DHW via Solar - Surprised at results

Patrickof

Hi,

Just did my first BER that had a retro fitted set of panels to provide DHW (no link to space heating, just hot water).

Considering that the system cost in excess of 4K to install I'm surprised at how little the effect is on the BER results.

(It's still a C1, the figures only change slightly when I remove the panels)

Am I correct in thinking that this is because the bulk of your oil/gas goes on space heating, and the DHW element of a heating system is really quite minimal.

Kinda make you wonder whether the cost benefit exists for a solar DHW system.

sydthebeat

what change did you make to the cylinder?

what was the energy value before, and after?

Patrickof

Just got an email back from the supplier with the DEAP instructions on it (he claims SEAI gave these instructions so I'll need to verify).

But, it states that the system IS the main water heating facility, so on the water energy requirements page it's different to the space heating tab - efficiency is 347%, efficiency adjustment is 0.7%. Fuel type is then electricity in the final tab.

The reason given is that the system is a hybrid - mix of panels and a heat pump. A refrigerant is used in the panels so they claim it does meet the entire water heating requirements (I am aware of S4.4 in the DEAP manual that says otherwise)

The solar panel info pop up window was (capacity 280L, not shared, 0.9 n0 and 20 a1), south facing 45 degrees no overshadowing.

With panels: C1, 154.32 and 32.82 CO2
Without: C1, 162.38 and 33.28 CO2

Not a significant difference.

Also, in relation to room in roof: the dwelling is a dormer bungalow, ie no partial walls on the first floor - entire is within the sloping roof - but with 2 end gables (included in my walls tab). DEAP has auto calculated the room in roof area for the building elements details. Do I also need to add the 1.5 m wide roof element that is the bottom part of the sloping roof (the bit thats usually used as storage) to make up the shortfall in roof area? (I've never done a dormer before!!)

sydthebeat

so are you using the heat pump as the main space AND water source?

are you inputting the HP as supplying all the DHW or 50%

are you calculating DHW HP efficiency using the formula in DEAP?

you can see your total solar heating input in the results page... please post.

I think your heat pump is whats letting you down, not the solar.

Patrickof

No, the heat pump/solar panel is only for the DHW. Space heat is a new boiler (mains gas).

The heat pump is integrated into the solar panel. see ************ for a spec on it. it sounds quite good, but the results BER wise are a bit disappointing. Methinks they'll be longer recouping their costs than they expect.

Not at the DEAP PC, will post in the morning.

edit:

no linking to product websites

sydthebeat

No7

There's virtually no technical details on the website.

sydthebeat

if the heat pump isnt supplying all your DHW then you need to apply the formula:
1 / [(50/spf)+0.5]

i still think you main issue i swith yoru heat pump... you get a reduced eficiency in DHW and you also have a 2.7 multiple as your primary energy conversion factor. Both of these work against the energy gains from the solar system.