Considering ASHP in old property

myhandle

Hi Forum,

I own an old property which is currently heated by oil fired CH, this provides hot water too which I can heat with an immersion heater on Economy 7, I tend to do this on weekdays to let the CH take the oil without the distraction of heating water too.

I am interested in an Air Source Heat Pump, but do wonder whether the units available for a single phase supply are up to the job of heating this house. The floor area is approx 2000 sq. ft, however insulation is poor due to the the age of the house and its solid walls. Insulation could doubtless be improved, its a listed building so would have to be done properly and with appropriate consent, considering internal insulation as we can afford to lose a little space in the coldest rooms.

My main question is whether it would be effective to run an ASHP overnight on the cheap rate electricty (abour 4p per unit currently) if a pump is available with a high enough output. I've played with heat loss calculators which give me figures of between 11 and 20 kW to heat the house in winter with its current insulation levels. With Economy 7 I could presumably run a reasonably large unit overnight for under a pound, and then use it through day as dictated by a suitable contol system.

GSHP could be a consideration too as we have the ground space, but these pumps do not appear to be able to heat water hot enough for domestic hot water provision. Also GSHP appears more costly to install.

Any thoughts ? Just how good are these units through the winter (we are in Lancashire not far from the coast).

thills

Hi. I too have been looking @ASHP for a property not so well insulated. It's a pity people like the carbon trust do not have more advice or test results. Whatever the property, if you cant use gas, than its going to cost a fortune up front to get a system that is kind to your pocket & to the planet.
But what will give you the best heat for your ££s?
How can you be confident you dont spend big money, and get a house that will not keep warm (as seems possible with low water temperature systems).
Perhaps, look at Sanyo Eco which uses CO2 refrigerant, runs much hotter.... I think

myhandle

Yes, I do feel I need to be looking at a system with a high temperature output, as fitting underfloor heating is not going to be an option, increasing radiator size perhaps is as many of the existing installed rads date from the 70s and are single chamber (is that the correct terminology, they are thin).

I've read of DeLonghi, Sanyo and Mitsubishi units with high outputs, there may be others on the market.

There should be a grant of £900 or so for fitting one of these as they count as microgeneration, don't know if that is dependent upon having adequate insulation in the first place.

Cardew

myhandle wrote: »

My main question is whether it would be effective to run an ASHP overnight on the cheap rate electricty (abour 4p per unit currently) if a pump is available with a high enough output. I've played with heat loss calculators which give me figures of between 11 and 20 kW to heat the house in winter with its current insulation levels. With Economy 7 I could presumably run a reasonably large unit overnight for under a pound, and then use it through day as dictated by a suitable contol system.

If you contemplate an ASHP running on Economy 7 cheap rate electricity, I would have thought it essential to have a large heat store.

Would your saving even then, compensate for the extra price you pay for all the electricity used in the other 17 hours - not just for heating but your 'normal' electricity consumption?

arty68

All heat pumps work on the same principle so the higher the output temperature the less efficient they become. As for running them overnight the problem is what you gain in cheaper electric you lose in efficiency as the temp at night tends to be lower.

So basically you need to insulate as much as you reasonably can and change your rads so they can work at a lower temp.

Have a look at:-

http://www.nottenergy.com/energy-costs-comparison3

for best ££ for your heat.

So unless you have an old oil boiler that need replacing anyway you will be better off spending you money on insulation.

paceinternet

Insulate where you can first.
You don't have to have a high temperature (70 degC) to get the 20kw into the house. Radiators can run at lower temperature, say 50 degC from an ASHP, but will output a lower kw at deltaT of 30 deg instead of deltaT 50 deg which they normally quote their output at.
Look at http://www.stelrad.com/UK/docs/elite.pdf page 7 and you will see the output is about 50% less at deltaT 30 than 50. So, if you have single panel radiators, replacing them with K2 double panels will often achieve the output.
This is why underfloor heating is good because you get the surface area to dissipate the heat.

But to move on, E7 is unlikely to be the right tariff for a heat pump installation as said above.
You are however, very well equipped to creat a solution by having an air to water ASHP, with your oil boiler as the auxilliary heating source for when it can't meet maximum demand at the lowest outdoor temperatures.
And, you have an immersion heater so that you can raise your hot water from 50 to 60 daily or weekly to disinfect against legionella.

Cardew

arty68 wrote: »

All heat pumps work on the same principle so the higher the output temperature the less efficient they become.

Well said.

That should really be a 'health warning' for prospective ASHP customers.

The reason why heat pumps are so efficient for swimming pools is they are at their best raising a lot water a few degrees, rather than a little water a lot of degrees!!

Too many adverts seem to stress that they can:

1. produce water at very high temperatures

2. have very high COP

Without making the point of the connection between those qualities.

It's like saying

!. my car can do 140mph

2. My car can get 40mpg

without making the point that I won't get 40mpg at 140mph.

albyota

However, if in the warmer months (for heating your hot water 365 days a year) you get a COP of around 4 or even 5, whereas in the colder months the COP drops to about 1.8, the average COP over the year is......annual COP of 3.4...... why then isn't 340% or 350% efficiency any good? No health warning needed, if we only take notice of cardew's opinions we're never going to get anywhere with carbon reduction....or saving money on our fuel bills........written by someone who has an Air to water Source Heat Pump Ecodan installed over a year, and at this very moment is sitting in a comfortable house at 23 degrees inside....minus 1.7 outside with total annual electric only fuel bill of £804 - 4 bed house family of four.

By the way Sanyo ECO CO2 has a two stage compressor that does heat water to 65 degrees without electric back up and at an annual COP of 3.75, the altherma HT will do 80 degrees.

You Decide......!!!

arty68

It's not so much of a health warning just something people should be aware of and design there system accordingly. Mine should be up and running in a couple of months so I'll find out for real what there like and keep people updated.

Cardew

albyota wrote: »

However, if in the warmer months (for heating your hot water 365 days a year) you get a COP of around 4 or even 5, whereas in the colder months the COP drops to about 1.8, the average COP over the year is......annual COP of 3.4...... why then isn't 340% or 350% efficiency any good? No health warning needed, if we only take notice of cardew's opinions we're never going to get anywhere with carbon reduction....or saving money on our fuel bills........written by someone who has an Air to water Source Heat Pump Ecodan installed over a year, and at this very moment is sitting in a comfortable house at 23 degrees inside....minus 1.7 outside with total annual electric only fuel bill of £804 - 4 bed house family of four.

By the way Sanyo ECO CO2 has a two stage compressor that does heat water to 65 degrees without electric back up and at an annual COP of 3.75, the altherma HT will do 80 degrees.

You Decide......!!!

Whoa,

I am not knocking ASHPs as you well know.

We have had this discussion about the Sanyo before a couple of times.

The principle is exactly as stated above, as you increase the water temperature the COP falls off. My analogy of a car is valid.

Your statement in the last paragraph is exactly the sort of misleading comment(albeit unintentional) I have been going on about.

Here is the sanyo advertising website.

http://uk.sanyo.com/aircon/products/CO2-ECO-Heating-System/Introduction/

There is nothing to support your contention it " does heat water to 65 degrees without electric back up and at an annual COP of 3.75,"

It does heat domestic hot water to 65C - but at what COP? and at what outside temperature? Incidentally all models do have auxillary electrical heaters of up to 15kW!!



What is the central hot water temp at the various COPs quoted?

Agreed it gives a COP of 3.75 with an outside temperature of 20C

Even the best of the larger units only claim a COP of 3.3 at 7C - dropping to 1.6 at temperatures not experienced in UK.

paceinternet

http://uk.sanyo.com/aircon/products/CO2-ECO-Heating-System/90kW-Single--Three-Phase/
You do have to be careful reading the spec on these things, because most do not give you lots of performance detail. A "seasonal COP" will not be the same for all locations in the UK. The Sanyo unit in my link above does have auxiliary electrical heating of 12kw, and that is because it needs it in certain temperature situations.
It shows a COP of up to 4.1 at:
*Outdoor temperature 25℃, Inlet water temperature 30℃, Outlet water temperature 50℃
(tell me why they quote 50 when the big selling point for CO2 is that they can achieve 65+. Yes you are right. The numbers look better at 50 than 65. Outdoor 25, thats a very good summers day here in the UK)

And it also quotes a COP of 1.8 at -15 degc outdoor temperature. Inverter units normally turn down their power consumption at lower temperatures so what is maybe a 3kw compressor may only be using 2kw and therefore outputting 3.6kw, but certainly much less than its model rating of 9.

I am a supporter of heat pumps, and used over a season/year, I believe they will be very cost efficient. But they all follow a similar physical process and are more efficient at lower output water temperatures.

The capital cost of a heat pump sized to meet maximum demand at the minimum outside air temperature can be prohibitive. But sizing to meet demand at around 7 degC, and then having some other auxiliary heating will be cost effective for many people.