Ideas about how to setup air heat pump, supported by PV's, for the highest cost efficiency during winter

[SteamyTea]

31 minutes ago, Gone West said:

What do you do with all the electricity in the summer when you don't need a large tank of hot water

Complain that we only get 5p/kWh for exporting it, instead of 50p/kWh.

[JohnMo]

2 hours ago, Gone West said:

What do you do with all the electricity in the summer when you don't need a large tank of hot water?

 

Fill it with cold water and circulate through the floor?

[Roger440]

3 hours ago, Gone West said:

What do you do with all the electricity in the summer when you don't need a large tank of hot water?

 

Nothing much i guess. I have no use for it.

[Roger440]

20 hours ago, Roger440 said:

I very much like the large tank idea.

 

Ive been looking at this, as i have, effectively unimited space for solar panels, and more or less, unlimited indoor space in the barn.

 

It much cheaper than batteries, And simpler. And no bunch of electronics to go wrong.

 

The question then is, do you use a heatpump to heat that water? As it will be circa 3 times more efficient than immersion.

 

Cost of solar panels at £100 a pop V the cost and complication of a heat pump.

 

If it works well enough, then i can not bother destroying the house to try and insulate it.

 

Idea needs proper numbers putting to it. Which is where i tend to fall down.

 

Sadly, a rough calculation suggests im dreaming.

 

Based on my oil consumption, im currently munching circa 70kWh per day if my calcs are right. Though that may not be the case..

 

And ive got a barn to heat part of by some means too.

 

 

[JamesPa]

16 hours ago, Roger440 said:

 

Sadly, a rough calculation suggests im dreaming.

 

Based on my oil consumption, im currently munching circa 70kWh per day if my calcs are right. Though that may not be the case..

 

And ive got a barn to heat part of by some means too.

 

 

Depends on your objective.  Remember 70kWh oil = 25kWh with an ashp.  Its unlikely you will get this amount from solar in deepest winter, but in the shoulder season you may well do so.  Presumably the barn has a large roof?

[SteamyTea]

44 minutes ago, JamesPa said:

Remember 70kWh oil = 25kWh with an ashp

Has the inefficiency of the oil burner been taken into account.

Could be closer to 50 to 55 kWh_th delivered.

So down to 20 or less needed from PV.

[Roger440]

58 minutes ago, SteamyTea said:

Has the inefficiency of the oil burner been taken into account.

Could be closer to 50 to 55 kWh_th delivered.

So down to 20 or less needed from PV.

 

I used 90% to allow for inefficency. On little basis other than that seems sort of right-ish.

 

20 would only apply with a HP of course.

 

To get 20 in mid winter, even if mounted vertically is going to be a massive array. 

 

The numbers people seem to be getting are all over the place, so hard to know.

 

Im keen to avoid batteries. Partly due to cost, but also moves me further away from DIY.

[SteamyTea]

1 minute ago, Roger440 said:

used 90% to allow for inefficency

Good luck getting that from an oil burner attached to a domestic central heating system.

You only need to stand by the flu and feel what is coming out.

[Roger440]

1 hour ago, JamesPa said:

Depends on your objective.  Remember 70kWh oil = 25kWh with an ashp.  Its unlikely you will get this amount from solar in deepest winter, but in the shoulder season you may well do so.  Presumably the barn has a large roof?

 

Yes, the barn has a 4000sqft roof. But siginificantly shaded and a shallow pitch, so not really much use. I do have a 4 acre field, the southern bounday of which has uninterrupted views of the sky.

 

I we thinking more along the line of JohnMo's arrangement of vertical panels to maximise winter production. (glossing over any planning issues!)

 

As said earlier, tons of power in summer is of little use to me, 

 

If i need to top up with the oil burner in the least productive periods, that not an much of an issue. It will be a massive oil consumption reduction either way.

 

Heating parts of the barn is a seperate issue project. Though potentially stil linked. Just to make life more difficult. That currently on resistance heating and makes my meter spin rather quick! I should resuurect by barn heating thread.

 

[Roger440]

4 minutes ago, SteamyTea said:

Good luck getting that from an oil burner attached to a domestic central heating system.

You only need to stand by the flu and feel what is coming out.

 

Thats what the internet suggests. What number do you think is realistic?

[SteamyTea]

Just now, Roger440 said:

 

Thats what the internet suggests. What number do you think is realistic?

I think once pumping costs and cycling is taken into account, 55 60 60%.

 

Simply way to find out, turn a room radiator off and put a fan heater in the same room, measure the differences.

[Gone West]

4 hours ago, Roger440 said:

I used 90% to allow for inefficency. On little basis other than that seems sort of right-ish.

My old oil fired Rayburn is at best 70% efficient. If I changed it for a new condensing oil boiler feeding a thermal store I should improve that to 90%. That alone would be a significant reduction in heating costs. If I managed to carry out all the insulation and air tightness improvements I want to do, I could more than halve the oil usage.

[SteamyTea]

1 hour ago, Gone West said:

My old oil fired Rayburn is at best 70% efficient. If I changed it for a new condensing oil boiler feeding a thermal store I should improve that to 90%

While newer oil burners can go into condensing mode, I think there may only be 1 or 2 that modulate.

This is why cycling them is so dreadful for efficiency.

They start up at full whack, a lot of energy is blown up the chimney, then, a few minutes later the return temperature rises above the condensing temperature, and before it can do anything about it, it has shut down.

There is a reason they don't put heat meters on combustion boilers, it would frighten customers.

[Roger440]

2 hours ago, Gone West said:

My old oil fired Rayburn is at best 70% efficient. If I changed it for a new condensing oil boiler feeding a thermal store I should improve that to 90%. That alone would be a significant reduction in heating costs. If I managed to carry out all the insulation and air tightness improvements I want to do, I could more than halve the oil usage.

It's a five year old condensing boiler so shouldn't be too bad.

 

I too could massively improve the house. Just makes no economic sense. I've sorted out all but one of the significant air leaks already. To sort the last one, I need to take the corner of the roof off!

[Roger440]

55 minutes ago, SteamyTea said:

While newer oil burners can go into condensing mode, I think there may only be 1 or 2 that modulate.

This is why cycling them is so dreadful for efficiency.

They start up at full whack, a lot of energy is blown up the chimney, then, a few minutes later the return temperature rises above the condensing temperature, and before it can do anything about it, it has shut down.

There is a reason they don't put heat meters on combustion boilers, it would frighten customers.

And the condensing temp on oil boiler is lower than gas ones too. When it's proper cold, it's ok, but in milder weather, cycling is unavoidable. So significant periods it's not condensing.

[JohnMo]

19 minutes ago, Roger440 said:

And the condensing temp on oil boiler is lower than gas ones too. When it's proper cold, it's ok, but in milder weather, cycling is unavoidable. So significant periods it's not condensing.

Not sure you are understanding condensing mode correctly.  An oil boiler goes into condensing mode when the return water temperature is below 47 deg.  Condensing is when the water vapour in the exhaust stream is converted from water vapour to water, the heat exchanger basically collects the latent heat and increased efficiency.

 

Nothing to do with cycling or not in hot or cold weather.

[Gone West]

From the Grant installation manual.

 

To achieve the maximum efficiency possible from the Grant Vortex boiler, the heating system should be designed to the following parameters:

RADIATORS:

• Flow temperature 70°C

• Return temperature 50°C

• Differential 20°C

Size radiators with a mean water temperature of 60°C.

Design system controls with programmable room thermostats or use weather compensating controls to maintain return temperatures below 55°C.

The use of a pipe thermostat is recommended to control the return temperature when using weather compensating controls.

 

! NOTE !

The boiler should not be allowed to operate with return temperatures of less than 40°C when the system is up to temperature.

 

[JohnMo]

24 minutes ago, Gone West said:

From the Grant installation manual.

 

To achieve the maximum efficiency possible from the Grant Vortex boiler, the heating system should be designed to the following parameters:

RADIATORS:

• Flow temperature 70°C

 

• Return temperature 50°C

 

• Differential 20°C

Size radiators with a mean water temperature of 60°C.

 

Design system controls with programmable room thermostats or use weather compensating controls to maintain return temperatures below 55°C.

The use of a pipe thermostat is recommended to control the return temperature when using weather compensating controls.

 

 

! NOTE !

 

The boiler should not be allowed to operate with return temperatures of less than 40°C when the system is up to temperature.

 

So although classed as a condensing boiler they are not really keen it being operated that way, with the advised baseline operating settings.

[sharpener]

56 minutes ago, Gone West said:

Design system controls with programmable room thermostats or use weather compensating controls to maintain return temperatures below 55°C.

The boiler should not be allowed to operate with return temperatures of less than 40°C when the system is up to temperature.

 

 

Conflicting requirements. Low enough to condense but not so low as to get corrosion.

I don't suppose many installations achieve a low enough flow to reliably get 20C drop across all radiators. So with a flow set to 70 it will probably not condense at all.

 

1 hour ago, Gone West said:

The use of a pipe thermostat is recommended to control the return temperature when using weather compensating controls.

 

There used to be a Danfoss aftermarket Boiler Energy Manager which would control a boiler to maintain the correct return temp for WC. Same principle, worked well on an Ideal Mexico, cut gas bill by 1/3.

[Roger440]

15 hours ago, JohnMo said:

Not sure you are understanding condensing mode correctly.  An oil boiler goes into condensing mode when the return water temperature is below 47 deg.  Condensing is when the water vapour in the exhaust stream is converted from water vapour to water, the heat exchanger basically collects the latent heat and increased efficiency.

 

Nothing to do with cycling or not in hot or cold weather.

 

Maybe didn't explain myself well.

 

When it's cold, the return temp is lower because more heat is dumped into the house.

 

At least that's what I've found with an IR thermometer on the return pipe. 

 

So when it's milder, I find I need to turn down the boiler temp if I want the return temp low enough.

 

Ie, manual weather comp. Not overly practical of course 

[Gone West]

6 hours ago, sharpener said:

I don't suppose many installations achieve a low enough flow to reliably get 20C drop across all radiators. So with a flow set to 70 it will probably not condense at all.

What would be the most reliable way of setting up an oil boiler and a thermal store so the boiler condenses most of the time. The radiators would be directly linked to the thermal store.

[sharpener]

Not sure what the purpose of your thermal store is, unlike electricity the oil is the same price day or night.

 

However assuming you can get reasonable stratification I would think the way would be to allow the rads to deplete the store until it is all at 45C assuming they will provide useful heat at that temp.

 

Then run the boiler at 70 to recharge the store until the return to the boiler rises to 50 or 55 and stop at that point which will ensure a good long condensing run.

[Gone West]

15 hours ago, sharpener said:

Not sure what the purpose of your thermal store is

It would be to allow me to run the oil boiler as efficiently as possible.

[SteamyTea]

16 minutes ago, Gone West said:

It would be to allow me to run the oil boiler as efficiently as possible.

Have to offset the standing losses, which may, or may not, be useful.

[Gone West]

1 minute ago, SteamyTea said:

Have to offset the standing losses, which may, or may not, be useful.

Yes that's one consideration of many, I think. Also, size and shape of the tank. Size, type and position of the heating coil. PHE or coil for DHW. The problem, when there are many variables, is knowing the effects of one of the variables on the others.