Sustainable Homes website

[summerdays]

If you've seen an airco unit bolted to the outside of a shop you've seen an air-source heat pump. It's just being used for cooling, not heating.

Oh yes I've seen them...
Thanks everyone for the above information ...

 

[slowmotion]

The Energy Saving Trust has published a brief article describing the results of a field trial of ASHPs.

http://www.energysav...urce-heat-pumps

Typical efficiencies are 1:2.2

 

[Archie_tect]

The Energy Saving Trust has published a brief article describing the results of a field trial of ASHPs.

http://www.energysav...urce-heat-pumps

Typical efficiencies are 1:2.2

Efficiencies down to 1:2.2 seem a bit low Slowmotion but results depend on external air temperatures... possibly in the last winter the air temperatures were severe during Dec/ Jan/ Feb which meant monitored ASHPs were defrosting more than previous tests. Putting the ASHP in a less exposed location or shielding it from extreme frost and cold would help.

 

[slowmotion]

AT, I'm fairly sure that some of last winter's weather was included in the trial, but have no idea how this affected the efficiencies. Here is an article from the Guardian.

http://www.guardian.co.uk/environment/2010/sep/08/heat-pumps-green-heating

 

[summerdays]

Well we've had our first visit which has inevitably raised as well as answered questions.

You can't use the power in the event of a power cut as it is DC and the bit that converts to AC is run by the mains.
Our roof is about 35 degrees or just above
(Rather weirdly he didn't bring a compass with him and trusted us to know which way was south facing!)
Lots to think about with which panels to consider - different sizes so we would require different numbers of them.

Not sure about what the best looking layout would be on the roof, and whether to try and fit the water up there as well.

 

[Night Train]

I've been looking in to this, as well as studying it as a MSc for a while.

If I had the money I would like to make use of my roof. I have 10sqm of south facing slope at 50deg and about 18sqm of west facing slope at 45deg. It would be ideal for both heating and pv.
I would use the pv to charge batteries for the electric car rather then get the feed in tariff as I could then do the work myself and not have all the red tape (except to wrap around dodgy electrical connections ).

 

[Archie_tect]

Well we've had our first visit which has inevitably raised as well as answered questions.

You can't use the power in the event of a power cut as it is DC and the bit that converts to AC is run by the mains.
Our roof is about 35 degrees or just above
(Rather weirdly he didn't bring a compass with him and trusted us to know which way was south facing!)
Lots to think about with which panels to consider - different sizes so we would require different numbers of them.

Not sure about what the best looking layout would be on the roof, and whether to try and fit the water up there as well.

Sounds a bit odd I must admit. Don't understand why the DC to AC converter couldn't be wired in anywhere so are they offering you PV/ FIT for your use or is it the electric company or a subsiduary getting in on the act?


Oh and here's a link to the discussion started about the efficiencies of Air Source Heat Pumps...
http://www.sustainablehomes.co.uk/index.aspx?dm_i=8T3,AO3F,WDZMQ,TDDA,1


If it was me- I'd always do solar heating first as that is constant long-term free energy and hot water. Heating water is a totally inefficient way of using electric [gas isn't so bad but even then is only 90% efficient and it won't last forever] however electric uses expensive primary fuel to produce heat to produce steam to turn a turbine which generates electric which is lost on the grid in transmission which you then use to produce heat again to provide hot water.... roughly 20% efficient, against 'free' solar power. It's a no-brainer really.


The installer should prepare a plan arrangement for the array with the orientation [not a guess!] and the shadow extent projection from any obstructions onto the roof for the year long daily sun path across your roof to assess where the panels should be located. If he doesn't do this he is not competent. I leave that to your discretion.

 

[summerdays]

It is solar PV with FIT and also the solar water heating that we are considering.

The discussion with the number of panels resulted from whether we wanted to fit the full amount (apparently 3.5 kw is the normal max due to the amount the electricity company can accept without checking with the electrical company - sorry I'm not very good at taking in all they said), and two different types of solar pv hybrid or ...???? (one of those seemed to be more efficient but more expensive than the other, as well as being different shaped). Then it was whether we also wanted the solar hot water on the roof - best site for the installation but may impact on the number of solar PV we could have. We are also trying to think of alternative sites for the solar hot water pipes but at what loss of output ... so mounted horizontally on a west facing wall or possibly on a south facing wall.

He did think that in the future you may be able to add to the converter so that it could run off the DC power it produced (think I got that right).

He didn't think there was any problem from shadowing apart from the chimney.

 

[Archie_tect]

He didn't think there was any problem from shadowing apart from the chimney.

Any overshadowing reduces the PV generation potential as it is the equivalent of trying to run something by putting a dead battery, along with 3 new ones, into a torch and hoping it will still work. Avoid putting any panels up where they will be shaded as you are wasting the money you'll be spending and getting no return for it.

I'd still put solar hot water up first facing south and at 30 degress and infill with PV- your returns on PV are really only effective with Feed in Tariff due to the cost of the cost of installation. Of course an installer would want to fit PV first as he gets paid up to 4 times as much for less effort.

Only put PV or solar heating inclined onto vertical walls as a last resort.

 

[summerdays]

Thank you - all this information is being absorbed ... (even used during the consultation - you have managed to say it in understandable terms), even something as simple as how important to regard water vs PV is useful to me.

He showed us which parts of the roof were usable - leaving space around and above the line of the chimney. And we have yet to arrange the date for a second company to come and give us a quote though we have been in contact with them.

 

[Yellow Fang]

It is solar PV with FIT and also the solar water heating that we are considering.

The discussion with the number of panels resulted from whether we wanted to fit the full amount (apparently 3.5 kw is the normal max due to the amount the electricity company can accept without checking with the electrical company - sorry I'm not very good at taking in all they said), and two different types of solar pv hybrid or ...???? (one of those seemed to be more efficient but more expensive than the other, as well as being different shaped).

I don't know what he means by two types of solar PV. PV panels are usually constructed of silicon, which can be monocrystalline, polycrystalline or amorphous. Monocrystalline is the most expensive and also the most efficient, but polycrystalline is close. Amorphous silicon panels are usually a fair bit cheaper but a lot less efficient. They can also look quite different, for example thin film PV is amorphous. There are other materials out there too: Gallium Arsenide, Cadmium Telluride and Copper Indium Gallium Selenide, but normally it's silicon. There are some weird and wonderful PV panels around now, although probably quite expensive. Some are semi-transparent, so they can be used for shading. Some are roof tile shaped.

There are at least two types of solar hot water panels he could be refering to. There are flat plate collectors and evacuated tube collectors. Evacuated tube collectors are arguably better, but more expensive.

I noticed at a recent exhibition that combined PV and hot water panels are starting to come onto the market.

Then it was whether we also wanted the solar hot water on the roof - best site for the installation but may impact on the number of solar PV we could have. We are also trying to think of alternative sites for the solar hot water pipes but at what loss of output ... so mounted horizontally on a west facing wall or possibly on a south facing wall.

He did think that in the future you may be able to add to the converter so that it could run off the DC power it produced (think I got that right).

He didn't think there was any problem from shadowing apart from the chimney.

The problem is that your appliances won't run off DC. Most appliances have A to D converters in them, but run off AC mains. There are 12 DC appliances designed for caravans, house boats and such. Unless he was talking about the inverter, which converts DC from the PV panel to AC. The power companies have a problem with solar PV panels putting power on the line when there's a power cut, in case the maintenance crew get a shock. I expect most systems just output everything you generate to the grid and you import what you need back off the grid. I don't suppose many inverters currently allow you to isolate yourself off the grid and re-direct the electricity to your own use. I suspect it could only work if you have some batteries to store the energy, because your appliances need constant power, which your PV won't provide. The need to keep your batteries charged would probably mean trading off income for independence from the grid.

He should be able to tell whether there will be shadowing from the chimney. There's software that allows you to work it out. Generally in the summer, shading is less of a problem because the sun's higher in the sky, and this is when you are generating most electricity. Shading can cut down the amount of energy you generate by a lot more than just the proportion of area shaded, but it depends on the design of the panel and how they're wired up.

 

[Yellow Fang]

This is what you need, combined thermal and photovoltaic panels.

On 2nd thoughts, possibly not.

 

[Archie_tect]

This is what you need, combined thermal and photovoltaic panels.

On 2nd thoughts, possibly not.

As the PV2 prices come down they'll definitely be worth looking at YF! Great for south facing conservatory roof and atrium roofs to reduce summer overheating.

Visisted the Devonshire Building in Newcastle University last night- what a disappointment it was.

The EPC on the wall listed it as a "G" with a rating of 214 with the industry standard for that type of building being 100 and excellent being well below 100.... and this is supposed to be a ground-breaking design using a massive PV array on the sloping roof and wall. Badly overshadowed so reality never matched the model. The PV array was installed in 2004 and was completely replaced in 2008/9- goodness how much it cost. Modern units are becoming more viable and with FIT it makes sense IF you've got the money to install as I keep saying.

 

[Yellow Fang]

The reason I thought they might not be suitable for Summerdays was that one was designed for swimming pools, one designed to work with a heat pump, which I guess would be difficult to retrofit to an existing system, and the other was pretty expensive. The last one says it's a combination of PV and thermal, but does not say whether it's space heating or water heating. I suppose they mean water heating.

 

[Archie_tect]

PV2 combination PV and solar hot water are too experimental/ expensive yet for domestic use.