Heat Banks and Thermal Stores

[kipperman]

have just completed DIY install of new CH and water supply in major extension. Fitted a 250L heat bank from DPS ( heatweb.com).

What boiler is on it and what temperature is the store operating at?

I can't understand at all how a 'high efficiency' boiler can be expected to operate efficiently when connected to a tankful of water already at 75+ degrees!

Boiler is a Vokera Synergy 28e

I can see what you mean - but when there is a draw on the thermal store ( ie the heat exchanger is in operation), the temperature of the water in the store will of course drop as it gives up it's heat and therefore the return temperature from the internal heating coil will drop as it restores the water in the bank to its designated temperature ( I have it set to 70 degrees ). I can't see what is different in this scenario from any other hot water system ( such as vented or unvented system). The other point I would make is that as I understand it the energy used in heating hot water is relatively small compared to that used in heating the house, and therefore if there is a reduction in efficiency in the hot water system, it too will be relatively small.

One of the other major reasons for choosing the thermal store ( beyond DIY permissibility) is that we live in a bungalow- although we have now extended into the roof space. This would mean if I chose a conventional vented system I would have had extremely restricted space for a cold water store and very poor head for upstairs showers. Choosing a thermal store ( or an unvented system if I were qualified) means no pumps for our two showers with an associated cost saving) and a much simpler install. The DPS stores come with the option of having all the CH valves, programmers and wiring already in place- so fitting the store is simple.

The final point is that it works- extremely well. Mind you having lived in a mobile home with a 7kw electric shower for 4.5 months even a combi boiler would feel good at the moment

 

[HarryM]

Nige, I'm all for the cheapest option.

Is it a realistic proposition? Any problems with building control?

Would I have to cap off the chimney? Currently fitted with a chimney pot, and its a stone wall about 2 feet thick.

 

[croydoncorgi]

The other point I would make is that as I understand it the energy used in heating hot water is relatively small compared to that used in heating the house

Wrong assumption, unfortunately. The amount of energy (from gas or oil) required to heat a given volume of hot water in a cylinder to (say) 55 degrees will VARY according to what temperature a condensing boiler operates at. The boiler Flow temperature will also affect the recovery time of the cylinder (to go from cold back to hot).

If you run the boiler close to its maximum (usually about 80 degrees), the cylinder will recover quickly but the boiler will seldom if ever run in condensing mode. For this to happen, the Return temperature MUST be below 56 degrees. So it's a compromise between gaining the additional 10% or so of conversion efficiency (from energy in the fuel into 'useful heat') and waiting a bit longer for your water to reheat.

Unfortunately, not many boilers 'know' whether they are heating hot water or radiators, so the Flow temperature is effectively fixed at one compromise setting.

 

[Doctor Drivel]

The other point I would make is that as I understand it the energy used in heating hot water is relatively small compared to that used in heating the house

Wrong assumption, unfortunately. The amount of energy (from gas or oil) required to heat a given volume of hot water in a cylinder to (say) 55 degrees will VARY according to what temperature a condensing boiler operates at. The boiler Flow temperature will also affect the recovery time of the cylinder (to go from cold back to hot).

If you run the boiler close to its maximum (usually about 80 degrees), the cylinder will recover quickly but the boiler will seldom if ever run in condensing mode. For this to happen, the Return temperature MUST be below 56 degrees. So it's a compromise between gaining the additional 10% or so of conversion efficiency (from energy in the fuel into 'useful heat') and waiting a bit longer for your water to reheat.

Unfortunately, not many boilers 'know' whether they are heating hot water or radiators, so the Flow temperature is effectively fixed at one compromise setting.

You need to get to know more about thermal storage.

 

[chrishutt]

You need to check the date on posts before replying.

 

[Doctor Drivel]

You need to check the date on posts before replying.

It still does not detract from the point I was making.