Lurch88
|
| posted on 12/9/12 at 07:33 PM |
|
|
Air Water Heat exchangers
Anybody got any experience of Air Water heat exchangers
I have a man coming around to give us a quote to take out our oil fired boiler
and replace it.
Good Idea ?
Cheap to run ?
Give out enough heat?
What about fitting PV cells on the roof to power the pump, does that make it more viable ?
|
|
|
|
|
coyoteboy
|
| posted on 12/9/12 at 07:45 PM |
|
|
Are you meaning heat pumps?
Air-water meaning which way around (there's a few different possibilities - air outside water inside, water outside air inside etc etc.
Heat pumps are very effective but as far as I'm aware you can't use them like normal heating - you get best results with low temperature
differences with heat pumps (highest coefficient of performance).
Be wary, they rarely get their quoted COP.
PV cells are very pricey, what power does the pump take? IF you don't have a battery bank and inverter setup you won't be able to power
your pump during the evening/night/morning without mains use. Most folk turn their heating down during the day when it's bright.
[Edited on 12/9/12 by coyoteboy]
|
|
|
big-vee-twin
|
| posted on 12/9/12 at 07:56 PM |
|
|
Unfortunately most people who sell them quote massively ambitious figures regarding heat output and COP they usually quote figures at an ambient
outside temp of 7 degrees at a water temp of 35
For them to work effectively in the uk they have to operate at ambient temps of minus 4 or lower with water temps of 50 degrees if using radiators so
their actual efficiency is much less, they usually depend upon internal electric elements to do the heating at low external temps because the heat
pumps can't give out enough heat.
They are a heating appliance which looses capacity the colder it gets outside.
You would be much much better going for a Biomass boiler.
The heat pumps do work if designed correctly but operate at much poorer efficiencies than advertised
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
|
|
|
Lurch88
|
| posted on 12/9/12 at 08:01 PM |
|
|
It would be Air outside to water inside
then heating my existing radiator set up
taking the place of combi oil fired boiler
There are large grants £850 to install
then £850 per year for 11 years to use
Makes it all sound very atractive !!
|
|
|
hobbsy
|
| posted on 12/9/12 at 08:36 PM |
|
|
From the small amount I've read the Renewable Heat Initiative grants/payments make what would not be worth the money worthwhile again through
subsidy. It's more likely to be worthwhile as you're not on the gas grid - oil is expensive.
Interested to know which way you go as I have 3kW solar PV and thought that if I can get the RHI payments an ASHP could be a viable replacement for my
old boiler. Not ready to leap just yet though.
|
|
|
tegwin
|
| posted on 12/9/12 at 10:05 PM |
|
|
Lurch. I did an enormous amount of work on ASHP about 6 years ago.
My response is going to be long...
My grandmother had had one fitted about 22 years before, it had worn its self out so I specced up and installed a new one.
The unit I put in is a 12Kw ASHP (requires 2.5Kw of electricity). This just about warms the house via 17 conventional CH radiators. Its a standard Y
plan with pumped CH and HW.
The system is not ideal in any way shape or form but as the origional system 22 years ago was designed like that... My grandmother being set in her
ways would have nothing different...Consequently the house is never warm!
I have actually had to add in an electric 9Kw heater in series with the ASHP to supplement the heat during the coldest time of the year.
Ok so the ASHP provides all the hot water during the summer and contributes to the heating during the mild parts of the year. In the winter however it
provides very little. With the 9Kw boost heater running we can just about heat the house above 18c. (the actual heatloss of the house is around 22Kw
via 17 rads!)
On an average mild day the heatpump alone will (eventually) heat the water in the loop up to around 50c. (with a temperature differential across the
pump of 8c)
So from the above, yes, you can use an ASHP in replacement of a gas boiler...but its not a good idea atall.
The system I wanted her to have installed was a bit more complex.
It involved a 1000 litre thermal store, solar panels, ASHP and a gas boiler (or immersion type boost).
Solar would heat the very bottom of the thermal store, the ASHP (or ground source) would heat the middle of the tank and the gas boiler could be used
to top up the heat if ever needed. From that thermal store you can draw off water via heat exchangers for underfloor heating (35c) or space heating
(50c). Plus have direct hot water on tap via an additional heat exchanger.
Ok, so that little lot is not cheap but over about 20 years it would have paid for its self....Perhaps Ok on a new build but on a retrofit, not so
ideal.
For your situation..... Dont even think about PV to power the ASHP... without enormous battery banks you would never be able to run the
compressors.
I would be looking to fit the largest solar hot water array you can (ideally in two loops, one high gain and one low gain). Feed that hot water into a
thermal store. If you size it correctly you would get 90% of your hot water from that. You would need something else however to top up the heat when
the sun fails to shine.... If you have the ground (or can put in a borehole) ground source is more consistant than air source... Or fit a biomass
boiler, or if your oil boiler still works, keep it to just "top up" the heat if the renewable solutions cant quite cope during the coldest
spells.
Either way on a DIY basis for thermal store, solar, piping etc you would be looking at around £3000+.... Plus maybe another £2-3K for a decent heat
pump be it ground or air source.
Back when I installed the ASHP there were no grants for air source, only ground... and even with the grants you need an installer signed up to the
scheme which was going to cost more than I would ever make back from the grants....
If you have any questions regarding my above ramblings... drop me a U2U...
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
snapper
|
| posted on 12/9/12 at 10:08 PM |
|
|
They talked about these on Rip off Britain program, UK houses are not insulated enough and the electric backup heater fires up a lot costing you a
fortune.
Gas boiler is still more controlable and cheaper IMHO
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
tegwin
|
| posted on 12/9/12 at 10:14 PM |
|
|
quote:
Gas boiler is still more controlable and cheaper IMHO
With the current price difference between gas and electricity and the higher cost of installation you might be right in the short term....
But I suspect the price of gas will rise pretty dramatically over the next 5 years.... so installing renewables over a 10-20 year life cycle would be
worth it...
You would have to look at this on a house by house basis....
I should add to my above post that my grandmothers house is a leaky as a sieve...
If the house were a small sealed bungalow type thing I would not hesitate for a second to fit the ASHP on a Y plan without a thermal store atall!
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
hobbsy
|
| posted on 12/9/12 at 10:14 PM |
|
|
In the short term I'm probably going to do nothing with mine (I don't happen to live there anyway at the moment!)
When I return I may build / buy and then install one of these proportional controllers than uses the existing 3kW immersion in the storage tank to mop
up all *excess* solar PV generated (i.e. it won't ever use more than what is spare). Savings aren't massive at the moment (probably
<£100 per year as gas is still quite cheap) but you don't lose anything by doing it at the moment as the export amount isn't measured
just estimated at 50% so you might as well do something with it 
Tempted perhaps to upscale this to either a second storage tank / thermal store and perhaps try and get it to work at the other house that has a combi
but would require quite a few valves to pre-heat incoming water etc.
I haven't done the maths yet around the RHI to see if it could be profitable for the aggro but I take your point that an ASHP as the sole
replacement for a conventional boiler is probably a bad idea! And trying to power it off solar PV alone is an even worse idea. I keep forgetting
that the power needed to run the compressor is massive so unless you've got a big PV array at max power it won't be enough. Whereas
dumping excess power to a thermal store or electric under floor heating or whatever (as a simple resistive load) is easy.
|
|
|
Bare
|
| posted on 13/9/12 at 03:23 AM |
|
|
Using electricity to heat water is Laughably inefficient. Even If gas cost more than electricity, it would still be cheaper.
Some bespoke Boilers are Very Efficient and get every last bit of value out of the heating flame.
But like anything of quality worth owning ; Not free.
|
|
|
cliftyhanger
|
| posted on 13/9/12 at 06:39 AM |
|
|
I suspect all the technology and gizmo's needed will drop massively in price once more people buy them. ie they become viable. Just look at what
happened to the price of condensing boilers, halved overnight when they had to be fitted. I expect the same to happen to heat pumps and so on in the
next 10-20 years. Meanwhile, buy a jumper. Insulate everything.
|
|
|
Lurch88
|
| posted on 13/9/12 at 07:16 AM |
|
|
wow
fantastic responce from the forum again !!
You guys never cease to amaze me
Thank You
Lurch
|
|
|
