The tragic reality of energy independence!

Martyn1981

70sbudgie said:

Martyn1981 said:

Lastly, I don't require 30kW of heating, certainly not for a long period, as combi's (mine is a 28kW), are sized to meet instantaneous hot water demand, not long term heating. 

This explains why when we replaced our 28kW combi boiler with a system boiler (and hw tank), we only needed a 24kW boiler. I had always wondered if I had remembered the size of the combi boiler wrong!

It's actually quite eye opening how important it is to consider heat loss first, before adding heat. I've grown up with the mantra that the first 3 things you do are insulate, insulate, insulate.

TBF, I'm actually pleasantly surprised having broken things down to a daily/hourly average. It's a bit of a shock.

Obviously you will get exceptional periods of cold sometimes, but even if I take a negative guestimate from that winter consumption I gave of 2,761kWh's, and suggest 2,000kWh's just for a really bad January, then that's 'only' a daily heating need of 64.5kWh's (if the GCH is 100% efficient, and none of the DHW heat is lost down the drain), or 2.7kW's constant. [For background we have a classic (translates as 'bog standard') 1930's 3-bed semi.] 

Always worth considering the huge amount of solar gain we get through windows, plus body heat (humans and pets) and all of the leccy consumption, which also translates into heat. Someone once suggested that insulation might (as an example) half your heat loss, but reduce direct heating by 67%, if indirect heating previously provided 25%:

Heating requirement was 100 units, made up of 25 units indirect and 75 units direct such as GCH.
Reduce the heat loss by 50%, and you now only need 25 direct units since the other forms of indirect heating remain.

Sort of the idea behind Passivhaus standards which try to minimise heating via minimising heat loss.

Screwdriva

This is the first time I've heard a minister mention the words Tidal energy & baseload in the same sentence! 

https://www.youtube.com/watch?v=6mrq180Vqg0

diystarter7

I am stupid and or thick but I still don't have an idea of hw much approx electricity is used when I turn on the CH and or hot water via the combi boiler. It's a Valiant Ecotec 828 or something like that.

is the pump on most of the time when cH is on and on all of the time when we run hot water?

Does the pump use as much electric as a 100watt bulb etc?

Thanks again

Martyn1981

Hiya, the pump is on to move the water around the radiators etc, so yes, it's running pretty much all the time your heating is running.

Regarding energy consumption, yes, you are spot on, roughly 100W's is a reasonable est. Bigger boilers, especially those designed to provide for more radiators, and perhaps more floors will have bigger ranges, but ~100Ws will do.

michaels

Martyn1981 said:

Hiya, the pump is on to move the water around the radiators etc, so yes, it's running pretty much all the time your heating is running.

Regarding energy consumption, yes, you are spot on, roughly 100W's is a reasonable est. Bigger boilers, especially those designed to provide for more radiators, and perhaps more floors will have bigger ranges, but ~100Ws will do.

I thought they were now much more efficient due to an EU directive?  Of course most existing ones will be the old higher energy ones

diystarter7

Martyn1981 said:

Hiya, the pump is on to move the water around the radiators etc, so yes, it's running pretty much all the time your heating is running.

Regarding energy consumption, yes, you are spot on, roughly 100W's is a reasonable est. Bigger boilers, especially those designed to provide for more radiators, and perhaps more floors will have bigger ranges, but ~100Ws will do.

Many thanks.

phsci

michaels said:

I thought they were now much more efficient due to an EU directive?  Of course most existing ones will be the old higher energy ones

I think so too. My 4 or 5 years old Grundfos Alpha2 is rated at 22 Watts max, modulating down to 5 Watts, but they last for many years so understand the comment about older ones.

Reed_Richards

Screwdriva said:

 A really good modulation ratio (2 kWh at max modulation) translates to 98% efficiency. I

The ability to modulate down to very small power outputs will reduce cycling so you can run continuously at a low output water temperature rather than cycling on and off at a higher water temperature when the demand for heat is low.  But the biggest economies come when its cold outside and the demand for heat is high.  The main factor that translates into 98% efficiency when you need it most is the low output water temperature you will use; don't lose sight of that.    

Screwdriva

Reed_Richards said:

The ability to modulate down to very small power outputs will reduce cycling so you can run continuously at a low output water temperature rather than cycling on and off at a higher water temperature when the demand for heat is low.  But the biggest economies come when its cold outside and the demand for heat is high.  The main factor that translates into 98% efficiency when you need it most is the low output water temperature you will use; don't lose sight of that.    

We designed the entire system to take advantage of the lower output water temperature. UFH at <35 degrees. Oversized rads at <55 degrees. DHW Tank at 50 degrees.

Reed_Richards

Screwdriva said:

Reed_Richards said:

The ability to modulate down to very small power outputs will reduce cycling so you can run continuously at a low output water temperature rather than cycling on and off at a higher water temperature when the demand for heat is low.  But the biggest economies come when its cold outside and the demand for heat is high.  The main factor that translates into 98% efficiency when you need it most is the low output water temperature you will use; don't lose sight of that.    

We designed the entire system to take advantage of the lower output water temperature. UFH at <35 degrees. Oversized rads at <55 degrees. DHW Tank at 50 degrees.

Yes, and that is what will get you close to your 98% efficiency.

Modulation down to 2 kW is only necessary when your heating demand is 2 kW.  That's 48 kWh per day (or less if the heating is off at night).  In my house 48 kWh per day would have been about my average heat & HW energy usage in April this year and  mid October to mid November last year(based on my electricity use and assuming I got a CoP of 3).