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Air Source Heat Pump (ASHP)

Does what it says on the tin
GoSeigen
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Re: Air Source Heat Pump (ASHP)

#221714

Postby GoSeigen » May 15th, 2019, 9:22 am

Itsallaguess wrote:
I've had one of these Rondostat electronic TRV's installed for a number of years now, and I'm very happy with it -

https://www.amazon.co.uk/Homexpert-Heating-Controls-Electronic-HR20UK/dp/B007AQ71U4

They're £20 delivered, and it was a simple swap-out for the upper section of the previous TRV.

Rather poor reviews: 40% at two- or one-star level complaining of complete failure of the units within a year. Is the link definitely for your unit?


GS

Itsallaguess
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Re: Air Source Heat Pump (ASHP)

#221732

Postby Itsallaguess » May 15th, 2019, 9:53 am

GoSeigen wrote:
Itsallaguess wrote:
I've had one of these Rondostat electronic TRV's installed for a number of years now, and I'm very happy with it -

https://www.amazon.co.uk/Homexpert-Heating-Controls-Electronic-HR20UK/dp/B007AQ71U4

They're £20 delivered, and it was a simple swap-out for the upper section of the previous TRV.


Rather poor reviews: 40% at two- or one-star level complaining of complete failure of the units within a year. Is the link definitely for your unit?


Yes - I've had no issues at all with my Rondostat, and would recommend them.

I did look at some of the recent user-reviews, and it sounds like local environment issues (damp / condensation) might be playing a factor in some of the problems. I don't have any of those issues, and it's done it's job brilliantly for a number of years now.

Cheers,

Itsallaguess

malakoffee
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Re: Air Source Heat Pump (ASHP)

#445732

Postby malakoffee » September 27th, 2021, 8:07 pm

I'm reviving this topic because "PhaseThree" made specific mention of owning an air2water ASHP for space-heating only.

My bungalow (1930s) has about 85 sq metres of floor space and is pretty well insulated by retrofitting.

I was hoping to replace the condensing combi gas boiler with an air2water ASHP to do the space heating ONLY.

I use so little hot water that I don't want to lose space to a hot water tank and the maze of pipework that seems to be required.

I'll be upsizing some of the older radiators and using the newer ones as they are.

My indoor heat requirements are 14 C on the thermostat i.e. abnormally low.

Is a space-heating-only ASHP readily available ? I'm trying to avoid being misled by salespeople who are tied to certain brands/products.

DrFfybes
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Re: Air Source Heat Pump (ASHP)

#445996

Postby DrFfybes » September 28th, 2021, 4:34 pm

malakoffee wrote:
Is a space-heating-only ASHP readily available ? I'm trying to avoid being misled by salespeople who are tied to certain brands/products.


I thought all ASHPs were for room heating, as the output temp is insufficient to get a storage cylinder up to the WRAS required temp to combat Legionella? Effectively they're a low temp output boiler with low running costs.

Paul

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Re: Air Source Heat Pump (ASHP)

#446001

Postby richlist » September 28th, 2021, 4:38 pm

You can get an ASHP that delivers hot air (up to 30 deg C) for room heating.

PhaseThree

Re: Air Source Heat Pump (ASHP)

#446063

Postby PhaseThree » September 28th, 2021, 6:41 pm

All commercially available domestic ASHPs have adjustable flow temperature. In a typical installation "low" temperatures are used to supply the space heating system, with "hot" flow temperatures used for indirect domestic hot water (DHW) heating. A controller and change over valve are used to decide which mode the ASHP is operating in.

As noted above the "hot" temperature is usually too low to pasteurise the hot water system to destroy nasties such as legionella, The usual solution is to use an electrical emersion heater to heat the DHW storage tank to a legionella killing 60C once a month.

Additional note :- I looked long and hard to find a real world example of a case of someone contracting legionella from an unpasteurised DHW system, I found no such example. Other countries do not have this requirement and don't have people dying in the shower. It seems to be a theoretical risk only.

The issue with using an ASHP to heat to DHW temperatures is one of efficiency. ASHPs get less efficient with greater the temperature rises. There is also more chance of icing of the external heat exchanger with higher temperatures. This then requires additional electrical energy to defrost, further reducing efficiency- Hence my decision to use an ASHP for heating only.

So you can use an ASHP that will supply just your heating system, but you are unlikely to find one that just does this. It will have the ability to provide higher flow temperatures for DHW which can be ignored.

As richlist mentioned an Air-to-Air heat pump may be a better/other solution. Take a look at https://www.daikin.co.uk/en_gb/product- ... pumps.html. If appropriate they could let you get rid of your radiators altogether.

malakoffee
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Re: Air Source Heat Pump (ASHP)

#446105

Postby malakoffee » September 28th, 2021, 9:02 pm

Thanks for this,

I read John Cantor's book "Heat Pumps for Homes" ( 2nd edition ) a few months ago and was left with the impression that there might be additional gubbins in a heat pump to further increase the flow temperature for DHW ( and not just an immersion-type heater ).
I'll have to have a re-read about that.

But you lead me towards the Air-to-Air possibility . . . . . . . . . . . . . . very interesting !

I was thinking of doing something like this as an experiment or transitional arrangement : i.e. hang on to the Gas boiler as a belt'n'braces fallback in the short-medium term.

Thus i could risk the lower cost of a suitable air-conditioner unit(*) and see whether it evolves to become the main space heating device.

(*) Cheaper and less disruptive than fitting an Air-to-water ASHP . . . .

. ... even better if I get a solar PV system and get the summer cooling for free !

DrFfybes
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Re: Air Source Heat Pump (ASHP)

#446208

Postby DrFfybes » September 29th, 2021, 10:30 am

PhaseThree wrote:
Additional note :- I looked long and hard to find a real world example of a case of someone contracting legionella from an unpasteurised DHW system, I found no such example. Other countries do not have this requirement and don't have people dying in the shower. It seems to be a theoretical risk only.


Going slightly OT, I did wonder about this as I looked into it after someone scalded themselves at work and we wondered if the burns risk was higher. In the 1980s a neighbour was very ill contracting Legionella from an air con system (it was his job) and I suspect it was similar cases spurred someone charged with making the world safe to come up with the rules.

Paul

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Re: Air Source Heat Pump (ASHP)

#448388

Postby genou » October 6th, 2021, 7:57 pm

I'm trying to get my head round what is possible in my 1902 built 3 storey semi. We have cellars, so I don't see any role for UFH. We do have double glazing, and decent insulation in the roof space. Theoretically the cavities had blown insulation installed, but when we put in the DG it's either invisible or not there.

We have gas fired wet radiators driven by a Potterton Precision ( 30kW ), with the main circuit in 15mm with 10mm tails to the individual rads. The rads are all T21s. If I am right in thinking that a 30 year old T21 puts out the same, or less, than a modern T21, then looking at the output figures for current T33 rads I could go from T21s on a delta T of 50 to ( perhaps 100mm larger in height ) T33s on a delta T of 30 with no loss of available wattage, and just hook in to the existing pipework. The current T21s are perfectly capable of keeping the house at T-shirt temperatures. Current gas consumption ( which includes cooking and hot water ) is 28k.

What I haven't got my head round is whether I can get enough flow through this pipe work, and what the relationship is between power output on a traditional on'/off system and power output on a trickle feed heat pump system.

Any comments welcome, and any pointers as to what I should be reading gratefully received.

88V8
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Re: Air Source Heat Pump (ASHP)

#448495

Postby 88V8 » October 7th, 2021, 11:07 am

genou wrote:We have gas fired wet radiators driven by a Potterton Precision ( 30kW ), with the main circuit in 15mm with 10mm tails to the individual rads.
What I haven't got my head round is whether I can get enough flow through this pipe work, and what the relationship is between power output on a traditional on'/off system and power output on a trickle feed heat pump system.

Hmmm. 10mm. Penny pinching. Microbore was a thing once, years ago, then it wasn't. Too much small pipe makes the system noisy, and large rads simply cannot get enough flow to reach their rated output.
In a well-designed GFCH system the main circuit should be 28mm at the boiler where it is running HW and CH, then the CH should be at least 22mm with 15mm branches. No or very little 10mm. At least you have no 8mm.

Heat pumps typically need higher flow rates due to the lower temp on flow and return. You may get flow alarms on the ASHP if there isn't enough flow for it to deliver the required system output. Some ASHP installations even require a 28/35mm backbone as normal 22mm pipework means a significant rise in system velocity to meet demand and therefore create more system noise.

You will also need larger rads. Perhaps double the output. More wall space. This can be mitigated by using cast-iron rads, which have a higher output for a given wall space, and also suit a Period house.
As recommended here https://www.isoenergy.co.uk/more-information/radiator-sizing-for-heat-pumps

Before you go any further I would get a couple of specialist installers in and see whether they will guarantee the results with your existing pipework.
At the very very least, if you find the largest rads don't get hot enough you may need to remove some of the 10mm and go up to 15mm. That of course creates balance issues, but should not be insuperable.

As regards overall output, the system has to replace the heat lost by the house, so the overall requirement does not change. The reason the heat pump is often run 24/7 is that it does not have the extra oomph needed to raise the temperature rapidly, as you can do with a gas system.

Make sure your installer is well versed in setting up these systems to ensure you have a trouble free installation.

V8

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Re: Air Source Heat Pump (ASHP)

#451236

Postby Watis » October 19th, 2021, 10:58 am

Found this article in the Guardian where ASHP owners were asked for their opinions on the systems they had bought.

Some are for, others against. What differentiates them appears to be the word 'Mitsubishi'.

https://www.theguardian.com/money/2021/ ... ng-outside

HTH,

Watis

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Re: Air Source Heat Pump (ASHP)

#451239

Postby Mike4 » October 19th, 2021, 11:06 am

Watis wrote:Found this article in the Guardian where ASHP owners were asked for their opinions on the systems they had bought.

Some are for, others against. What differentiates them appears to be the word 'Mitsubishi'.

https://www.theguardian.com/money/2021/ ... ng-outside

HTH,

Watis


I'm inclined to point out that a Mitsubishi, incorrectly specified and installed will be just as disappointing as any other heat pump. And given the price of them combined with the average UK consumer's tendency to pick the cheapest quote rather than look into why the higher quotes are higher, there is enormous pressure on installers to quote for undersized, smaller and cheaper heat pumps.

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Re: Air Source Heat Pump (ASHP)

#451241

Postby Watis » October 19th, 2021, 11:10 am

And here's another article, this time from the BBC, no doubt triggered by the Government's announcement of £5,000 grants.

https://www.bbc.co.uk/news/science-environment-57159056

Watis

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Re: Air Source Heat Pump (ASHP)

#451246

Postby scotview » October 19th, 2021, 11:26 am

It seems to me that heat pumps need extremely high specifications of insulation to maximise their benefits, including retro-fit. Particularly for winter running.

If a home were to be retro fitted to these very high spec insulation levels, would electric panel heaters not be as equally effective and have the advantage of having selective heating in different rooms rather than running continuously. Possibly less install disruption also.

Does anyone know of any studies comparing insulation thermal effectiveness v panel heaters v heat pumps.

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Re: Air Source Heat Pump (ASHP)

#451273

Postby richlist » October 19th, 2021, 12:55 pm

There is a lot of discussion about wet systems. What about the hot air systems available with ASHP's ? We have one of these in Spain where they traditionally don't install any insulation in new build property. It works very well......would work considerably better in a fully insulated property.

I'd probably need 2 or 3 larger units to cover my detached place then I could do away with radiators completely.

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Re: Air Source Heat Pump (ASHP)

#451284

Postby bungeejumper » October 19th, 2021, 1:32 pm

richlist wrote:There is a lot of discussion about wet systems. What about the hot air systems available with ASHP's ? We have one of these in Spain where they traditionally don't install any insulation in new build property.

Aaaah, that takes me back a bit. My parents had ducted warm air in their 1960s newbuild, and so did everyone else on their housing development. First problem was that it was really very expensive to run. Second problem was that it was a torment to anyone with a dust or pollen allergy. (I imagine pollen filters are standard these days?)

The third problem took a little longer to appear. Rats and mice enjoyed the warm underfloor environment so much that they stayed around the galvanised ducting until they eventually died. And then they cooked gently, and the wafting aroma got into every room. Within three years, everyone on the estate had switched back to wet systems with radiators. LOL, I imagine the dead, draughty ducting is still down there? :lol:

BJ

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Re: Air Source Heat Pump (ASHP)

#451285

Postby richlist » October 19th, 2021, 1:33 pm

Wet systems use hot radiators to heat the surrounding air.......air to air systems just blow hot air into the room without the need for water. They can be run in reverse to provide air conditioning in the summer. Ok, they aren't suitable for all properties but there isn't a one size fits all for anything in life.

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Re: Air Source Heat Pump (ASHP)

#451323

Postby UncleEbenezer » October 19th, 2021, 3:27 pm

scotview wrote:It seems to me that heat pumps need extremely high specifications of insulation to maximise their benefits, including retro-fit. Particularly for winter running.

If a home were to be retro fitted to these very high spec insulation levels, would electric panel heaters not be as equally effective and have the advantage of having selective heating in different rooms rather than running continuously. Possibly less install disruption also.

Does anyone know of any studies comparing insulation thermal effectiveness v panel heaters v heat pumps.


The advantage of the heat pump is that the power in drives a pump, not a heater. It gets several times more heat out per unit energy consumed than any heater.

The balance of that with other considerations is above my pay grade.

Not every house can take an air-source heat pump: mine can't, for one. I wanted a river-sourced heat pump (much more efficient: water has four times the specific heat of air), but got overtaken by circumstances.

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Re: Air Source Heat Pump (ASHP)

#451353

Postby DrFfybes » October 19th, 2021, 4:54 pm

richlist wrote:There is a lot of discussion about wet systems. What about the hot air systems available with ASHP's ? We have one of these in Spain where they traditionally don't install any insulation in new build property. It works very well......would work considerably better in a fully insulated property.

I'd probably need 2 or 3 larger units to cover my detached place then I could do away with radiators completely.


We would have to do that. The 2 companies we had both said we didn't have enough wall space to house the radiators we'd need unless we clad or intenally insulated, and replaced the roof with a one with more than 22 inches of headroom at the apex so it could be insulated. a rough figure was £18k for a system of sufficient capacity, against £5k for a boiler 40 years newer than the current one. You can buy a lot of gas for £13k :)

Paul

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Re: Air Source Heat Pump (ASHP)

#451570

Postby 88V8 » October 20th, 2021, 11:36 am

DrFfybes wrote:The 2 companies we had both said we didn't have enough wall space to house the radiators we'd need unless we clad or intenally insulated, and replaced the roof with a one with more than 22 inches of headroom at the apex so it could be insulated.

Good that they didn't try to sell you something that won't work.
ASHPs have the potential to be another 'mis-selling scandal' after a few cold winters.

V8


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