Should I or Shouldn't I ASHP?

[Nickfromwales]

Anybody want to have a stab at how long an ASHP will last, vs a good quality gas boiler?

 

This also needs to be factored in. 

[JohnMo]

About the same. ASHP shouldn't last as long as good fridge. But technically a heat pump produced today will be over taken efficiency wise every few years.

 

A poor boiler or heat pump install, is unlikely to last a a good one. So many variables.

Edited Friday at 11:15 by JohnMo

[Beelbeebub]

If you aren't bothered about claiming the grant then you could install a muktisplit A2A heatpump

 

This would give you cooling in the summer and leave the gas boiler for water and backup heating in winter. (summer water could be immersion heater from PV?) 

 

You haven't mentioned if you have a gas hob - factor that cost in if you want to get rid of gas altogether. 

[Oz07]

1 hour ago, JohnMo said:

About the same. ASHP shouldn't last as long as good fridge. But technically a heat pump produced today will be over taken efficiency wise every few years.

 

A poor boiler or heat pump install, is unlikely to last a a good one. So many variables.

Are heat pump warranties 10 years or more like a boiler? Genuine question I've never looked in to them

[Michael_S]

Suppose the heat pump gets a cop of 4 (not impossible given the low flow temps you are already operating at)

 

14.3k gas usage at 5.5p per kwh costs £786pa

14.3kwh gas input at 95% efficacy gas boiler divided by a cop of 4 at 7p per unit off peak rate using battery timeshift costs £238pa

 

In theory your heat pump install should be cheap, only need a small unit (6kw?) and only change to plumbing might be to replace the hot water tank with a large coil one and hopefully your battery would be big enough to timeshift your total demand even on the coldest days?  Risk is that the new govt plan to prioritise batteries may lead to a reduction in the potential savings from timeshifting due to increased arbitrage.

[JohnMo]

1 minute ago, Michael_S said:

Suppose the heat pump gets a cop of 4 (not impossible given the low flow temps you are already operating at)

 

14.3k gas usage at 5.5p per kwh costs £786pa

14.3kwh gas input at 95% efficacy gas boiler divided by a cop of 4 at 7p per unit off peak rate using battery timeshift costs £238pa

Plus you need to take into account the deletion of the standing charge, if the boiler is deleted which is currently £127 per year.

[Roger440]

4 hours ago, Michael_S said:

Suppose the heat pump gets a cop of 4 (not impossible given the low flow temps you are already operating at)

 

14.3k gas usage at 5.5p per kwh costs £786pa

14.3kwh gas input at 95% efficacy gas boiler divided by a cop of 4 at 7p per unit off peak rate using battery timeshift costs £238pa

 

In theory your heat pump install should be cheap, only need a small unit (6kw?) and only change to plumbing might be to replace the hot water tank with a large coil one and hopefully your battery would be big enough to timeshift your total demand even on the coldest days?  Risk is that the new govt plan to prioritise batteries may lead to a reduction in the potential savings from timeshifting due to increased arbitrage.

 

Where are the battery costs in your numbers?

 

[Michael_S]

3 hours ago, Roger440 said:

 

Where are the battery costs in your numbers?

 

OP said they already had 30kwh battery.  There is a cycle life and therefore a cost per cycle and of course cycle efficiency to update my first order approximation.....

[Johnnyt]

I have been measuring, for a few weeks; outside and internal temps, boiler modulation, cycling, flow and return temps at both the boiler and manifold and finally actual gas usage.

Subsequently fed all this into ChatGPT which gives me a heat loss at 0c actually measured of 4.58kW over several days. I have kept a steady 22c internal temp, .projected heat loss at -5c is 5.7kW.

I therefore think a 7kW ASHP would suit.

The boiler and tank are adjacent to each other, situated in the utility with room for the heat pump control with the fan unit on external wall, the primary circs would be less than 4 feet long.

My emitters need no interference, as they have proved themselves adequate running at a flow temp of 33c, the boiler is cycling about 1 and a half times a day. I have a facility for a 6mm additional radial circuit in the utility. My tank is fine. There is a drain by the external wall for condensate.

In essence if I were to swap it would be a very straightforward exercise.

I know the prices of the heat pumps, I’m going to get three quotes for Viessman, Nibe and SteibelEltron all 7kW and see what they come out with the bus grant.

I may be persuaded dependant on cost but I’ve a feeling they’ll be thousands above the bus grant, in which case, I’m going to sit tight.

The heat loss calc will be interesting to see against my actual heat loss measured from real time data which is marginally better than my SAP calculation from 3 years ago which encompassed an air permeability test.

I uploaded my SAP data to ChatGPT to confirm too, it’s an enlightening tool.

 

Edited Saturday at 06:47 by Johnnyt

[JohnMo]

1 hour ago, Johnnyt said:

7kW ASHP would suit.

Be careful using nameplate rating - you need a heat pump that does just under 6kW at -3 as you are England. Your defrost derate and DHW allowance takes it to just under 6kW.

 

Most important bit is modulation at 7 to 10 degs, that where the heat pump operates most the time - long steady running at there temps makes the difference between SCoP of 4 or 5. 

 

2 hours ago, Johnnyt said:

three quotes for Viessman, Nibe and SteibelEltron all 7kW and see what they come out with the bus grant.

I may be persuaded dependant on cost but I’ve a feeling they’ll be thousands above the bus grant, in which case, I’m going to sit tight.

They will come in thousands above grant, so why are you wasting your time. Your not going to get any change from the grant especially with SteibelEltron, as will cost as much as the grant just buying the unit.

[SimonD]

5 hours ago, Johnnyt said:

I know the prices of the heat pumps, I’m going to get three quotes for Viessman, Nibe and SteibelEltron all 7kW and see what they come out with the bus grant.

I may be persuaded dependant on cost but I’ve a feeling they’ll be thousands above the bus grant, in which case, I’m going to sit tight.

 

I agree with @JohnMo. Yes, these are premium models with great reputations, but there are lots you could choose from that could bring you in under the BUS Grant. If the installation is as straight forward as you describe, I think even a Vaillant unit could give you some change out of the grant too.

[Michael_S]

8 hours ago, Johnnyt said:

I have been measuring, for a few weeks; outside and internal temps, boiler modulation, cycling, flow and return temps at both the boiler and manifold and finally actual gas usage.

Subsequently fed all this into ChatGPT which gives me a heat loss at 0c actually measured of 4.58kW over several days. I have kept a steady 22c internal temp, .projected heat loss at -5c is 5.7kW.

I therefore think a 7kW ASHP would suit.

The boiler and tank are adjacent to each other, situated in the utility with room for the heat pump control with the fan unit on external wall, the primary circs would be less than 4 feet long.

My emitters need no interference, as they have proved themselves adequate running at a flow temp of 33c, the boiler is cycling about 1 and a half times a day. I have a facility for a 6mm additional radial circuit in the utility. My tank is fine. There is a drain by the external wall for condensate.

In essence if I were to swap it would be a very straightforward exercise.

I know the prices of the heat pumps, I’m going to get three quotes for Viessman, Nibe and SteibelEltron all 7kW and see what they come out with the bus grant.

I may be persuaded dependant on cost but I’ve a feeling they’ll be thousands above the bus grant, in which case, I’m going to sit tight.

The heat loss calc will be interesting to see against my actual heat loss measured from real time data which is marginally better than my SAP calculation from 3 years ago which encompassed an air permeability test.

I uploaded my SAP data to ChatGPT to confirm too, it’s an enlightening tool.

 

Your boiler is probably about 95% efficient including the hot water cycle so need to downrate the gas consumption by about 5%|
Do you know if your cylinder has a suitable coil for ASHP?

How far is the installation location from your main consumer unit?

Heat pump warehouse has suitably sized Viessman for about 5.5k inc vat - not sure if it is not the ex vat price that the installer will pay, plus any discount they have negotiated.  https://www.theheatpumpwarehouse.co.uk/product-tag/viessmann/

[sharpener]

9 hours ago, SimonD said:

If the installation is as straight forward as you describe, I think even a Vaillant unit could give you some change out of the grant too.

 

Yes but unfortunately the 7kW Vaillant unit has a poor reputation on account of the defrost performance, the others are much better.

 

ETA @ectoplasmosis might not agree.

 

 

Edited Saturday at 21:22 by sharpener

[SimonD]

1 hour ago, sharpener said:

 

Yes but unfortunately the 7kW Vaillant unit has a poor reputation on account of the defrost performance, the others are much better.

 

ETA @ectoplasmosis might not agree.

 

 

 

True, but you also have to look carefully at the Viessmann outputs as although their performance curves appear to be honest in the reduced output just above 0C, their 8kW is unlikely to perform in this situation so it would probably need to be a 10kW unit going by the rated output as opposed to max output.

 

Someday we might see some consistency around output figures that are also properly localised. Interestingly, I was listening to HVAC education hub's interview with Graham Hendra re his new appointment as an R & D development manager for Haier. He acknowledged that they need different products for different geographical zones due to environmental conditions...so maybe watch this space?

[Johnnyt]

Snap shot of today, internal 21c, external -3.9c, flow, temp at manifold 33c return 28c, delta T at boiler 6.5c accounting for first floor rads.

Boiler modulation 18.1% equivalent to 4525W and gas shows 5200w almost steady, constant burn all night no cycling.

ChatGPT offered the following up.

250104Temperature_Heat_Loss_Report.pdf

[marshian]

4 hours ago, Johnnyt said:

Snap shot of today, internal 21c, external -3.9c, flow, temp at manifold 33c return 28c, delta T at boiler 6.5c accounting for first floor rads.

Boiler modulation 18.1% equivalent to 4525W and gas shows 5200w almost steady, constant burn all night no cycling.

ChatGPT offered the following up.

250104Temperature_Heat_Loss_Report.pdf 2.88 kB · 9 downloads

 

Similar here

OAT overnight -4.4 Deg C

 

All internal room temps held nice and stable overnight

 

Boiler ran from Midnight to just before 10am with one burn (it finished that burn just before the HW cycle was scheduled probably due to OAT warming up or the modulation blips threw the flow temp over target.

 

Avg energy usage for that period 3.81 kWh

 

That's quite impressive considering the modulation hiccups it has on  a regular basis 

 

Looking like my heat loss calcs are a little more than actual ~4.25 kWh @ -2.5 OAT

[Michael_S]

7 hours ago, Johnnyt said:

Snap shot of today, internal 21c, external -3.9c, flow, temp at manifold 33c return 28c, delta T at boiler 6.5c accounting for first floor rads.

Boiler modulation 18.1% equivalent to 4525W and gas shows 5200w almost steady, constant burn all night no cycling.

ChatGPT offered the following up.

250104Temperature_Heat_Loss_Report.pdf 2.88 kB · 16 downloads

Very impressive heat loss.  In theory that outside air temp is actually slightly lower than the heat pump design standard.

 

For heat pump sizing you need to find out if a quoted x kw at -7 (or whatever you decide your actual min point should be) includes defrost cycles.

 

You obviously also need to factor in hot water demand, we do hot water via immersion so know that the 5 of us use more than 25kwh per day so at least 1kw per hour to add on to the space heating demand.

[JohnMo]

6 minutes ago, Michael_S said:

For heat pump sizing you need to find out if a quoted x kw at -7

Not really correct, it's -3 in England and -5 for Scotland a minimum. But another figure you need to comply with designed to satisfy 99.7% of the year. So you ignore the odd day or two of very cold, but if but still needs to comply with -3/-5 and 99.7%. But you also design for a given user comfort. So various room temperature are specified in MCS and these are minimal design standards, a 90 year old or infirmed may want the room temps at 24 etc. There is no given numbers set in stone,it will vary by area. So be careful stating black and white numbers.

[JohnMo]

17 minutes ago, Michael_S said:

 

17 minutes ago, Michael_S said:

25kwh per day

 

On a typical day we add 7 to 10kWh so we add 0.4kW heat pump sizing. This will vary by house size. But can fall back to immersion if we need to.

[Michael_S]

7 hours ago, Michael_S said:

Very impressive heat loss.  In theory that outside air temp is actually slightly lower than the heat pump design standard.

 

For heat pump sizing you need to find out if a quoted x kw at -7 (or whatever you decide your actual min point should be) includes defrost cycles.

 

You obviously also need to factor in hot water demand, we do hot water via immersion so know that the 5 of us use more than 25kwh per day so at least 1kw per hour to add on to the space heating demand.

Sorry for not being clear, the minus 7 was an example arbitrary personal decision on what outdoor temp you want to be able to cover, I can see this was not clear.

Obviously there are the MCS 'rules' based on a set room temp, outdoor temp (by geography) and number of bedrooms which I guess become a minimum if you want the grant but you could obviously decide you want to exceed these to support more hot water or higher room temps or a lower minimum outside temp.