ASHP

[nod]

I’m preparing the sap and need to decide on  heating 

I would have preferred ASHP on our first build But was over ruled due to there being gas right outside No gas on our next builds 

Easy decision No My wife thinks a oil fired boiler would be good 

A couple of builds nearby have been passed using oil boilers God knows how 

Just feels like a step backwards to me 

 

My question is Is there any RHI incentives out there Reading one of the build mags they seem to be changing things in March 

 

 

[crispy_wafer]

Just now, nod said:

My question is Is there any RHI incentives out there Reading one of the build mags they seem to be changing things in March 

 

 

 

Here's hoping they put something in place for after next March, I'm all set on ASHP, but no way will I be done in time to submit RHI.

[IanR]

Yep, needs to be commissioned before 31.03.2022 as RHI is stopping.

 

No word on whether they'll be anything to replace it, but they plan to encourage more new builds to go with heat pumps from 2022, so there maybe incentives.

[nod]

Thanks

Watch this space then ?

[ProDave]

Just buy one and fit it yourself.

 

If you are not paying an MCS registered company to install it, you might find it is nowhere near as expensive as you think.

[joe90]

9 minutes ago, ProDave said:

Just buy one and fit it yourself.

That’s what I did far cheaper than thro RHI.

[dpmiller]

^ wot they said.

[SteamyTea]

The whole idea of the RHI and the FiT was to encourage business to install the stuff.  Once the installation knowledge base was there, the MCS companies should be more expensive.  Why the governments (both flavours) thought it was a good idea to pay customers, rather than pay companies I don't know, but that is the route that was taken.

People moan that they can only get 5p/kWh for exporting electricity, but I think that is pretty generous, I pay nearly 11p to import it at night, and 23p/kWh during the day.

Yesterday, if I had a 4 kW_p system, I would have generated about 22 kWh, I only used 6 kWh, so my imports cost about 80p, but I could have got £1.10 for exporting.  And that is without self consumption.  If I could use half of my consumption, 40p worth, and exported the rest (16 kWh), I would have been 40p up.

I wish I had a large enough roof to fit 4 kW_p and it was pointing in the right direction.

[crispy_wafer]

11 hours ago, ProDave said:

Just buy one and fit it yourself.

 

If you are not paying an MCS registered company to install it, you might find it is nowhere near as expensive as you think.

 

11 hours ago, joe90 said:

That’s what I did far cheaper than thro RHI.

 

2 hours ago, dpmiller said:

^ wot they said.

 

Yes, this could be the answer, the fear of breaking something though is strong...

 

I've been quoted £7890 to install a Panasonic MDC09J3E5 a quick google suggests this can be had for 2800'ish before VAT, so 5k for signing a bit of paper.  Sat in the office, part of me is saying 'yeah, I could do this myself, and save a wedge that could be put to good use elsewhere in the build'.  The other half says, 'you haven't got a clue, leave it to the experts, unless you want to be sat in the floor/garden surrounded by bits'.

 

[LA3222]

Buy a pre plumbed cylinder.and most of the work is done for you!

[PeterW]

There is very little to do on an ASHP. It’s two pipes, a power connection and whatever controller they need for the device. Most have some sort of dedicated control unit that then has a single control cable running from that into the ASHP. 
 

I would say it’s no worse than installing a boiler and there is no gas to worry about ..!!

[SteamyTea]

2 hours ago, crispy_wafer said:

I've been quoted £7890 to install a Panasonic MDC09J3E5 a quick google suggests this can be had for 2800'ish before VAT, so 5k for signing a bit of paper.  Sat in the office, part of me is saying 'yeah, I could do this myself, and save a wedge

Just get a plumber to fit it, just show them what needs to be done. They are not going to charge much if you have got the unit in place, cables run and holes drilled for any pipes.

Why pay a plumbers rate, and an hour of his time, to carry a cylinder upstairs.

Edited July 9, 2021 by SteamyTea

[SimonD]

ASHP isn't just about chucking in the pump and cylinder though is it? You've also got to design and commision the whole system so that it all functions correctly. I know someone who paid a lot of money for a heatpump installation and because something was wrong, it's burned through 3 compressors and now requires a whole new heatpump as replacement.

[markocosic]

1) Insulate and airtight

 

 

2) Space heat easy:

 

- Design for a maximum space heating flow temperature for 45C at design condition (rad size) or ideally 35C (UFH)

- Design for a 5C deltaT across emitters rather than 20C (presettable TRV body selection to get correct flowrates at full output)

- Design with open zone where possible (usually downstairs open plan one zone, and the only TRV heads fitted upstairs)

 

 

3) Hot water can be good/easy or ok/cheap but not both:

 

- Ideally buy a packaged system (ASHP and cylinder from the same OEM)

- RTFM for how the device charges a cylinder (how does it decide when it is satisfied)

- Pick a cylinder with a large coil if using a cheapo Asian monobloc ASHP that isn't designed for hot water production

- Use a larger tank and limit DHW storage temperature to 45-48C

 

 

The "correct" way to control hot water with little heat pumps is based on pressure in the refrigerant circuit (you keep on running until you trip a "high pressure" threshold, achieving the max possible temperature within compressor/refrigerant limits, rather than running well below the max in order to avoid burning up the compressor - and you use a scroll compressor with vapour injection rather than a rotary) and the "correct" way to generate it by running the space heat and hot water at the same time; generating the (higher temperature) hot water via a desuperheater and the (lower temperature) space heating via the regular condenser. That's more gubbins than you'd like to pay for so the midrange units tend to eliminate the desuperheater, then then the pressure control, then the scroll compressor.

 

 

In mild climates and for low demands you can get away with rotaries. For harsh climates and high demands scrolls all the way. (CTC, Nibe, Danfoss, some Daikin etc)

 

[SimonD]

1 hour ago, markocosic said:

you keep on running until you trip a "high pressure" threshold, achieving the max possible temperature within compressor/refrigerant limit

 

A recent discussion with a Swedish heat pump manufacturer re the problem I mentioned above, said that compressor should not be regularly tripping out at the high pressure threshold as that indicates a problem within the system and will cause excess wear on the compressor system (this what was happening in the example I mentioned, hence premature wear of three compressors). Admittedly this is on a geothermal heatpump rather than air source, so may be a diffierent issue. Now, I can only take their word for it as I'm no expert at this kind of thing so very happy to understand more.

Edited July 10, 2021 by SimonD

[markocosic]

Exactly that. You should be anywhere near the high pressure limit. 

 

 

You could:

 

Run up to a "working pressure limit" and the stored hot water temperature in the ta is "whatever it can get to, or 95C, whichever occurs first"

 

If working without the desuperheater a typical "working pressure limit" is a water temperature of 50-55C on R407C/R410A if you have a good (low input <> tank deltaT) tank (I haven't looked for R32 but imagine that it's similar). If you've got a desuperheater and a large space heat load relative to hot water load then you might top out at 95C on the stored hot water unless dialled back artificially.

 

 

Or you could:

 

Run up to a "tank temperature" limit (without having a clue what the refrigerant is doing) and hope that you don't jack the refrigerant pressures through the roof in the process.

 

Setting a 45C tank temperature in a mild climate with a large coil (so low coil<>tank deltaT) is going to be fine. Aiming for 60C tank temperature (on R407C/R410A - haven't looked for R32 but imagine that it's similar) will cook things. Aiming for 50-55C tank temperature with a small coil (so high coil<>tank deltaT) or low source temperature and no EVI is risking cooking things. Cheap temperature sensors (bimetallic strips) can be horribly inaccurate / have high hysteresis too. 

 

 

 

Space heat is difficult to get wrong unless doing something seriously / obviously dumb like running it at a high temperature. Hot water is trickier because you do need to run up to the limits of what the refrigerants and compressors can do. Your safe bet is buying the heat pump and hot water tank as a package engineered to work together by (a) people with a clue and (b) people who will warrant the package. (including the COP)

 

Your riskier bet is buying the heat pump from Brand X, a cylinder and associated widgetry from Brand Y, and taking the engineering risk of putting them all together and operating the heat pump within it's operating range for long life. (and it'll be you the client not Phoenix Ltd the installer or local distributor that take the risk) You can do this but be careful. Tank with good heat exchange. Good temperature sensor (ideally one from the heat pump stuck into a dedicated sensor pocket in the right place on the tank not a 3rd party strap on guess-o-meter). Safe setpoint (45-48C). Should work fine.

 

 

Beware the small print.

 

 

Freedom (one of the better distributors IMO) advertise the Samsung as delivering up to 60C temperatures down to -2C. That's kinda ok, but to be honest I'd be more interested in -7C or -10C for a UK installation as that's going to dictate how large your radiators should be. (hence advice to design for 45C or below). Other distributors or idiot installers will advertise it as capable of 65C which yeah, it could do if it's hot outside, but this is irrelevant.

 

 

Dig into the manual and there's a remote sensor with the heat pump (so it isn't trusting a 3rd party sensor to be right) for the DHW and they're advocating a 48C setpoint (perfect) whereas other distributors or idiot installers might say "Oh, but it can do 60C or 65C and try to set the tank to that and watch the compressor die (unless it self protects - I'm not familiar with these but chose it as the first brand name example I found)

 

https://f38ad20b-7d4c-44f2-9ac3-94ddf2ca9af9.filesusr.com/ugd/40079d_271454ec92a740a1894b806a48ff5800.pdf

 

 

R134a does go hotter. You shouldn't need it in a domestic application. Some vendors use it for simpler heat pumps designed for "robust yet meh" performance in retrofit applications.

 

 

Personally I think the future for low demand houses is going to be separates...but going full separate rather than trying to bodge a heat pump onto a tank "by other" - e.g.

 

Air to air heat pump for space heat / cooling. Air to water heat pump cylinder (from $999.99 at big box DIY stores in the USA and idiot simple to...plug in) for taking heat from the house and making hot water.

 

Such cylinders are still expensive in the UK but coming down as volume becomes more than zero:

https://www.dimplex.co.uk/product/edel-hot-water-heat-pump

https://www.electricpoint.com/dimplex-edel-hot-water-cylinder-heat-pump-200l-edl200uk-630rf.html

 

Or better yet:

 

Air to water heat pump for space heat / cooling. (heated / chilled UFH and towel rail) Water to water heat pump cylinder for hot water. These are nicer IMO as the the cylinder chills your slab in summer and you "top up" the slab from A N Other source in winter as required. These with a basic monobloc whose only job is to (directly) serve the slab (control strategy can be as simple as "run a weather compensated loop and keep the return above 21C" will work nicely.

 

https://www.auer.fr/en/products/heat-pump-water-heaters/edel-water-heat-pump-water-heater/

 

 

Which is why I'm about to chuck in a state-of-the-ark fixed speed ground source unit with a built in tank (Danfoss DHP-H 6; a rebaged Thermia) myself. ? (it was £600 with 1,000 run hours on it, we have loads of space, and I can get a pipe/digger cheap)

 

Else I'd be seriously considering a totally standalone DHW tank with built in heat pump to cool the house in summer; plus topup heating/cooling from an air source monobloc. Backup would be a 2 kW fan heater or wood fired hot water tank if out in the proper sticks!

 

e.g.

https://online.depo-diy.lt/productItem/27620/7154

[ProDave]

6 hours ago, SimonD said:

 

A recent discussion with a Swedish heat pump manufacturer re the problem I mentioned above, said that compressor should not be regularly tripping out at the high pressure threshold as that indicates a problem within the system and will cause excess wear on the compressor system (this what was happening in the example I mentioned, hence premature wear of three compressors). Admittedly this is on a geothermal heatpump rather than air source, so may be a diffierent issue. Now, I can only take their word for it as I'm no expert at this kind of thing so very happy to understand more.

That to me sounds like the water flow rate is not adequate and not taking heat away from the ASHP quick enough so it is getting too hot.

 

Most ASHP's now have a water flow switch and will flag an error and shut down if the water flow rate is inadequate.

 

I only encountered this issue once when setting up a GSHP and it kept throwing a high pressure error and that was the reason.  It took a modification to the plumbing to improve the water flow rate to solve it.

 

 

[dpmiller]

Our inverter ASHP (with Carel control gear and inverter unit) is pre-programmed with all the settings for various different compressors. Loadsa numbers for electrical, pressure, and temperature characteristics. Not a pressure switch to be seen, everything on sensors.

[SimonD]

13 hours ago, ProDave said:

That to me sounds like the water flow rate is not adequate and not taking heat away from the ASHP quick enough so it is getting too hot.

 

I only encountered this issue once when setting up a GSHP and it kept throwing a high pressure error and that was the reason.  It took a modification to the plumbing to improve the water flow rate to solve it.

 

 

 

Thanks, that's helpful. Unfortunately, I can't go and test right now as I'm here in England and the heat pump is in my mother's house in Sweden. Unfortunately the installer seems pretty rubbish and is fobbing her off while the manufacturer has been pretty good. Manufacturer is having a word with installer.... I think that one major problem is they've focussed only on the heat pump, not looking at the whole system.