Hot Water Advice (5 person house)

Anto318 · 27-05-2020 9:54am #1

Hi All,

I'm purchasing a house at the moment which was built in 2004. The house has a recently installed boiler (Ideal Logic Heat 24) but I have some questions that I hope you might be able to help with.

I'm moving from a new property where we have solar panels and during the summer months we'd have constant hot water. In the new property we don't have the same options.

There's 5 in our household with 2 adults and 3 teenagers so I'm concerned that in the new property our bills will go through the roof for hot water.

We're planning on doing some upgrades to the house before we move it (cavity wall pumping, attic insulation etc) and we're planning on changing out the bathrooms. Currently the showers are fitted with electric showers.

I'm looking for suggestions on what's the best approach with the upgrades. Would we install Solar PV with a diverter to a larger hot water tank (current tank is 200L) and replace the electric showers with mixer showers off the tank?

Any advise you can give would be appreciated. As I'm going from hot water Apr-Sept for free in my current house I'm nervous of getting a real spike in bills once we move into the new home.

Thanks in advance,
Anto318

John.G · 30-05-2020 3:19pm

Try a get a handle on the running costs assuming all hot water gas derived and assuming HW consumption @ 50 LPD/person at 40C, gas at €0.076/kwh and boiler efficiency at 80%. the annual HW energy required is, 50*5*365*(40-10)/860, 3183 kwh, energy input, 3183/80%, 3979 kwh, Cost, 3979*0.076, €302/annum.
Assume that solar thermal will give a minimum saving of half, = saving of €151/annum, very hard (if not impossible) to justify solar thermal installation on the above. Someone else can comment on solar PV.

roy rodgers · 03-06-2020 10:52am

Hi anto318.

What id the BER rating of the new house your looking to purchase?
Amd what what is your living arrangement likely to be? Will there be some one at home all day or not?

I be a big fan of solar pv in general. But it has to be sized in accordance to your living needs.
With solar pv the house electric needs will always be priority over heating water so if someone is at home during the days using appliances the solar pv generation will be what runs these appliances. Only when there is a surplus of electricity they your diverter will kick in the hot water switch and heat the water instead of exporting to the grid.
You would want to be looking at a bigger solar pv system if you want the hot water to be heated up as well as running electrical appliances, I'd be looking at a 4kw system without a battery the seai grant will only cover up too 2kw of 900 euro per kw thou.
As the teenagers move on your likely to be generating more electricity than usage than you could look at adding at battery to your system down the line.
Even at this size you will still need to heat water by gas too and if your getting attic and cavity insulation it be a good time to get your heating controls done too where you can separate the hot water from the radiators.
I'd get these measures done first as if you got the solar pv done first and the house wasnt better than a C2 BER rating seai will not pay out on the grant..
If the hot water cylinder is just a standard cylinder you might also need to replace this with a high performance cylinder.
Solar thermal could work here too as your current experience with it have been positive over the most of march to Sept.

Rough cost of solar pv for a 4kw system 6 to 8k depends of roof space.
Solar thermal 40 tubes 3.5 to 4.5k
300 liter hot water cylinder 1.5 to 2k
Heating controls 1 to 2k.

Hot Water Advice (5 person house)

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