solar panels V air source heat pump for DHW

snow mad

I have been looking at air sourced heat pumps for DHW does anyone have one. How are they performing? I would appreciate any info on the comparisons

The company I have been in contact with is claiming the system would provide me with 100% of my DHW for in or around 100euro/pa and hot water tank will be taken of the off the boiler so there would also be savings on gas.
would like to hear how much of a difference it has made to anyones heating bills and how much the system cost.

Do-more

What type of air source heat pump are you looking at installing?

Without knowing precisely what you are looking at it's hard to give you a definitive answer but it is possible to work out a ballpark figure.

A really good air source heat pump will have a COP of 4.2 but that figure is based on an ambient temperature of 7C and heating the water to 35C i.e. for underfloor heating not DHW.

With an ambient of 7C and heating the water to 45C the COP is likely to drop to around 3.4.

But it is not 7C all year round the temperature fluctuates so you have to look at the seasonal performance factor and allowing for defrosting in the winter and heating your cylinder to 60C once a week to avoid legionella you are probably looking at a SPF of 2.8 at best.

So based on those sample figures how much hot water is the claimed €100 per year going to get you?

Assuming an electricity price of 19cent/unit you will get:

€100/0.19 = 526 X 2.8 = 1,473kWhr of hot water @45C

An average family of 4 would probably use twice that amount.

You mention saving on your gas heating, so I assume you have that already or you are going to install it anyway. Either way I can't see how you will pay back the investment in a heat pump rather than heating your DHW with gas.

snow mad

Do-more wrote: »

What type of air source heat pump are you looking at installing?

Without knowing precisely what you are looking at it's hard to give you a definitive answer but it is possible to work out a ballpark figure.

A really good air source heat pump will have a COP of 4.2 but that figure is based on an ambient temperature of 7C and heating the water to 35C i.e. for underfloor heating not DHW.

With an ambient of 7C and heating the water to 45C the COP is likely to drop to around 3.4.

But it is not 7C all year round the temperature fluctuates so you have to look at the seasonal performance factor and allowing for defrosting in the winter and heating your cylinder to 60C once a week to avoid legionella you are probably looking at a SPF of 2.8 at best.

So based on those sample figures how much hot water is the claimed €100 per year going to get you?

Assuming an electricity price of 19cent/unit you will get:

€100/0.19 = 526 X 2.8 = 1,473kWhr of hot water @45C

An average family of 4 would probably use twice that amount.

You mention saving on your gas heating, so I assume you have that already or you are going to install it anyway. Either way I can't see how you will pay back the investment in a heat pump rather than heating your DHW with gas.

not really sure of the exact efficiencies of the system was more really looking for some one that had an ASHP installed for DHW to see what they taught of the system i dont really have any figures for my specific heat requirements so DHW/SP but what i am really after is running costs for such systems

P.S. I think the efficiencies of the system are only affected by bellow -2c so the cop will not change very much

Do-more

snow mad wrote: »

P.S. I think the efficiencies of the system are only affected by bellow -2c so the cop will not change very much

COP is effected by the delta T that is the difference in input and output temperature so the bigger the delta T the lower the COP.

Other factors will also affect overall performance such as the specific design of heat pump and the type of refrigerant used for example.

Once outside temperatures drop below a level where the heat pump has to defrost performance can fall very considerably, how much depends on how the defrost cycle operates and what controls are used.

Anyway I suggest you need to give us lots more information on your situation if we are to help you with a decision as there are so many variables involved.

What do you currently use for heating water and for space heating?

What size is the house and how many occupants?

Do you take showers or baths?

Read the recent thread on solar panels to get an idea of payback on them.

Without quantifying what you are looking at it is impossible for you to make a good decision on what is right for you.

You will find that there are very few if any other people using a heat pump for water heating and gas for space heating so you are unlikely to get any feedback on what it is costing them.

I am about to install an air source heat pump for both DHW and space heating in my new build, but if I had mains gas available I would go for that instead as the capital cost would be much lower.

jimmytom

Do-more wrote: »

COP is effected by the delta T that is the difference in input and output temperature so the bigger the delta T the lower the COP.

Other factors will also affect overall performance such as the specific design of heat pump and the type of refrigerant used for example.

Once outside temperatures drop below a level where the heat pump has to defrost performance can fall very considerably, how much depends on how the defrost cycle operates and what controls are used.

Anyway I suggest you need to give us lots more information on your situation if we are to help you with a decision as there are so many variables involved.

What do you currently use for heating water and for space heating?

What size is the house and how many occupants?

Do you take showers or baths?

Read the recent thread on solar panels to get an idea of payback on them.

Without quantifying what you are looking at it is impossible for you to make a good decision on what is right for you.

You will find that there are very few if any other people using a heat pump for water heating and gas for space heating so you are unlikely to get any feedback on what it is costing them.

I am about to install an air source heat pump for both DHW and space heating in my new build, but if I had mains gas available I would go for that instead as the capital cost would be much lower.

I am about to start build on my house. I am currently trawling through the info re air to water vs solar panels. Its a minefield.

I am currently proposing to install one of these two options for DHW and SH:

1. flat panel solar for Hot water with oil boiler and a back boiler on stove
2. air to water heat pump with oil back up

which would you consider a better option. House is 230 sqm, 4 beds, will have two occupants at first but more in the future - kids dependent. underfloor heating downstairs, rads upstairs. showers would be the norm in the house

Do More i see that you are about to install air to water for SH and DHW. Is there particular reasons which led you down this path.

Any advice gladly welcomed!

solarstudent

jimmytom wrote: »

I am about to start build on my house. I am currently trawling through the info re air to water vs solar panels. Its a minefield.

I am currently proposing to install one of these two options for DHW and SH:

1. flat panel solar for Hot water with oil boiler and a back boiler on stove
2. air to water heat pump with oil back up

which would you consider a better option. House is 230 sqm, 4 beds, will have two occupants at first but more in the future - kids dependent. underfloor heating downstairs, rads upstairs. showers would be the norm in the house

Do More i see that you are about to install air to water for SH and DHW. Is there particular reasons which led you down this path.

Any advice gladly welcomed!

My advice to you would be to put solar thermal panels on the roof and put in an air-source heat pump to supplement this in the colder months. PM if you want to see a working example of this.

Do-more

jimmytom wrote: »

Do More i see that you are about to install air to water for SH and DHW. Is there particular reasons which led you down this path.

Sorry for the late reply JT.

It's primarily due to a lack of other alternatives.

I'm building in Sweden and I'm not allowed to install an oil burner in a new build, no gas is available and the ground isn't suitable for a ground source heat pump.

I'm not keen on wood pellets or log burners so solar or ASHP are really the only options I have left.

Having more or less dismissed solar I have been re-visiting the numbers this week and have crunched the numbers again.

I figure if I install 50m2 of solar I can supply almost all of my space heating and DHW save for about 2000kWhr which is slightly less than what the heat pump should consume to do the same job.

Of course the solar will be a lot less reliable than the heat pump and it's unlikely that the reality will match the theoretical figures but the idea does hold a certain attraction and I will continue to investigate the possibilities.

rosepaddy

I have a heat pump but i also have solar the reasoning is i require only my solar circulation pump working to give me all my dhw needs for 6 to seven months. i have a big demand for my hot water my air to water is doing all my heating in the winter and i use night rate electricity shutting off the system before eight in the morning i have a meter on my system and can calculate my usage, it is a trouble free system, very cost effective, we use diffuesed radiation collectors enhancing solar contribution in the winter from switzerland, but , i would say thay all your dhw for 100 sounds great i dont think i could do that with my heatpump and solar.and i reckon i have a very economical package my heat pump is from sweeden

illionman

I am about to start build on my house. I am currently trawling through the info re air to water vs solar panels. Its a minefield.

I am currently proposing to install one of these two options for DHW and SH:

1. flat panel solar for Hot water with oil boiler and a back boiler on stove
2. air to water heat pump with oil back up

which would you consider a better option. House is 230 sqm, 4 beds, will have two occupants at first but more in the future - kids dependent. underfloor heating downstairs, rads upstairs. showers would be the norm in the house

Do More i see that you are about to install air to water for SH and DHW. Is there particular reasons which led you down this path.

Any advice gladly welcomed!

Hi all, sorry for late reply.

I have a geothermal heat pump for my underfloor heating and DHW. The heat pump is excellent for the heating but very very uneconomical for hot water. For DHW the heat pump heats a 300l cylinder to 55 degrees. This has a heat exchanger on top of it and when hot water is turned on the water in the cylinder is used to heat the cold water as it passes through it. It works fine, suply is good - can deliver hot water to 3 power showers together but it is very expensive to run. I am not sure exactly how expensive but this summer (if we get one) I intend to turn off heating and fit meters to electricity and hot water and work out a cost per litre. I think I will then look at an alternative for my DHW requirements. I would tend agree with oil back-up or a stove for the higher temperatures but not both. If you are willing to put up with the bother of a stove and have a supply of solid fuel at reasonable cost then this is a good option. (Not coal or wood by the bag) I would be careful about mixing a stove with back boiler with solar panels for DHW as the solar panels could be reduntant while the stove is operating.

purebokety

As far as i know a secondary heat pump for dhw is also and option.Where your air source can take care of your space heating without pushing the required temperature up to meet your DHW requirements, in doing so dragging down your COP or SPF. My understanding is that the secondary system is simply on for less time so costs are lower. I have not seen any studies done as of yet to see how this secondary system might compare with say solar thermal panels for your DHW.

Tommyboy08

purebokety wrote: »

As far as i know a secondary heat pump for dhw is also and option.Where your air source can take care of your space heating without pushing the required temperature up to meet your DHW requirements, in doing so dragging down your COP or SPF. My understanding is that the secondary system is simply on for less time so costs are lower. I have not seen any studies done as of yet to see how this secondary system might compare with say solar thermal panels for your DHW.

Noncence, two heat pumps, both air source, one for space heating and one for hot water?
How would that make any sense, they would both have the same performance on dhw so one would do the same job using a three way valve and hot water setting

purebokety

Nonsense ok good start to a reply highly informative.Secondly heat pumps for space heating have a lower temperature requirement than that of domestic hot water(solar panels).As your temperature needs increase your heat pump will drop its performance( cop spf) as a result.The second heat pump is used intermittently to reduce pushing the system above its design temperature in order to bring down its running costs.I can see why the valve is used a pre heat method.As I said earlier its just something I have heard and have not seen how this system of two heat pumps compares in performance to say a gshp(space heating) with solar for dhw

ivorfa

Have spoken to a renewable company today and they suggested a small air to water heat pump for space heating only they also suggested a water heating heat pump eg coolwex or similar for dhw would this system be any cheaper to run than a good air to water heat pump to do both heating and dhw

Tommyboy08

purebokety wrote: »

Nonsense ok good start to a reply highly informative.Secondly heat pumps for space heating have a lower temperature requirement than that of domestic hot water(solar panels).As your temperature needs increase your heat pump will drop its performance( cop spf) as a result.The second heat pump is used intermittently to reduce pushing the system above its design temperature in order to bring down its running costs.I can see why the valve is used a pre heat method.As I said earlier its just something I have heard and have not seen how this system of two heat pumps compares in performance to say a gshp(space heating) with solar for dhw

As I have said before, the one heat pump would do the same job as two seperate units(one for space heating and one for DHW)
The unit doing space heating with underfloor would have a setting of let's say 35C and a cop of about 4,
When it has to heat the DHW tank it's set point changes to 50C and then its cop will start to drop off to approx 2.5 by the time the tank reaches 50C, it then returns back to heating the underfloor to 35C and its cop again returns to 4.

The scenario of the house with two individual heat pumps,
Well the heat pump doing the space heating will have to be the same size as in the house with one heat pump and its cop and performance will be the same,
The secondary heat pump for DHW will also have a cop of 4 at 35C and will also drop to a cop of about 2.5 by the time the water reaches 50C,
So better of buying one heat pump as its less Capital outlay

I haven't just heard about it, I have seen it in place and it makes no sense, just costs more, neura do it, hautec do it,
I just can't see the benefit, you've now got two heat pumps that need maintenance!