ASHP – Should do better - Must Do Better

lovesgshp

Quote:
Originally Posted by TiredGeek
Here's a little question about MCS accreditation aimed at those in the know:
If a company just supplies the EcoDans and a set of instructions, leaving the client to carry out the instalation, then simply does a commissioning, does this comply with MCS?

I'm thinking not, but I'd like other opinions on this.....

I am cautiously edging towards a Heat Pump installation, especially if and when we get the final details of the RHI.

I have a friend in the fortunate position of owning a summer time retreat in the form of an 19th century farm house. He needs to keep the frost out of it, when it is left more or less unattended for 4 months of the year. (it is a "holiday let" in the summer).
He has been targeted by heat pump salesmen.
I think I've persuaded him that better controls on the oil boiler are a more sensible choice, at least for the next few years.

These are my understandings of Heat Pump technology:
Note the point about the MCS process will require a proper SAP study in the not too distant future and this is likely to be combined with proper training for the new user of this "new to us" technology.

http://www.bre.co.uk/sap2009/page.jsp?id=1642


DOMESTIC INSTALLATIONS
Not a simple replacement for 80 degree boiler.
90k btu = 23kWp
Typical HP is 10 kW.

A Calculate the heat losses SAP for internal and external temperatures (-2?)
Approved software will soon be a requirement for MCS certification.
Software has always been available, a requirement here for sizing. ( Quite expensive so can see why not used so much in the UK ).
B Improve the house so 10kW will service it. (£300 on insulation = £3000 saved on HP.)
Good point, but not always possible
C Heat Pump selection. Aim for 100% heat pump at design temperature not 70%
You can go to 10% below
D Choose back up heating. Log burner?
For power cuts a good idea
E DWH ? ? E7 night electric?
DHW is usually only 20% of pump output.
F Under floor heat at 35 not radiators at 45.
The right spec ASHP's heatpumps can deliver 50c for rads, plus you can also boost with special tanks.
G Beware of cycling.
H Beware of Zoning.
I 10 mins a week for legionaire.
OK, if DHW temp is low, otherwise heat delta should eliminate.
J 55 degree DHW requires a big tank.
Why?
K Inverter control? 12 – 14 kW is the max for single phase.
A soft start is normally required for single phase. 3 Phase is a little more economical in terms of electricity usage
L Buffer tanks prevent cycling.
Only realy needed for radiator systems, UHF combined with rads, multiple floor temperature zones.
M Modern GSHP noise in not an issue. ASHP it still can be
N Thermal mass allows thermostat differentials to be 7 – 8 degrees not 1 – 2
Heat delta ranges can be changed in the pumps on setup, so if you want 1-2 degrees before the pump switches in it's easy

lovesgshp

Cardew wrote: »

Do you fit ASHPs as well as GSHPs?

GSHP, ASHP only as specialise in this field.

harryhound

Many thanks for the replies; I think we largely agree; though your further thoughts would be useful on the following.

Geotherm wrote: »

E DWH ? ? E7 night electric?
DHW is usually only 20% of pump output.
Does it make economic and engineering sense to run the pump in the summer to achieve high temperature output for a small load, given all the losses involved in cycling the system - not efficient and wears out the pump? Feels a bit like racing down to the newsagent half a mile away in a 4 x 4, when there is push bike in the garage.
What sort of COP would be achieved on hot water only?
Just give it some E7 electricity?
F Under floor heat at 35 not radiators at 45.
The right spec ASHP's heatpumps can deliver 50c for rads, plus you can also boost with special tanks.
But with a poor COP/[FONT=&quot]SPF (Seasonal performance factor) and a pump that will turn on a big immersion heater when it can't cope in the depths of winter? [/FONT]
J 55 degree DHW requires a big tank.
Why?
Presumably because there won't be much need for adding cold to a bath or shower and perhaps because the re-heating of an cold tank will take longer with a heat pump?,
Heat delta ranges can be changed in the pumps on setup, so if you want 1-2 degrees before the pump switches in it's easy
But the wider thermostat range is needed to minimise the cycling of the system (turning on and off). Here in the UK the energy supplier can specify a maximum cycling rate (eg once an hour) because they don't want complaints about voltage drops (flickering lights in neighbouring houses) as the pump motor kicks in? Cycling can cause premature failure of the pump?.

Cardew

Does it make economic and engineering sense to run the pump in the summer to achieve high temperature output for a small load, given all the losses involved in cycling the system - not efficient and wears out the pump? Feels a bit like racing down to the newsagent half a mile away in a 4 x 4, when there is push bike in the garage.
What sort of COP would be achieved on hot water only?
Just give it some E7 electricity?

Then you have the dilemma of paying a premium(often 20%ish) on the other 17 hours of electricity, and with an ASHP you will use a lot of daytime electricity.

I would have thought it cheaper to use the ASHP for a couple of hours(or as long as it takes) just to heat the hot water tank. Even with a COP of 2.0 which should be achieved with the high ambient temperatures in spring/summer, it will be as cheap as E7.

lovesgshp

Does it make economic and engineering sense to run the pump in the summer to achieve high temperature output for a small load, given all the losses involved in cycling the system - not efficient and wears out the pump? Feels a bit like racing down to the newsagent half a mile away in a 4 x 4, when there is push bike in the garage.
What sort of COP would be achieved on hot water only?
Just give it some E7 electricity?

Pumps are designed for long life and regular use, just like a fridge. We have a 160ltr DHW and normal running to keep water hot averages 1 hour per day. COP figures to say 50C should be specified in the technical data.

But with a poor COP/[FONT=&quot]SPF (Seasonal performance factor) and a pump that will turn on a big immersion heater when it can't cope in the depths of winter?

Ours has only used electric backup for 24 hrs over a 5 year period, and the bulk of that for disinfection. We have it set on 3Kw.

[/FONT]Presumably because there won't be much need for adding cold to a bath or shower and perhaps because the re-heating of an cold tank will take longer with a heat pump?,

Normally after running a bath, recharge to temp here is circa 15min, cycling on temp delta of 5C on normal use approx 5 mins.

But the wider thermostat range is needed to minimise the cycling of the system (turning on and off). Here in the UK the energy supplier can specify a maximum cycling rate (eg once an hour) because they don't want complaints about voltage drops (flickering lights in neighbouring houses) as the pump motor kicks in? Cycling can cause premature failure of the pump?.

I agree, just saying it can be changed on installation. Soft start on single phase pumps reduces the kick-in fluctuation. I don't know about all manufacturers, but the pumps we use have 10 year compressor guarantees.

harryhound

Whose pumps do you use?

lovesgshp

All ours are IVT Swedish units

harryhound

Bosch certainly liked them!!

Over here in UK they were pushed by Ice Energy (in the ground source format) which created the rather bizarre situation of Ice Energy (who at least had some experience even if they did over sell) facing Worcester-Bosch across a gangway with both of them trying to sell the same kit.
Worcester-Bosch had a nice film of their managing director having a new pre-made grid of heat gathering plastic pipes being dug into his lawn.
I think the gas fitters on their stand were somewhat bemused.

Presumably the situation has now settled down with Ice Energy handling the wealthier clients?

I wonder who designed this:

GSHP: UK, 1998 [25] An IVT Greenline 4 was installed with two 2kW immersion heaters in a large detached home in the UK, and monitored for around one year. Outlet temperatures were 45°C for under-floor space heating, and 50°C for hot water. The COP of this system was limited by the choices made during installation. COP of the heat pump was 3.16 during this time, but was reduced significantly due to a circulation pump set to run continuously. If this pump ran only when the heat pump was operating, the COP was estimated to be 3.43. The heat pump was sized to only provide 50% of the annual heating demand, so usage of the low- efficiency immersion heaters was significant. These consumed 2.8MWh of electricity, compared to 5.0MWh from the heat pump itself – reducing the overall system’s performance factor to 2.39. This would have increased to 2.52 if the circulation pump was optimised. The monthly COP was not seen to vary between summer and winter, as summer demand was mostly for higher temperature hot water.

Cardew

harryhound wrote: »

GSHP: UK, 1998 [25] An IVT Greenline 4 was installed with two 2kW immersion heaters in a large detached home in the UK, and monitored for around one year. Outlet temperatures were 45°C for under-floor space heating, and 50°C for hot water. The COP of this system was limited by the choices made during installation. COP of the heat pump was 3.16 during this time, but was reduced significantly due to a circulation pump set to run continuously. If this pump ran only when the heat pump was operating, the COP was estimated to be 3.43. The heat pump was sized to only provide 50% of the annual heating demand, so usage of the low- efficiency immersion heaters was significant. These consumed 2.8MWh of electricity, compared to 5.0MWh from the heat pump itself – reducing the overall system’s performance factor to 2.39. This would have increased to 2.52 if the circulation pump was optimised. The monthly COP was not seen to vary between summer and winter, as summer demand was mostly for higher temperature hot water.

Am I having a blond moment or are the calculations here a nonsense?

The output of the heat pump was 5MWh with a COP of 3.16.

This means it used 1.582MWh to produce the 5MWh.(5 divided by 3.16)

It used a further 2.8MWh in the immersion heaters(obviously at a COP of 1)

So to produce 7.8MWh(5 + 2.8) it required 4.382MWh(2.8 + 1.582)

That to me indicates the overall COP is 1.78 (7.8 divided by 4.382) and not 2.39 as stated in the quote above.

Comments?

Edale

I think the heat pump consumed 5mwh of electricity giving a heat output of 3.16 times this or 15.8mwh, add the immersion heaters and you have an annual heat requirement of 18.6mwh. This sounds more realistic for a large detached home than 7.8mwh it would be using your calculation.