Mixergy's new heat pump hot water cylinder (iHP)

Screwdriva

Looks like a no brainer for those using oil to heat hot water. Once the noise levels and ducting requirements become clearer, perhaps it will be a more mainstream product?

https://mixergy.co.uk/news-and-insights/introducing-mixergys-new-award-winning-heat-pump-cylinder-the-ihp/

ispookie666

Interesting development.  If anyone is installing ASHP from new should consider this. I'll give this a pass and stick to my oil boiler, wife and daughter love long showers 

Reed_Richards

This fast reheat process from Mixergy allows for a quick boost with more than twice the efficiency of a direct electric heating element. On the other hand, the system can opt for the highest system efficiency (COP ~3.5+) through whole cylinder heating via the boost divert valve.

Screwdriva said:

Looks like a no brainer for those using oil to heat hot water. Once the noise levels and ducting requirements become clearer, perhaps it will be a more mainstream product?

https://mixergy.co.uk/news-and-insights/introducing-mixergys-new-award-winning-heat-pump-cylinder-the-ihp/

Right at the moment oil is pretty cheap compared to electricity; I think you would need a better COP that 3.5 to be cost competitive (but feel free to provide the sums that show me wrong).  Oil needs to be a clear-cut winner, so what you save on running costs will pay back the installation cost.
    

Magnitio

The price of this might be an issue. I would guess at £2-3k based on their prices for other cylinders.

Screwdriva

Reed_Richards said:

Right at the moment oil is pretty cheap compared to electricity; I think you would need a better COP that 3.5 to be cost competitive (but feel free to provide the sums that show me wrong).  Oil needs to be a clear-cut winner, so what you save on running costs will pay back the installation cost.

I think oil has been quite volatile (and is a bit more inconvenient to use). When paired with Solar PV, this cylinder could cost much less to use.

I've asked Mixergy for specifications (especially noise emissions) and will share them. The other installer I recommend installs Libbi batteries and Mixergy cylinders and should be able to quote for it soon. 

Magnitio said:

The price of this might be an issue. I would guess at £2-3k based on their prices for other cylinders.

I believe they will price this close to the Valiant Arostore alternative.

orbit500

And where does this extract the heat from? The house, which you’ve paid 10p/kWh to heat?

Rodders53

Screwdriva said:

Looks like a no brainer for those using oil to heat hot water. 

To continue to use Kerosene oil to heat it. Current oil is circa 5.6 p per kWh so a COP of 4 (unlikely) would need leccy to be < 23 p/kWh to match todays price.  My last fill (November) was equivalent to 9p/kWh so 36p at cop of 4... 
It will never payback the cost to change for oil users. If they change to ASHP from oil then the current HW cylinder may work adequately or need an upgraded coil type... No need for a second HP atop the tank.

These are, I suspect, maybe a goer for all-electric flats to heat the water less expensively? But water heating isn't the biggest energy use item in the UK. That is space heating.

Also may I observe they only show it heating water to 50C --- OK Legionella will eventually die at that temperature, and is a sealed water system (from the mains) but it's sub-optimal in some situations.

orbit500 said:

And where does this extract the heat from? The house, which you’ve paid 10p/kWh to heat?

They duct the air in from/out to a wall nearby.  Hence a compressor motor and air movement fan (think of a mobile air conditioner).  Think noise.

Screwdriva

Rodders53 said:

To continue to use Kerosene oil to heat it. Current oil is circa 5.6 p per kWh so a COP of 4 (unlikely) would need leccy to be < 23 p/kWh to match todays price.  My last fill (November) was equivalent to 9p/kWh so 36p at cop of 4... 
It will never payback the cost to change for oil users. If they change to ASHP from oil then the current HW cylinder may work adequately or need an upgraded coil type... No need for a second HP atop the tank.

A few points in response

- Current kerosine oil price is 40% lower than a year ago. 

- Even on Octopus Flux, your incoming tariff is 20p, from 2-5am, which is the stated 3 hours needed to heat up hot water every night. This doesn't factor in PV export lowering the effective price per kWh further or any of the intelligent tariffs. 

- Decibel levels are pending but I'm told by my installer it is quieter than the AroStore+

- 90% of Legionella dies within 2 hours at 50 degrees.

- Claimed peak COP is 3.5, higher than any heat pump can heat hot water today, but I wonder if this can be improved by drawing warmer air from the attic.

I've asked them if they allow for gas central heating as a backup source. I find it very intuitive that the heat pump unit can be removed for service while keeping the cylinder plumbed. 

Reed_Richards

- Current electricity price (SVT) is 200% higher than two years ago.

- I have wondered about siting a heat pump in my attic.  The air inside my attic is warmer than the outside air but if I started drawing heat out of it that might change.  You need your attic to be "poorly" ventilated to have warmer air inside it but then to become well ventilated if the air temperature inside the attic approaches the temperature of the outside air.  So that might be another fan with differential temperature sensors.  I would like to feel that there is a way to recover "waste" heat lost to the attic but it's a complicated can of worms.  And taking heat out of the attic rather than from outside, will increase the rate of heat loss from my house

   

Grandad2b

Reed_Richards said:

- I have wondered about siting a heat pump in my attic.  The air inside my attic is warmer than the outside air but if I started drawing heat out of it that might change.  You need your attic to be "poorly" ventilated to have warmer air inside it but then to become well ventilated if the air temperature inside the attic approaches the temperature of the outside air.  So that might be another fan with differential temperature sensors.  I would like to feel that there is a way to recover "waste" heat lost to the attic but it's a complicated can of worms.  And taking heat out of the attic rather than from outside, will increase the rate of heat loss from my house

   

I don't know your house but I would guess the volume of air in the loft is smaller than the volume of the rest of the house. How long will it take to use the energy being 'stored' in the loft?

Reed_Richards

Grandad2b said:

I don't know your house but I would guess the volume of air in the loft is smaller than the volume of the rest of the house. How long will it take to use the energy being 'stored' in the loft?

It's a pitched roof that I can stand up in so the volume of the loft must be close to half the volume of the rest of the house. 

I looked it up and air has a heat capacity of 700 J per kg per K and water has a heat capacity of 4184 J per kg per K.  So heating a kg of water by 1 C would reduce the temperature of a kg of air by 6 C.  A kg of air occupies about 0.82 m3 and a kg of water occupies 1 litre.  So if you have a 250 l hot water tank and want to raise its temperature by 1 C you would need to reduce the temperature of 1225 m3 of air by 6 C.  If my roof is 2.5 m high at the apex then its average height is 1.25 m so I need a floor area of 980 m2 to have 1225 m3 of air in the loft.  I live in a bungalow and actually have about 200 m3 of floor area. 

So either I have done the calculation wrong or I've talked myself out of the idea of extracting heat from the loft on the basis that there isn't nearly enough.  I think I have also reasoned myself out of using an exhaust air heat pump.  Have I made a mistake?