders? Hope u don't get prolonged cold snap!!!!! If in countryside why not look at solid fuel boiler with a decent thermal store u can add more heat inputs as u go. Get dual coil. One for pressurised and one gravity?

I know, you're probably right. I'm just being tight and looking for the eaiest way out and I resent paying Avanti gas £100/year rental for an LPG tank. I'm not that worried about the cylinders as I have a van and trailer and the local gas place is just a few miles away from me. Also, as daft as it sounds, the cost per litre for the large propane bottles is less that Avanti currently want for bulk delivery!

Cheers Julian

 

[lame plumber]

just get the cyls delivered, you wont be insured to carry them in your van/trailer, if you dont believe me just ask your insurers, they might want to up your cover costs!!!!!!!!!

 

[Jimbob]

i would convert everything to s plan for starters, makes wiring a bit easier.

i would you your existing controls to feed an external stat (using the grey/orange that would of fed boiler/pump), then from the external stat i would send the heat/cool off to each 2 port on flow from boiler/heatpump. Then use each 2 port microswitch to switch boiler and heat pump. Then integrating frost protection into that should be a doddle in my opinion.

its difficult to explain, need a diagram really

 

[Julian_P]

Thanks Jimbob, that does indeed sound like an ideal solution but It would be a complete swine to do I'm afraid. At the moment my hot water tank is in the airing cupboard and just about blocks access to the pump, junction box and three way valve. Doing any form of work to that lot would be a complete nightmare as I think they built the airling cupboard after the plumber had done his work!

Never mind, I think I have the solution worked out, not ideal, but it should work well enough....

Julian

 

[Ermintrude]

When your pump or 3 port go down, re pipe it so that easily accessible and s plan.

 

[Dickie]

Bulk LPG can be bought from anyone & you can fill any bulk tank with any propane, it's an open market now.

It's always easier to operate a system like this on single zone valves, giving you much more freedom with controls.

 

[Gray0689]

Bulk LPG can be bought from anyone & you can fill any bulk tank with any propane, it's an open market now.

It's always easier to operate a system like this on single zone valves, giving you much more freedom with controls.

Not over here you can't
The supplier has to fill and maintain there own tank
And will not fill another one without this being done and would charge you for it

 

[Julian_P]

Bulk LPG can be bought from anyone & you can fill any bulk tank with any propane, it's an open market now.

.

Hah, you wish

Theoretically you are correct. In practice the bulk LPG supplier will want to see that you have the tank inspected and certificated IAW PSSR requirements (pressure vessel legislation requiring specialist inspection and periodic hydraulic testing) and that you have risk assessments for the property WRT leakage etc etc.

The top and bottom of it is the the suppliers have you by the short and curlies here - it's too onerous to consider having your own tank. One of the reasons why I'd fairly keen to do away with them!

Julian

 

[Dickie]

But whoever ownes the bulk tank should supply you with that paperwork & if they don't you tell them you'll report them to H&SE & Ofgas.

 

[Julian_P]

But whoever ownes the bulk tank should supply you with that paperwork & if they don't you tell them you'll report them to H&SE & Ofgas.

The bulk tank is owned by the supplier (Calor, Avanti or Flo Gas for example) only the tank's owner is allowed to fill it. When your contract is up you can change suppliers easily as the old supplier ''sells'' it to the new supplier (as required by the legislation) whearas in the old days it was a long winded process involving two seperate visits by HIAB equipped lorries and a fitter to transfer remaining gas and make and make the connectins etc.

That's all the change amounts to. If you want to own your own tank, ie buy one from ebay or a tank distributor, then you have a pile of paperwork and tasks to perform before any supplier will fill it. In short, forget it!

Julian

 

[Reg Man]

Oil's the answer then?

 

[Julian_P]

Oil's the answer then?

Well that rather depends on the question:smug:

In general terms, having had both in different properties then I would always go for oil.

But now as I'm fitting an air source heat pump, my LPG fired boiler will be almost redundant. I will still need LPG for the wife's cooker and as a back-up to the heat pump. Accordingly it simply is not worth the cost of an new oil boiler and tank. So large propane bottles are the answer as I no longer need to rent aa bulk tank. 47kg bottle at £60 delivered (just checked) and at about 92 litres a bottle is no more expensive than bulk gas.

Julian

 

[Reg Man]

I did not think ASHP was in the original question. Personally, I have an ASHP no oil or LPG and it works out cheaper to run.

 

[Julian_P]

I did not think ASHP was in the original question. Personally, I have an ASHP no oil or LPG and it works out cheaper to run.

Well that's interesting nevertheless. If my ASHP works well enough then I may just rip out the LPG boiler altogether, but I'm too chicken to do it right now. It's an old Ideal Mexico floor standing unit which has given a great many years faithful service but I understand that the gas valves are no longer available so when that goes it's end of story for it by the sounds of things.

Putting in a new (which has to be condensing) boiler these days would be shear folly as they are expensive, have a short life-span and cost more due to parts and labour due to their unreliability than you would ever save in a month of Sundays on reduced gas consumption :-( So if anything I'll install a small electric boiler to augment and act as back-up for the ASHP.

Julian.