Air source heat pumps

[Steve Skelton 1Participant @steveskelton1]

Simon, you would definitely need batteries, as in the winter, you are unlikely to get sufficient power from the panels to drive an ASHP. You would need at least 10kWhr of battery to give you a sensible running time before depletion of the batteries.

Steve

[David JuppParticipant @davidjupp51506]

I have ASHP and solar panels and nominally 10kWh of storage (in winter more storage would be good).

Unless you specify it – most solar/battery installs won’t provide power during a power cut.  To do that you’ll need extra equipment to handle the changeover (at extra cost), and most likely an additional local earth connection.

The installer I used said if grid is reliable at your location, then it’s not worth the extra costs – in areas supplied by overhead lines, it could well be worth spending the extra.

[Steve Skelton 1]

On Steve Skelton 1 Said:

Simon, you would definitely need batteries, as in the winter, you are unlikely to get sufficient power from the panels to drive an ASHP. You would need at least 10kWhr of battery to give you a sensible running time before depletion of the batteries.

Steve

Where would the power to charge the batteries come from?   In the winter I would suggest 10kWhr a good week from the panels.

[Steve Skelton 1Participant @steveskelton1]

John, we would charge the batteries up from the grid using an off peak tariff. We currently only pay 7p per kWhr for 6 hours overnight so we charge the car, run the dishwasher and dryer at night along with anything else that has a high power consumption. There are a number of special tariffs that charge less at certain times of the day.

Steve

[John MC]

On John MC Said:

On Steve Skelton 1 Said:

Simon, you would definitely need batteries, as in the winter, you are unlikely to get sufficient power from the panels to drive an ASHP. You would need at least 10kWhr of battery to give you a sensible running time before depletion of the batteries.

Steve

Where would the power to charge the batteries come from?   In the winter I would suggest 10kWhr a good week from the panels.

I am based rather further south than most of the forum, some 40kms north of Marseille, so we get a bit more sunlight during winter – and nearly 5000sqm to install panels on the ground.

Still trying to get a feel for what would work for us, what wouldn’t….not clear and we seem to have as many cowboys this side of the Channel as you do!

 

[noel shelleyParticipant @noelshelley55608]

An interesting point is how do you convert DC to an acceptable 50 c/s Without the grids stable 50c/s as a starting point – in some cases you can’t ! So when the grid goes down the wind and solar may go with it – NOT so clever ? Our grid system is very fragile and could easily be taken down. Noel.

[noel shelley]

On noel shelley Said:

An interesting point is how do you convert DC to an acceptable 50 c/s Without the grids stable 50c/s as a starting point – in some cases you can’t ! So when the grid goes down the wind and solar may go with it – NOT so clever ? Our grid system is very fragile and could easily be taken down. Noel.

Lots of problems in power supply, but this isn’t one of them.

Firstly, mains frequency isn’t particularly stable, see Gridwatch.  When I started typing this the UK frequency had varied during the previous 10 minutes from 49.827Hz to 50.145Hz, average: 49.995Hz.  Frequency is deliberately varied by the supplier as a way of managing demand, and it also is recognised, within limits, that the supplier cannot maintain frequency exactly, irrespective of the load.

Secondly, electronics can easily produce 50Hz orders of magnitude more stable than the mains.  Not difficult to do in the home for a few pounds, and it’s quite fun to monitor just how far off 50Hz the mains is at any given moment.

Thirdly, I can’t think of a case in which a 50Hz source depends on the grid for frequency.   Noel may be thinking of phase,  but sorting that out isn’t rocket science either.

My ancient microwave oven contains the worst clock I still use.  It counts pulses off the mains…

Dave

 

[Steve Skelton 1]

On Steve Skelton 1 Said:

John, we would charge the batteries up from the grid using an off peak tariff. We currently only pay 7p per kWhr for 6 hours overnight so we charge the car, run the dishwasher and dryer at night along with anything else that has a high power consumption. There are a number of special tariffs that charge less at certain times of the day.

Steve

I guessed it would be doing that, I do the same with a car, washing machine, dishwasher and occasionally a small heat treatment furnace.  I’ve considered a battery to go with my solar panels.  Problem is that the cost of the battery and installation will pay for a lot of grid electricity, off peak or otherwise.  I last looked at getting a battery a couple of years ago.  Assuming  ten tears life for the battery it would be unlikely I would cover the cost of them in that period.

Battery tech is moving forward at quite a rate, I watch the “market” with interest.  I’m sure batteries will become financially viable, for me, sooner rather than later.  Likewise heat pump tech is advancing rapidly, watching with interest.

One problem I’ve had with researching and buying PV’s and researching batteries and heat pumps is the evangelical nature of owners of this tech.  Trying to get realistic figures with regard to cost is not easy.  I seen some very extravagant claims, solar panels that reduce the electric bill by some 75% and so on.  Much the same for batteries and heat pumps.  Sifting through the available information takes quite a time!

 

 

[Steve Skelton 1]

On Steve Skelton 1 Said:

John, we would charge the batteries up from the grid using an off peak tariff. We currently only pay 7p per kWhr for 6 hours overnight so we charge the car, run the dishwasher and dryer at night along with anything else that has a high power consumption. There are a number of special tariffs that charge less at certain times of the day.

Steve

I guessed it would be doing that, I do the same with a car, washing machine, dishwasher and occasionally a small heat treatment furnace.  I’ve considered a battery to go with my solar panels.  Problem is that the cost of the battery and installation will pay for a lot of grid electricity, off peak or otherwise.  I last looked at getting a battery a couple of years ago.  Assuming  ten tears life for the battery it would be unlikely I would cover the cost of them in that period.

Battery tech is moving forward at quite a rate, I watch the “market” with interest.  I’m sure batteries will become financially viable, for me, sooner rather than later.  Likewise heat pump tech is advancing rapidly, watching with interest.

One problem I’ve had with researching and buying PV’s and researching batteries and heat pumps is the evangelical nature of owners of this tech.  Trying to get realistic figures with regard to cost is not easy.  I seen some very extravagant claims, solar panels that reduce the electric bill by some 90% and so on.  Much the same for batteries and heat pumps.  Sifting through the available information takes quite a time!

 

 

[pmm1Participant @pmm1]

I have a 6kW ground source heat pump – installed 2010.

 

The house, a converted threshing barn, was designed with a heat pump in mind.

 

The walls are basically 18” stone, 2” gap, 8” closed cell insulation, 1”gap (to facilitate wiring) and plasterboard, with double or triple glazed windows according to size.

 

A warm roof is fitted with insulation similar to the walls.

 

The downstairs floor is insulated.

 

Underfloor heating is fitted, both upstairs and down, with stone flooring downstairs and low tog carpets upstairs.

 

The ground source is 2 off 200 metre U shaped loops laid at least 2 metres deep in the field in front of the house. The field conveniently slopes down away from the house so the pipes were laid in sand with a constant gradient so as not to allow any air traps to occur.

 

The heat pump is installed in an outhouse so noise is not a problem.

 

The heat pump works on a 3 degree differential and the lowest temperature in the output pipe is about 4 degrees C in winter, so there is not any significant surface cooling due to the heat pump.

 

The heat pump works very well, but is usually only used to produce hot water (52 degrees) as the house is usually heated using a 6kW wood burning stove (as I have a near inexhaustible supply of hardwood logs).

 

The heat pump soft start module failed during Covid and it took about 8 months to acquire an (upgraded) replacement which, when fitted showed the compressor had failed and killed the soft start module, which explained why the module had been upgraded.

 

The local heat pump installers said they only installed and did not repair. They did, however, point me to a local firm who maintain commercial refrigerators who had a suitable unit in stock and soon fitted it.

 

So, for any heat pump compressor failure look to commercial fridge repairers to get a replacement compressor.

 

Paul

[BazyleParticipant @bazyle]

Is the 6kW input or output?

[pmm1Participant @pmm1]

6kW is the rated output

Paul

[duncan webster 1Participant @duncanwebster1]

Manchester science museum have installed a ground source heat pump but drilled down 135 metres to an aquifer as the heat source. This sounds sensible. Friend of mine has a house backing onto a biggish river. I wonder if the powers that be would notice if he diverted some of the flow.

They have also installed electric fired boiler to run the steam engines. This doesn’t sound as sensible, CCGT system is 60% efficient, whereas a gas fired boiler can be higher. Whichever, I hope the condenser cooling water is used by the heat pump. Got to be warmer than groundwater

[Martin KyteParticipant @martinkyte99762]

Significant gains can be made when large new builds have green tech designed in. Our new Lab opened in 2013 with 4 deep bore wells to service the heat pumps.

“The building is glass-clad, providing a light and spacious design. Heat build-up is reduced by automatic venetian blinds, between the standard double glazing and an outer glass skin. Other energy-saving features include heat recovery wheels that exchange energy between outgoing and incoming air, a ground source heat pump, and automatic control of lights to reduce intensity when daylight is available.”

The heat exchanger wheels achieve a typical 5 to 6 degree temperature change between incoming and exhaust air in winter which significantly reduced the heating demands. The Lab is a rock solid 21 degrees all year and I am convinced that staff actually choose to come in during heatwaves even if they would normally have the day off.!

Our electricity bill is still over a million quid.

https://www2.mrc-lmb.cam.ac.uk/about-lmb/building-and-facilities/

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