Small ASHPs / Units primarily for DHW

The Mitsi unit linked above looks fun. It really comes to life when producing HOT water with a LARGE temperature rise. (CO2 heat pumps best at say 60/30C)

https://refrigerationcomponents.co.uk/ecodan-4kw-monobloc-air-source-heat-pump-with-thermal-stove-quhz-w40va.html

Can they do cooling?

If hot water temperatures are more modest a basic R290 unit will do almost as well.

Beelbeebub · July 20, 2023

From my reading of the specs, the r744 (CO2) unit really only comes into its own providing high temp (65+) water from cold mains, as @markocosicsays, they are different from normal heatpumps in that the COP is very dependent on the return temp being low. I.e. they work more efficiently providing a flow of 75 from a return of 20 than if the return was 55 - wierd I know.

So the advantage is you can create a store of very hot water, which means you can have a smaller cylinder. I guess that's why they are popular in Japan.

If you don't need blisteringly hot water and might need some heat, a r32 (split or monoblock) or r290 (monoblock only) heatpump is probably better. The cops are similar but it's less "exotic" tech from more suppliers.

Oh and the other option for air to air would be a multi split, one outside unit and 2 or more inside.

Daikin do a system where one of the inside units can be a (specially designed) hot water cylinder.

T M · July 21, 2023

21 hours ago, markocosic said:

Nice one @T M

It's not obvious what one ought to do in a modest home.

Thanks for the info @markocosic.

Yes indeed it is not very obvious which one to choose, which is why I wanted to post some of my findings about the ventilation heat pump to help inform others what I found.

To respond to your comment above: each house has a unique set of parameters that needs careful consideration.

1) Small, Medium or large house

2) DHW demand High or Low

3) Climate cold, mild or hot

4) Existing build or new build

5) Well insulated or not

6) existing radiators (high temp) or floor heating (low temp) or ducted system (air)

7) Local installers preference, parts, maintencane & service (the more common the cheaper it will be to maintain)

8) Budget and operating cost targets.

9) Ground source option, Split outdoor units possible, or no outdoor unit possible.

10) Personal comfort: floor heating, airconditioning, radiators,

In my case we are building a new, small, highly insulated house in a mild climate with a low DHW demand, good Vaillant and Mitsubishi service and have an option to have an outdoor unit.

So that narrows it down to basically three options:

Air to Air (no outdoor unit)

Air to Air (outdoor unit)

Air to water (Split)

Here is a general estimate of the cost and comfort of the three options:

1) Air to Air ventilation (Genvex Combi 185 or similar) €8000 + installation €2000 is also the balanced ventialtion system. Operating costs €1700/yr comfort 5/10 Cost after 10 years = €27000

2) Air to Air split (Mitsubishi multisplit) €2500 + installation €2000 + balanced ventilation €1500 + Water heater €1000+ Operating cost €900/yr comfort 7/10 Cost after 10 years = €16000

3) Air to Water split (Ecodan or Arotherm) €8000 + installation €2000 + floor heating €4000 + balanced ventilation €1500 + Operating cost €600/yr comfort 9/10 Cost after 10 years = €21500

So conclustion:

If you are on a budget and value having airco more than floor heating go for option 2.

If you want more winter comfort, DHW and quiet, with less summer cooling comfort go for option 3.

Edited July 21, 2023 by T M

T M · July 21, 2023

19 hours ago, Beelbeebub said:

From my reading of the specs, the r744 (CO2) unit really only comes into its own providing high temp (65+) water from cold mains, as @markocosicsays, they are different from normal heatpumps in that the COP is very dependent on the return temp being low. I.e. they work more efficiently providing a flow of 75 from a return of 20 than if the return was 55 - wierd I know.

So the advantage is you can create a store of very hot water, which means you can have a smaller cylinder. I guess that's why they are popular in Japan.

Thanks @Beelbeebub for you elaboration of the difference between the technology of the Ecodan and the Arotherm.

Yes indeed the Ecodan is more exotic and operates at about 20degrees higher so would be ideal for a traditinal high temperature radiator retrofit or if you want a smaller indoor unit and more DHW:

Ecodan 200L 1600x595x680mm Arotherm 190L 1880x599x693mm

I was more trying to get a grasp on categorizing the different types of heatpumps (air-air, air-water, and water-water) categories and costs.

To me I see the Ecodan and the Arotherm split heat pumps in the same family (air-water) with a specialization in high or low temperature heating output.

Both are very efficient and get good reviews and depending on the heating system and installer preference could be a wise choice.

T M · July 21, 2023

21 hours ago, markocosic said:

The Mitsi unit linked above looks fun. It really comes to life when producing HOT water with a LARGE temperature rise. (CO2 heat pumps best at say 60/30C)

https://refrigerationcomponents.co.uk/ecodan-4kw-monobloc-air-source-heat-pump-with-thermal-stove-quhz-w40va.html

Can they do cooling?

Yes the Ecodan can also run in reverse and cool water to a temperature of 5°c

But if you have floor heating with hardwood floors there are issues with condensation (mold) so is most safe if you have a concrete floor.

The cooling function does not work that great with radiators but helps a bit.

The mini-split is better at cooling and also dehumidifying, and can also heat in the winter so if cooling is important then a mini split might be a better option.

markocosic · July 21, 2023

33 minutes ago, T M said:

the Ecodan is more exotic and operates at about 20degrees higher so would be ideal for a traditinal high temperature radiator retrofit

Nope.

It's useless for this.

You need to be returning at below 30C for CO2 to shine as a refrigerant.

Radiators at e.g. 60/30C will have a similar output to radiators at 48/42C. A propane heat pump at 48/42C would have better performance here.

It's good for a main dish ofnhot water production with a side salad of heating/cooling.

JamesPa · July 21, 2023

On 29/07/2019 at 13:11, joth said:

oh yes, thank you for this. Yes that's the distinction - this one does say the installation needs to comply with the MCS planning standards, not that it needs to have been done by an MCS certified installer.

The standard mostly seem to be measuring and documenting the compliance with noise limits.

If you read the source documents , ie the actual legislation and the 'MCS Planning Standards' to which the legislation refers, I'm personally 100% convinced that MCS is required for PD. MCS seem to have caused this to happen because it's a consequence of the way the 'MCS Planning Standards' are written. I'm used to finding loopholes in regulations but in this case I can't find one that I am convinced by.

I have challenged MCS on the immorality of creating a closed shop by the backdoor in this way; they don't deny it is the effect of the documents, but claim that others were responsible for this effect - the 'it's not my fault gov' defence which is only one step removed from, or possibly equivalent to, the Nuremberg defence.

T M · July 21, 2023

13 minutes ago, markocosic said:

It's good for a main dish ofnhot water production with a side salad of heating/cooling.

Okay good to know! Thanks.

In my case we have a really low DHW demand so I guess the Vailliant Arotherm like my advisor suggested would make the most sense.

Edited July 21, 2023 by T M

Beelbeebub · July 21, 2023

The CO2 unit's efficency is critically dependent on the return temp as mentioned.

For heating the return temp is typically too high, say 35, 45C and the efficency crashes

It might just work with a fan coil or UFH *if* you could get the return down to 22C or so.

With a DHW the "return temp" is whatever the local water supply is, typically well below 20C, maybe even 10C in winter.

The CO2 manual says it's critical to hear the cylinder in a stratified fashion, so you always have a very cold base to cool the return right down. If you try and run it like a typical heat pump it is very inefficient.

Beelbeebub · July 21, 2023

Oh and I would second not bothering with a wood stove. I have very well insulated house. (8" wool insulation, high speed windows, air tight etc).

To be fair one IKEA bag of wood does heating and hot water for 24h and I have access to free wood.

And there is something nice about a.fire on a cold winter's night.

But.....

We can only use our small 4kw to room, 6kw to water stove once a day if it is near or below zero. Otherwise we overheat.

We run the stove a few dozen times a year.

If the wind is in the wrong direction we can't run it because the plume goes towards the MHRV intake.....😱

The dust from loading/unloading is a pain.

As is storing the wood and lugging it in and out.

If I was building again, I wouldn't bother.

JohnMo · July 21, 2023

We put a stove in, we don't use it often, and does take a while to get used to using in well insulated house. One big log or a couple of smaller ones on min air sees us with enough heat for the night. We got a soap stone stove to slow the heat release, which it does. The stove is rated at 4 or 5kW but I think the lowest output is around 1 to 2kW. We use so little wood and it burns so well that the ash bucket got emptied once last winter.

Iceverge · July 21, 2023

On 20/07/2023 at 16:42, T M said:

After a heat loss calculation was made by a professional it was determined the annual heat consumption would be approximately 5280kWh/year

Heat transmission loss: 28W/m2 Ventilation loss: 16W/m2 Absorption loss: 14W/m2

I think your professional has wildly over estimated the heat loss.

That is almost 6 times passivhaus levels and you have near passivhaus insulation.

Have you tried consulting the heat loss spreadsheet on here to see if your predicted losses are that high?

Iceverge · July 21, 2023

7 minutes ago, Iceverge said:

I think your professional has wildly over estimated the heat loss.

That is almost 6 times passivhaus levels and you have near passivhaus insulation.

Have you tried consulting the heat loss spreadsheet on here to see if your predicted losses are that high?

Also what is your predicted electric price for 10 years?

If you have an option of cheap overnight electricity it may be better not to install any heat pump but just enjoy the low capital outlay and trouble free operation of an immersion and a few storage heaters.

For info 186m2 in the south of Ireland we use about 3200kWh for space heating and 3650kWh for a family of 4. Passive insulation levels.

T M · July 22, 2023

10 hours ago, Iceverge said:

I think your professional has wildly over estimated the heat loss.

That is almost 6 times passivhaus levels and you have near passivhaus insulation.

Have you tried consulting the heat loss spreadsheet on here to see if your predicted losses are that high?

Yes that is what I thought too.

So I had another company also do the heat loss calculation and they came to a very similar result.

There is a very specific methodology in the Netherland that all professionals follow to make an official heat loss calculation report.

I asked about this and he said they need to assume all the worst case scenario of a very cold winter with extended temperatures of -10 degrees which almost never happens, but theoretically could happen.

The professional I hired did the calculation for the ventilation heat pump which he said uses more energy because it has to continuously heat up large volumes of outdoor air so he added +16W/m2 for ventilation loss. The true heat loss is about 28W/m2 (in extreme conditions) the Absorption loss is a safety factor they also use here.

But it is comforting to hear that your home is over double the size and uses less energy than we have modelled.

If we used a split heat pump with balanced ventilation (with a heat exchanger) we can cut the ventilation loss out and if we take the safety factor out then the actual energy consumption will be more in the range of 2600kW/yr for space heating in an extreme winter and probably in a normal year the space heating demand will be more like your house using about 18-20W/m2

T M · July 22, 2023

10 hours ago, Iceverge said:

Also what is your predicted electric price for 10 years?

If you have an option of cheap overnight electricity it may be better not to install any heat pump but just enjoy the low capital outlay and trouble free operation of an immersion and a few storage heaters.

For info 186m2 in the south of Ireland we use about 3200kWh for space heating and 3650kWh for a family of 4. Passive insulation levels.

The average price for electricity in the Netherlands is around 50cents /kWh

Some electricity providers have off peak rates that are between 10-40cent/kWh

That could also be an interesting solution to use an immersion heater and buffer tank (like a battery) and charge it with low tarrif electricity and solar energy.

This would have a simiar operating cost as a split heat pump and much less upfront investment cost.

Very interesting idea, thank you!

I will investigate!

Nic · February 25

Hi

just discovered this post and more confused on what to consider for our future build

will be built to passive air tight standards. Will only be 55m2 downstairs and two double en-suites upstairs . 1 bath 1 with shower . So total is 110m2

downstairs is all open with a small utility room where I have about 24m ceiling and about 1 meter square of space. This is for however I’m going to do MVHR, DHW , one zone UFH .As you can see was looking at a one box solution like the Genvex combo or PKOM 4. I can obviously put an ASHP outside and a compact MVHR. But still need cylinder …… please help 🙏

markocosic · February 26

I would:

- Monobloc ashp outside (something like a 5 kw vaillant unit)

- Ufh downstairs (direct fed from diverter valve)

- Heated/cooled ceilings upstairs and downstairs (chilled by ashp in summer; heated slightly in winter; changeover can be a manual valve moved seasonally to disable the ufh

- Regular hot water cylinder (direct fed from diverter valve) separate from the mvhr above it

- Wastewater heat recovery (1/3 or more off your shower cost and extends runtime of the cylinder of a given size)

JohnMo · February 26

7 hours ago, markocosic said:

Heated/cooled ceilings upstairs and downstairs (chilled by ashp in summer; heated slightly in winter;

Why the added complications, UFH is fine on its own for heating. Can do cooling also, just flow at 15 degrees, will knock the extremes of summer heat off and cost next to nothing to do.

Everything else sounds good.

Gone West · February 26

12 hours ago, Nic said:

Genvex combo

If you mean a Genvex Combi 185 then the DHW tank is 185 litres and it's space heating output is warm air, not hot water for UFH. If the house is insulated to significantly better than PH maximum standards, ie U factors of no more than 0.1 W/m2K then the Genvex Combi 185 LS version should be sufficient for a house of that size.

Nic · February 26

42 minutes ago, JohnMo said:

Why the added complications, UFH is fine on its own for heating. Can do cooling also, just flow at 15 degrees, will knock the extremes of summer heat off and cost next to nothing to do.

Everything else sounds good.

thanks

so are we saying an ASHP to run UFH and DHW then just the MVHR to do air changes ( plus a little bit of heat via the warmed air? )

recommendations of units would be most welcome . Also is the zehnder q350 my best option for a small MHVR ? Is there likely to then add small ( squat) cylinder under it? Are there such things? What else would I need on inside if ASHP on the outside? Sorry to ask so many question's, is valiant 5kw able to run DHW and UFH at same time or is it a case of it automatically switching from one to the other when asked ?
thanks again

sharpener · February 26

1 hour ago, Nic said:

is valiant 5kw able to run DHW and UFH at same time or is it a case of it automatically switching from one to the other when asked ?

Natively it does HW priority (like most other HPs) which de-powers all heating circuit valves. There is a Parallel Cylinder Charging mode which you can engage if you particularly want to do both at the same time. But why would you?

IMO best time to heat the water is in the small hours on cheap tariff, this utilises the stored water for timeshifting and interferes minimally with heating. Top up in the afternoon if reqd as the OAT is typically higher then so you get slightly better CoP.

JohnMo · February 26

1 hour ago, Nic said:

plus a little bit of heat via the warmed air?

Really zero need, UFH can do all the heating you need. If you have a thick screed, circa 100mm you can charge the floor like a storage heater on mostly cheap rate (E7 or similar). This takes a hit on CoP, but the electric is cheap.

You can get cylinders in just about any shape you want, or get it made to the size that suits you. Get one with a 3m2 coil.

Nic · February 26

8 hours ago, JohnMo said:

Really zero need, UFH can do all the heating you need. If you have a thick screed, circa 100mm you can charge the floor like a storage heater on mostly cheap rate (E7 or similar). This takes a hit on CoP, but the electric is cheap.

You can get cylinders in just about any shape you want, or get it made to the size that suits you. Get one with a 3m2 coil.

thanks again … who are likely to make a cylinder to the size I need ? ( if no off shelf fits my space ?) I seem to you recommending Ideal as a good cylinder, some time back , do they make bespoke sizes ?
thanks again

JohnMo · February 26

Ideal just rebadge cylinders so not likely to make one off.

Try these

https://www.cylinders2go.co.uk/

markocosic · February 29

On 26/02/2024 at 07:43, JohnMo said:

Why the added complications, UFH is fine on its own for heating. Can do cooling also, just flow at 15 degrees, will knock the extremes of summer heat off and cost next to nothing to do.

It's not particularly complicated (no more so than UFH), gives greater freedom over floor finishes, can be more responsive than UFH where required, is materially better at cooling (more than just knocking the edge off; better distribution of coolth for comfort purposes), and similarly zero maintenance.

Edited February 29 by markocosic

Small ASHPs / Units primarily for DHW

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