The tragic reality of energy independence!

QrizB

Mikeyboy01443 said:

So why are export prices so high at the moment?

Because we're burning gas to generate it, and gas is expensive.

Screwdriva

We seem to have overindexed on wind, with insufficient emphasis placed on solar and hydroelectric. If we spent the money we do on Oil and gas research on tidal energy, we'd be an energy exporter! 

diystarter7

gazapc said:

diystarter7 said:

I read somewhere that combi boilers use a lot more electricity than I believed.  However, I'm still guessing that turning on gas combi heating has gone up but nowhere close to electric prices am I right?

We have those heat control valves on all rads bar one and we turn almost all of them down to the lowest setting other than the sitting room, landing, hall and bathroom.

Am I right re combi boiler and use of electric?

My Worcester combi uses a few Watts in standby and ~180 Watts when alight, mainly I imagine for the pump.

Why do you think combi boilers use lots of electric?

"alight" as in heating the rad and or hot water? If so that is a lot of electric being used and I read correctly. I wrongly assume that combi boilers hardly used any electric.

thevilla

diystarter7 said:

gazapc said:

diystarter7 said:

I read somewhere that combi boilers use a lot more electricity than I believed.  However, I'm still guessing that turning on gas combi heating has gone up but nowhere close to electric prices am I right?

We have those heat control valves on all rads bar one and we turn almost all of them down to the lowest setting other than the sitting room, landing, hall and bathroom.

Am I right re combi boiler and use of electric?

My Worcester combi uses a few Watts in standby and ~180 Watts when alight, mainly I imagine for the pump.

Why do you think combi boilers use lots of electric?

"alight" as in heating the rad and or hot water? If so that is a lot of electric being used and I read correctly. I wrongly assume that combi boilers hardly used any electric.

All central heating systems need a pump. A combi boiler tends to incorporate that pump but its not additional cost.    I think it is known as parasitic drain. 180 Watts compared to up to, say 18kw (max) of gas usage is negligible.

Coastalwatch

All central heating systems need a pump. A combi boiler tends to incorporate that pump but its not additional cost.    I think it is known as parasitic drain. 180 Watts compared to up to, say 18kw (max) of gas usage is negligible.

Yes, very true.

 Although, as my installer pointed out, multiply that by a factor of four when driving an A2A heat pump and you would get 720watts of heat all the time it is running.

Couple this together with efficiency losses in a GCH system and the cost of running an A2A heat pump is similar to heating by gas.

Martyn1981

Coastalwatch said:

All central heating systems need a pump. A combi boiler tends to incorporate that pump but its not additional cost.    I think it is known as parasitic drain. 180 Watts compared to up to, say 18kw (max) of gas usage is negligible.

Yes, very true.

 Although, as my installer pointed out, multiply that by a factor of four when driving an A2A heat pump and you would get 720watts of heat all the time it is running.

Couple this together with efficiency losses in a GCH system and the cost of running an A2A heat pump is similar to heating by gas.

I've been using that rule for a couple of years now when its borderline to put the GCH on, or the small A/C unit when PV generation is low. Our GCH pump, depending on the speed (1 to 3) runs at 80W to 140W (I seem to recall), so even if importing a small amount of leccy, I think the heat pump is better.

As for COP, I don't know if 4 is fair, but these will be daytime hours in the shoulder months, so outside temps won't be very low, so I feel 3 to 4 is reasonable for the COP.

Just to say, these thoughts and ponderings were based on old gas and leccy prices, before we entered the upside down.

Grumpy_chap

Coastalwatch said:

All central heating systems need a pump. A combi boiler tends to incorporate that pump but its not additional cost.    I think it is known as parasitic drain. 180 Watts compared to up to, say 18kw (max) of gas usage is negligible.

Yes, very true.

 Although, as my installer pointed out, multiply that by a factor of four when driving an A2A heat pump and you would get 720watts of heat all the time it is running.

Couple this together with efficiency losses in a GCH system and the cost of running an A2A heat pump is similar to heating by gas.

Martyn1981 said:

I've been using that rule for a couple of years now when its borderline to put the GCH on, or the small A/C unit when PV generation is low. Our GCH pump, depending on the speed (1 to 3) runs at 80W to 140W (I seem to recall), so even if importing a small amount of leccy, I think the heat pump is better.

As for COP, I don't know if 4 is fair, but these will be daytime hours in the shoulder months, so outside temps won't be very low, so I feel 3 to 4 is reasonable for the COP.

Just to say, these thoughts and ponderings were based on old gas and leccy prices, before we entered the upside down.

Perhaps I am being decidedly stupid or really misunderstanding something, but this does not seem to work in my understanding.

When the gas boiler is on, there is a circulation pump drawing, say, 200 W.  At CoP 4, ASHP could achieve heating input to the house of 800 W.
BUT, when the boiler is running, it is putting out, say, 30kW of heat to either water or space heating.
Turning off the boiler and using the ASHP instead of the circulation pump is going to leave the house very cold with a heating deficit of 29kW (in fact the 1 kW of ASHP heating may be less than the losses from the house).

I could see this could work if only operating the boiler for hot water and willing to wait for the tank to heat up, but probably too low if using a combi boiler as the flow of hot water too little.

As I said, it does not make sense as I have understood it.  One of the explanations is clearly incorrect.  

Martyn1981

Grumpy_chap said:

Coastalwatch said:

All central heating systems need a pump. A combi boiler tends to incorporate that pump but its not additional cost.    I think it is known as parasitic drain. 180 Watts compared to up to, say 18kw (max) of gas usage is negligible.

Yes, very true.

 Although, as my installer pointed out, multiply that by a factor of four when driving an A2A heat pump and you would get 720watts of heat all the time it is running.

Couple this together with efficiency losses in a GCH system and the cost of running an A2A heat pump is similar to heating by gas.

Martyn1981 said:

I've been using that rule for a couple of years now when its borderline to put the GCH on, or the small A/C unit when PV generation is low. Our GCH pump, depending on the speed (1 to 3) runs at 80W to 140W (I seem to recall), so even if importing a small amount of leccy, I think the heat pump is better.

As for COP, I don't know if 4 is fair, but these will be daytime hours in the shoulder months, so outside temps won't be very low, so I feel 3 to 4 is reasonable for the COP.

Just to say, these thoughts and ponderings were based on old gas and leccy prices, before we entered the upside down.

Perhaps I am being decidedly stupid or really misunderstanding something, but this does not seem to work in my understanding.

When the gas boiler is on, there is a circulation pump drawing, say, 200 W.  At CoP 4, ASHP could achieve heating input to the house of 800 W.
BUT, when the boiler is running, it is putting out, say, 30kW of heat to either water or space heating.
Turning off the boiler and using the ASHP instead of the circulation pump is going to leave the house very cold with a heating deficit of 29kW (in fact the 1 kW of ASHP heating may be less than the losses from the house).

I could see this could work if only operating the boiler for hot water and willing to wait for the tank to heat up, but probably too low if using a combi boiler as the flow of hot water too little.

As I said, it does not make sense as I have understood it.  One of the explanations is clearly incorrect.  

You don't need all of the power of the GCH "when it's borderline".

Also 'when it's borderline' we are talking about importing a bit of leccy to run a 2.5kW or 3.5kW HP (not 1kW) as PV gen isn't (in the example given) covering all of it. At that point, it's worth considering that opting for the GCH will consume gas and a small amount of leccy.

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. In the most recent Dec - Feb (and for HP shoulder months, when things are 'borderline' it's really early Q2 and late Q3/early Q4 we are talking about) we consumed approx 2,761kWh's of gas, for GCH, DHW and cooking (oven) or on average 30.68kWh's per day, or 1.3kW per hour (so to speak).

Edit - If it helps, for this year's early shoulder months (Mch-May), our gas consumption for heating, water and cooking was ~759kWh, or 8.25kWh per day, or 0.34kW per hour. This does include some A2A heating from leccy.

Screwdriva

Martyn1981 said:

You don't need all of the power of the GCH "when it's borderline".

Totally agree - this is why we went with the 19 kW Viessmann 200-W System boiler. A really good modulation ratio (2 kWh at max modulation) translates to 98% efficiency. It will still need power to run its pump but this ultra lean burn capability should see a dramatic reduction in gas consumption. Only 3 months before this is tested out in real life

70sbudgie

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!