Air Source Heat Pumps

samtheman1k

Frostybelgian wrote: »

Hi, thank you for your response,yes it is a big house, there are five people having showers and all ancilliary water usage. During the winter months the water produced was not hot enough to have a bath in. The unit was supposedly sized for the property using the SAP calcs and it is is an HP1AW 10SE-2AG, the power input is listed as (A2/W35) - 2.5kW, the Ph is 8.9kW the COP is 3.6, Max Power Input 8kW, Max Total Power Input 11.8kW. The heating elements were on most of the time during winter and we werer struggling to keep the house warm, 21C in living areas 18 in beds. We have the CH output at 35C, the spacing of the underfloor heating pipes is 100mm to allow for lower output temperature.

according to my calcuations, if your bill is £600pm, then you are using 200kwH per day (based on 10p/kwh)!!!! That is equivalent to you running your HP at max power 24 hours a day (with the electric boost I think from your figures)! Your HP is either seriously underpowered, and thus have to use constant electric boosts, or something else is drawing the electric.

Bare in mind that some HP systems can't supply heating and hot water simultaneously, so that may explain why you have no hot water.

Frostybelgian

Yes thats right, one day we used 236kW/h!!

The system we have is designed(?) to do both hot water and central heating.

Do you know how to calculate the heating requirement for an ASHP?

Many thanks

richardc1983

Yes but many systems cannot heat hot water and heating at the same time.

This goes for many combi boilers, the hot water will always take priority over radiators.

samtheman1k

Do a search for 'BTU requirements' and you'll find loads of calculators: e.g. http://www.theradiatorcompany.co.uk/heatoutput/

Calculate the BTU/Watts required for each room, add them all up to get the house requirements, and that is the minimum required power from the boiler/ashp/whatever you require. Note that with heat pumps, if you calculate the BTU required for a room, it is not directly correlated to the BTU figures of radiators as they normally assume a water temperature of c80degC. You have to oversize your radiators by a minimum of 20%, depending on insulation etc (not the same for UFH though).

zolablue25

paceinternet wrote: »

Also, I hope you recognise that the heat pump part of the heat input when operating at a COP of 3.6 will be costing less than 3p per kwh. The direct auxiliary heat will be costing around 10p per kwh. And a modern efficient mains gas boiler will be costing around 3-4p per kwh, all depending on your tariffs.

So, basically, if you are on mains gas there is no point investing in a heat pump as the savings will be nil/minimal?

Cheers

samtheman1k

richardc1983 wrote: »

Yes but many systems cannot heat hot water and heating at the same time.

This goes for many combi boilers, the hot water will always take priority over radiators.

Yes, that depends on whether you have a thermal store and whether it is direct or indirect.

richardc1983

samtheman1k wrote: »

Do a search for 'BTU requirements' and you'll find loads of calculators: e.g. http://www.theradiatorcompany.co.uk/heatoutput/

Calculate the BTU/Watts required for each room, add them all up to get the house requirements, and that is the minimum required power from the boiler/ashp/whatever you require. Note that with heat pumps, if you calculate the BTU required for a room, it is not directly correlated to the BTU figures of radiators as they normally assume a water temperature of c80degC. You have to oversize your radiators by a minimum of 20%, depending on insulation etc (not the same for UFH though).

I reccomend oversizing the heat pump to cope with the winter temps, always helps to have extra capacity on hand even if sized correctly then its not working flat out all the time.Also user states they have underfloor heating so does the same apply then they already stated they have the piping closer together.

paceinternet

So, basically, if you are on mains gas there is no point investing in a heat pump as the savings will be nil/minimal?

Difficult, but a few things to consider.
1. how efficient your existing gas boiler is.
2. do you feel better with an eco friendly system.
3. where are gas prices going versus electricity prices.
4. a more detailed assessment of your heating and hot water use, particularly in the months when outdoor temperatures are giving a higher COP, may provide some savings. But it would be difficult to justify the capital cost versus doing nothing if your gas boiler is working ok. If your gas boiler needs replacing, then you may get some benefits with the current electricity/gas price relationship.
5. servicing costs: depends if you go with annual gas boiler servicing, and some would say a heat pump only needs periodic cleaning, which you can do yourself or get done for quite a low cost.

richardc1983

zolablue25 wrote: »

So, basically, if you are on mains gas there is no point investing in a heat pump as the savings will be nil/minimal?

Cheers

Wrong, you make substantial savings if sized correctly etc.

A heatpump you get about 3kws of heat out of it for every kw of electric it consumes.

BOilers are less than this you get approx 1kw of heta for every kw it burns. However gas is cheaper which is why most people have gas.

arty68

Hello,
I'm currently building a house and am trying to decide the boiler type for my heating and hot water.
The new house is not on mains gas so that's out of the window.
There are too many trees on site to have GSHP (bore hole option very expensive)
The lane is too narrow for the LPG tanker.
Which leaves me with Oil,Pellet or ASHP.
My questions are:-

In the real world do they work ?

Is there a good ASHP that will do Heating and hot water that is reasonably priced ? (Danfoss and NIBE seem to be the best but are expensive).

My plan was to have UFH downstairs and rads upstairs is an ASHP suitable for this ?

Any help with the above would be much appreciated .