Puff The Magic Wagon!

iTrader: (2)

So I have an ASHP in my weekend home - costs a fortune to run.

What would be better, Solar Water on the roof providing hot water or 4kw Solar PV with battery backup (off grid system)? Both cost roughly the same.

Aim is to cut down on my electricity usage as much as possible.

So would I be better off using Solar Water to provide all my HW (and then cut down on electric to the ASHP that way) or Solar PV to mitigate all my electricity cost.

andy97

iTrader: (1)

We have a ground source heat pump to heat our house and water. Its uses 5kw of electrical energy to generate 15kw of heat energy, ratio 3:1. My costs are roughly equivalent that of my friends houses, but my house is considerably bigger.

If you want to cut down on electric use PV solar. Caveat, must have large south facing roof clear of obstructions.

Dont bother with battery backup, costs a fortune, doesn't have long life. Is this UK? You know you get a feed in tariff that assumes you use 50% of the PV energy. The word is assume, just use all the capacity and still get tariff(not alot these days)

ALi-B

iTrader: (1)

With air source, the efficiency ratio or better termed as Coefficient of Performance (COP), varies massively on climatic/ambient conditions with respect to the outdoor unit's location relative to ambient humidity and its need to defrost including whatever means are used to detect evaporator icing; some basic units just used a timer! So if the evaporator ices up it reduces efficiency.

The market was flooded with units that stated high COP ratings but the real life COP ratings were less efficient, as the manufacturer's rating didn't always include the defrost cycles and were rated in favourable test conditions or the actual installation isn't conducive to obtain the best performance. The swimming pool heat pump sector also suffers the same issues; You can buy two heat pumps with identical specs, but one can perform better than the other, the price usually gave a clue, however that was not always clear cut as some brands would re-brand lesser/unknown units.



So if I was in your shoes I'd try to indentify is if the HP setup actually is efficient...if the evaporators are icing up excessively iceing up (restricting airflow and heat transfer area) which could happen in areas of cold and high humidity then you could be only running a COP of 2, or even 1, maybe less if the units are totally iceing up (and I bet they did last week if it was being used).

PV has its avantages; if you can sell back to the grid when the property isn't being used you will offset useage and any inefficiencies in the heating system.

I would only consider solar HW after throughly checking the real world efficiency of your existing HP and see if it can be improved and only consider investment in alternative heating sources if it's found lacking. Bit tricky with home heating as there are a lot of variables. My main HP experience was commercial stuff and swimming pools, the latter was pretty easy to model as it was a relatively closed system. Assuming this HP for for wet heating, you can do measurements of the DeltaT temperature of flow and return temps at particular ambient temps, and logging what temp rise you get at given return temps at given ambient temps, also whilst measuring electrical current draw.

So at X ambient, X interior, you get X temp rise at X return temp at X current draw (at X voltage to get your watts ). The temp rise will be the energy put into the heating water and its this what you will be converting to watts and comparing to the energy going in. My thermodynamics is rusty so I'll lay off the maths before I type it down wrong

It would take a fair bit of time and you'd only take your measurements when you would typically using the system. But you could find issues that you can fix and improve it without too much cost.

alcazar

iTrader: (2)

We have the solar PV panels, we see some reduction in leccy bills, but also best part of £1000 a year in payments, (we JUST beat the deadline for the £0.46 per kWh payment).

Bro in law has solar water heating. North of England (Humberside), he pays nothing for hot water between mid March and November each year.

Tidgy

im yet to see anyone make any profit from solar panels. the systems seem to cost more than they ever make

Pross

iTrader: (3)

ASHP's are crap. Council fitted one to our house last year, never worked properly. It blew up in january leaving us 5 weeks without heating. It was like a grenade going off against the wall when it went bang.
As for the cost? £10 per day to heat a small 3 bedroom house.

Tidgy

£10 x 30 days average £300 x 12 = £3600

Pross

iTrader: (3)

You think im joking?

Tidgy

no no, i worked for a building service firm so well aware of how poor the returns are costs wise

Solar never pays for itself either, in fact renuables just arn't cost effective no mater what you do.

Pross

iTrader: (3)

We didnt even have a choice.

They came in and blocked up our chimney and fitted the things to the whole street.

Open fire used to heat the whole house.

Tidgy

sounds about right for councils. shame you can complain cos they are now costing you 10 times as much