Advice on energy efficient system please

[chrisreboot]

Hi all, it's my first post, so please be gentle!I currently have a standard gas combi boiler to supply my central heating and hot water.It's about 15-20 years old and I'm told about 70% efficient. So I am now in the process of looking at what the best replacement solution is.Add to the mix the fact that we have recently installed a solar PV system into the house which at times will over-produce energy.My current plan of thinking is to harvest that spare energy by putting it to use in heating water for us. This would involve having some kind of storage cylinder and immersion heater.This sounds a little like old school heating systems (which the house previously had before the airing cupboard had the water cylinder ripped out at the time the combi boiler was installed).However, I am thinking of the following system (and here's where I need critique from experts):1) Replace combi boiler with new more efficient condensing system boiler. (Not sure what I would need exactly, but we have a 4 bedroom house with one bathroom, and 6 kids to wash so our bathing hot water requirement is high!)2) Add a thermal store cylinder that would allow me to heat the water using a mixture of the gas boiler, and the immersion.3) To ensure best energy efficiency, I've seen on the market solar immersion switches that power the immersion when it detects that the Solar PV output is greater than the household consumption (i.e. diverts the excess power from going back to the grid), so the spare electricity I produce would go to heating the thermal store.I also very much like the idea of energy recovery, so something like the Gas Saver Product from Alpha Innovation. It looks good, but I guess that would have to be coupled with one of their own boilers.If there are any other similar pieces of kit out there that fit the bill I'd be happy to hear about them. Preferably an integrated system.Note: at present the solar PV installation is very new and I don't have the full data on over-prodcution to see if this plan is viable, so if anyone has any supporting evidence either way to this, again I'd be glad to hear about it. It could be that our spare output would not justify the installation. However, the fact that these products exist tells me there is mileage in this.I have no experience in this whatsoever, all I know is that I have spare power going to the grid that could lower my gas bill potentially.Am I shooting in the right direction with this kind of setup?Cheers,Chris

 

[Killy Bing]

Regarding a thermal store my knowledge is limited but it is just that, to store heat from multiple sources.
you would need an additional cylinder for your bathing water putting costs up further unless you have one which acts as a combi to give instant hot water but these are prone to scaling.

however it is ideal if you intend to add solid fuel, a heat pump or water based solar in the future.

the immersion idea is a good one but how big is the pv and what is the output?

as For the alpha gas saver it is a good idea but the parts for alpha boilers are considerably more.
the additional repair costs in the future will far outweigh money saved.

personally, unless you're going to stay in the house for life.

i would go for an intergas combi boiler with an unvented cylinder (my preference is oso ho****er super series or even better ACV cylinder)

Have the combi feed the kitchen tap for hot water
if you wish to add solar in the future get a cylinder with a second coil.

and insulate insulate insulate!!
have the floors up and insulate all hot pipework
upgrade loft insulation
look at cavity wall insulation
where cavity wall is not possible consider "dot and dab" insulated plaster board for those walls.

 

[efficiencyman]

Do you have more roof space for solar thermal ? If you do then a multiple coil cylinder could be heated for free or partly heated during the cooler months, ( I did that 23 years ago when my teenagers were at home, I reckon it`s paid for itself 4 times over )
In 2012 I fitted a 15 Kw heat pump to heat the house, under floor, Koi pond and pre heat the DHW very pleased with the performance. Needs a careful set up & control to obtain a good COP factor !
I would fit a condensing SYSTEM Boiler for storage cylinder top up and for heating ( as mine is, when in HYBRID mode if you fit a Heat Pump)
These are my points, Killy Bing has answered well, especially insulate everything.

 

[chris watkins]

What is the rated output from the PV set in watts, in full sun ?
I thought the Gas Saver was only for use with combi's & you were talking about having a system boiler ?
Welcome to the forum Chris.

 

[chrisreboot]

thanks for the feedback already guys!

So I'll try and answer the points in order. Since posting this earlier, I've taken other advice, and it may appear that perhaps this may not be the most obvious way to go, but I'll get back to that in a minute.

The PV system is 3.4 kwh output. I won't be adding solid fuel, but there is the possibility of adding solar thermal on the roof, but I have no experience of this as yet. We have no plans to move for a long time yet, so I'm prepared to invest for the long term.

Perhaps a cylinder with a second coil is a good shout so I can add solar thermal as well as power an immersion from PV.

Insulate is great advice. We need to lag pipes which is on the cards. We recently had a Green Deal assessment done, and have an EPC. Since then we have changed lights to low power/LEDs all round, and already had cavity wall and loft insulation. PV was next and has been in for 4 weeks now. Reducing the gas bill is the next target.

Not 100% on the Gas Saver being compatible with the system boiler, I have pinged the manufacturer to check.

I have a visit booked with a renewable energy fitter next week to see about boiler/cylinder options and also air source heat pumps and solar thermal. More research to do...!

 

[Worcester]

OK, here's some ideas (we install ALL renewable technologies except wind..) - you have a LARGE hot water demand, and depending upon wether you have to space to put large storage cylinders there are a couple of solutions

1)
Replace Combi with a high efficiency condensing gas boiler.
Add in unvented twin coil hot water cylinder to loft space if you've got it (keep your airing cupboard) - you'll need to have the pressure and flow checked to make sure that an unvented cylinder will work. based on the house occupancy you'll need a DHW cylinder of AT LEAST 6*45x2 = 540 litres. (45 litres per person, x 2 because you'll want a dedicated solar thermal element) - OR you could go to a twin tank set up - 2 x 250ltr - 500 ltrs in the loft is a LOT of cylinder = 600kg
Add in an 'ImmerSun' type device PV Water Heating, Solar Hot Water Switch and Controller Supplier in Lincolnshire, UK | immerSUN to the Immersion heater in the twin coil tank
Then you'll want at least 8m2 of solar thermal panels

OR: (my recommendation)
Use new high efficiency combi boiler that accepts pre-heated water. So you've got as much water as you could ever want.
Install a thermal store with a solar coil and immersion heater to capture the excess energy from the PV - ImmerSun as above.
Add in 8m2 of solar thermal panels (South or West facing - East gets the morning mist) (1 m2 / person)

Your chances are with that set up that the combi does very little from May - September (our heating is completely turned off in those months)

Example - there are variations (no drain back on the panels, unvented store etc ) this is to illustrate the basic configuration


ASHP waste of ££ if you're on mains gas .. (and we fit them )

 

[TBServices]

Baxi DuoTec Advance system combi with solar PV immersion heater in thermal store. Winning.

 

[TBServices]

http://www.baxiknowhow.co.uk/campaigns/heatsaver.htm

 

[TBServices]

And weather comp.

 

[Worcester]

Baxi DuoTec Advance system combi with solar PV immersion heater in thermal store. Winning.

Good solution, if he doesn't want to add thermal later..