Anyone know much about setting up ASHP?

[cheezemonkhai]

1 hour ago, PetrolDave said:

I think the cost of running heat pumps (as well as the cost of swapping from gas fired boilers with the associated upsizing of radiators) is deliberately being ignored and/or understated.

 

This could be a big 'banana skin' for the 'green heating' movement IMHO.

 

We tried to get a water source heatpump, but the water extraction and return rules and licence costs per year are more than our gas bill (Even at todays prices).

Without those, you have to have planning to put radiators into the river/canal and the person responsible for the watercourse have a paddy.

 

Add in the cost of running air source or anything which suffers from the cold (below 7 degrees input temperatures) and then it's really not worth it.

That completely ignores the costs of converting the house to underfloor heating throughout, or at the very least to underfloor on the ground and low temperature radiators upstairs.

 

I think when we looked at it, the real cost was closer to 30-40k, which isn't really what you want to pay for higher bills.

If the cost was about the same as a gas boiler (all in) and it cost about the same to a little bit more, then I might be interested, but the £5k bribe, payed back in electric taxes over the next few years makes the whole thing pointless.

 

As you say, a big banana skin, because people want to, but if early adopters tell everyone it's expensive, then people will stay with what they know. I'd far rather keep 30k in the bank and suck up a high gas bill than drop 30k and pay for an even higher electric bill 😞

Edited 12 April, 2022 by cheezemonkhai

[Aspman]

We reckon we’ll use about 20-25000 kWh per year. Makes us laugh (bitterly) when we see the increases measured against and average use of about 6000.

 

 I’ll definitely be looking into solar/wind plus battery. But we need to balance that against thinking if we’re going to stay in this properly long enough to get anyway close to a ROI. 
 

we can’t go big on wind to take advantage of one of our problems since anything big enough will need planning which will be denied since we’re close to an rspb reserve. 

[fabdavrav]

On 11/04/2022 at 20:50, Aspman said:

 And I’m sure my ashp with its claimed 300% efficiency over gas doesn’t hit this figure when it’s -2C.

 

 

 

What make/model is your ASHP?...I'll have a look at the specs..

 

On 12/04/2022 at 10:24, cheezemonkhai said:

 

Of course gas isn't 100% efficient, but even at a relatively low 80%, for every 100kWh of "heat output" that's about £12 of gas at 9p/kWh vs £20 of electric @40p/kWh. It's closer with electric at 28p/kWh, at £14 but still not cheaper.

 

 

My current system I designed & installed in 2009yr (based on an older 1993yr system design which was way ahead of its time) Max demand of heating is 13.7kW (house heat loss) & max demand of hot water is 24kW coil in tank:-

 

WB Greenstar 24kW town gas boiler = SEDBUK rating of 90.2% efficiency, electrical consumption for the basic controls & ignitors (no pumps or timers in boiler casing) = 50W

GF Alpha pump heating circuit = max. electrical consumption is 45W, never seen it above 18W at full heating demand.

GF Alpha pump boiler shunt = max. electrical consumption is 32W, never seen it above 16W at full heating demand.

Siemens main remixer valve = max. electrical consumption is 3W

Siemens main controller = max. electrical consumption is 9W

HS Megaflow (170lt 24kW) Indirect HWT valve = max. electrical consumption is 6W

 

So basically my heating system at full tilt in cold weather & max demand consumes no more than 102W of electricity per/hr....& output 24kW of heat & it can ramp down to its minimum output of 8kW heat.

 

In fact it switches on & off when it needs to as it has external temp sensors on the north side of the house, & a remix valve to reuse the heating circuit return water before it gets back to the boiler. Extremely efficient for a 26yrs old design!

Edited 13 April, 2022 by fabdavrav

[Aspman]

https://www.grantuk.com/product-list/air-source-heat-pumps/r32/

[fabdavrav]

On 13/04/2022 at 16:01, Aspman said:

https://www.grantuk.com/product-list/air-source-heat-pumps/r32/

 

Which one??

 

Looking at the spec sheets there is 6, 10, 13, & 17kW.

 

The 17kW with outside air at +7C & creating a heating water flow temp of 55C gives you 15.3kW of heat. However, to do this it consumes 4.86kW of electricity. Therefore giving you 214% more output than input.

 

The 17kW with outside air at +7C & creating a heating water flow temp of 35C gives you 18kW of heat. However, to do this it consumes 3.76kW of electricity. Therefore giving you 378% more output than input.

 

Having looked in their "data sheet" this states other info not in their other documents:- the stated "max running current" is 25.3A & presumably at 230ACV then thats 5.81kW...which is greater than the above 4.86kW, & obviously efficiency will drop further..

 

Previously I had mentioned that older heating systems the rads were sized at delta 60C..& that for ASHP the rads are mainly sized at delta 30C.

 

Delta 30C is the max flow temp at 55C, the return temp at 45C & the room temp at 20C. 

 

Therefore you will only get a max of 214% under these conditions.

 

To use a max flow temp of 35C, which is delta 10C (35C flow, 25C return, 20C room)....& the rads would have to be HUGE!!!

 

Then you have the problem of hot water!

You need to have the flow temp of the "heating water" at least +10C greater than the required hot water temp in the tank. Therefore if the hot water in the tank is set to 50C the flow temp for the coil needs to be 60C. With the flow set to 55C max this will give you 45C hot water.

 

A flow temp of 35C will give you 25C...this is "warm"..& you'll have problems with legionella's in the tank etc..

 

By the way what hot water tank do you have??

 

Greenwashing!!

 

 

Edited 15 April, 2022 by fabdavrav
clarity

[fabdavrav]

On 05/04/2022 at 11:16, Aspman said:

 

• Keep the water temperature lowish (50) but make sure there is a boost to 60 in there to kill of the nasties

Not sure what the settign is here but I'd say our hw is not excessively scalding nor is there a huge amount of it. Enough for a couple of showers that's all. HW charges for 2hr in the morning and 1hr in the afternoon and the heating curcuits close during those periods. I

•  

 

 

Had another look at the installer manual for your ASHP.

 

grant-aerona-r32-installer-uk-doc-0136-rev-2-0-september-2020.pdf (grantuk.com)

 

I take it you also had the matching DHW tank fitted???

 

It seems that when there is DHW demand your ASHP automatically sets itself to the 55C flow setting, regardless of your setting for the heating (page 20)

 

Now this is still not enough to adequately kill of legionella....so they make a "DHW boost" kit..basically an electric immersion heater for their tank which takes the temp upto 60C...was this also fitted???

 

I would also look at the setting codes for the ASHP...ideally it should be set for weather compensation (pg39)..& also look at the pump output functions (pg41) as a low flow rate causes heating problems..

 

Personally it should do the DHW & heating all ok ...IF its been set up correctly..& many so called installers don't set up the controllers properly....

[Aspman]

On 14/04/2022 at 09:11, fabdavrav said:

 

 

Had another look at the installer manual for your ASHP.

 

grant-aerona-r32-installer-uk-doc-0136-rev-2-0-september-2020.pdf (grantuk.com)

 

I take it you also had the matching DHW tank fitted???

 

There is a large tank in attick

 

 

On 14/04/2022 at 09:11, fabdavrav said:

 

It seems that when there is DHW demand your ASHP automatically sets itself to the 55C flow setting, regardless of your setting for the heating (page 20)

 

Yep, we schedule the heating to go off during hw demand

 

On 14/04/2022 at 09:11, fabdavrav said:

 

Now this is still not enough to adequately kill of legionella....so they make a "DHW boost" kit..basically an electric immersion heater for their tank which takes the temp upto 60C...was this also fitted???

 

Specifically don't know but there is an emersion within the tank

 

On 14/04/2022 at 09:11, fabdavrav said:

 

I would also look at the setting codes for the ASHP...ideally it should be set for weather compensation (pg39)..& also look at the pump output functions (pg41) as a low flow rate causes heating problems..

 

Past what I know tbh. It's due a service in August, might try to pick the brain of the servicer (plumber?).

 

On 14/04/2022 at 09:11, fabdavrav said:

 

Personally it should do the DHW & heating all ok ...IF its been set up correctly..& many so called installers don't set up the controllers properly....

 

[EnterName]

I hope you've got this sorted now, because it looks like high energy bills are going to be with us for a bit.