Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.

Question.

Will a modern 100amp consumer unit be able to handle this?

Will it be simply a case of having two 32amp mcb in the consumer unit
and feed each air pump with a cable from
each? For the coldest periods I would expect both units to be
operating most of the time therefore drawing 36amps.

How much current can you draw from a domestic supply cable? If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.

Advice please.

wrote:
Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.

Question.

Will a modern 100amp consumer unit be able to handle this?

Yes, it's only the same as a smallish electric shower.


Will it be simply a case of having two 32amp mcb in the consumer unit
and feed each air pump with a cable from
each?

You could do it that way, yes.

For the coldest periods I would expect both units to be
operating most of the time therefore drawing 36amps.


You need to assess existing maximum demand and diversity and see if
there is scope for adding this extra load.

How much current can you draw from a domestic supply cable?

This is the $64,000 question.

You consumer unit may well be rated at 100A. You may well have an
electricity board cut-out with a fuse holder that's rated at 100A.

However, the fuse in the cut-out may be 40A, 60A, 80A or 100A. You will
only know this by removing the fuse and having a look, which most likely
will involve cutting off the electricity board seal.

Also, the rating of the fuse may not reflect the capacity of the supply
cable (i.e. it may be a 60A fuse on a supply that's good for 80A or it
may be an 80A fuse on a supply that's barely adequate for 80A, or 80A
fuse on a supply that's good for 100A, etc). You can only tell by having
someone experienced to assess the size of your supply cable and
measuring the source impedance of your supply. This will inform whether
the existing fuse (a) is correct and (b) can be safely upgraded to the
next size.

In my limited experience, most houses have a 60A or 80A fuse.

If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.


Unlikely to overload the consumer unit, but yes in principle you could
have two consumer units on the same supply cable.

On Thu, 24 Dec 2009 17:12:32 +0000, Dave Osborne wrote:

wrote:
Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.

Question.

Will a modern 100amp consumer unit be able to handle this?

Yes, it's only the same as a smallish electric shower.

but don't be surprised if you notice the lights dim/flicker a little on starting, especially if
you're towards the end of the line

In an earlier contribution to this discussion,
wrote:

Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.

Question.

Will a modern 100amp consumer unit be able to handle this?

Will it be simply a case of having two 32amp mcb in the consumer unit
and feed each air pump with a cable from
each? For the coldest periods I would expect both units to be
operating most of the time therefore drawing 36amps.

How much current can you draw from a domestic supply cable? If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.

Advice please.

What's the rating of your main fuse and electricity meter - because they
might determine the max current you can draw.

What size property are you heating - something akin to Buck House? 36 amps
is about 9kW *just* to drive the pumps! You can heat a fair-sized property
with 9kW of heat - and gas is a lot cheaper than on-peak electricity!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Dec 24, 6:05*pm, "Roger Mills" wrote:
In an earlier contribution to this discussion,





*wrote:
Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

The trianco activair units quote a start up current of 23amps which
then drops to 17.7amps for normal operation.

Question.

Will a modern 100amp consumer unit be able to handle this?

Will it be simply a case of having two 32amp mcb in the consumer unit
and feed each air pump with a cable from
each? For the coldest periods I would expect both units to be
operating most of the time therefore drawing 36amps.

How much current can you draw from a domestic supply cable? If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.

Advice please.

What's the rating of your main fuse and electricity meter - because they
might determine the max current you can draw.

What size property are you heating - something akin to Buck House? 36 amps
is about 9kW *just* to drive the pumps! You can heat a fair-sized property
with 9kW of heat - and gas is a lot cheaper than on-peak electricity!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!- Hide quoted text -

- Show quoted text -

I am heating with oil so air source is a good lot cheaper than oil
1kw in = 3-4kw out. Plus very little servicing and no oil tank
required.
An average size house requires 12kw of heat just
to maintain temperature in cold spells.

In an earlier contribution to this discussion,
wrote:


I am heating with oil so air source is a good lot cheaper than oil
1kw in = 3-4kw out. Plus very little servicing and no oil tank
required.
An average size house requires 12kw of heat just
to maintain temperature in cold spells.


So why do you need 9kW to drive the pumps - 3 or 4 should be more than
enough?!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Thu, 24 Dec 2009 22:25:49 -0000, Roger Mills wrote:

I am heating with oil so air source is a good lot cheaper than oil
1kw in = 3-4kw out. Plus very little servicing and no oil tank
required. An average size house requires 12kw of heat just
to maintain temperature in cold spells.

So why do you need 9kW to drive the pumps - 3 or 4 should be more than
enough?!

I suspect he's still think in normal boiler all or nothing mode and
needs 25kW to heat water directly like a combi (spit).

Heat pumps doen't work like that you can't just switch it on and have
an instant 25kW of energy available like a gas or oil boilier. What
needs to be done is calculate the average daily energy demand during
the winter and have a heat bank/thermal store that you replenish
(heat wise) from the heat pump. The heat pump still needs to provide
a goodly proportion of the requirement but not all of it. The heating
will be off or set back at night and possibly during the day so the
average energy demand is lower than the peak. Size for the average
not the peaks.

--
Cheers
Dave.

On Dec 24, 9:15*pm, "
wrote:
I am heating with oil so air source is a good lot cheaper than oil
1kw in = 3-4kw out.

Assume 2.5kW out for 1kW in (CoP = 2.5).
Perhaps Economy 7 backup for when CoP tends to 1.

Plus very little servicing and no oil tank required.
An average size house requires 12kw of heat just
to maintain temperature in cold spells.- Hide quoted text -

12kW heat at CoP 2.5 means ASHP of 4.8kW :-)



I thought domestic ASHP were 9kW and 14kW.

Basically...
- Single 9kW unit would be ok (or 12kW in this instance)
- Thermal Store suitably sized (acts like a buffer / battery)
- Backup by a) E7 Storage Heaters, Automatic (plain reliability)
- OR b) 5-9kW run electric inline boiler
- OR c) 2x 3kW thermal store elements

The backup are for if it is serviced, any failure, so cold that ASHP
ends up dropping to CoP 1 (ie, parity 12kW in = 12kW out as opposed to
12kW in and 24kW out).

No idea what prices you have been quoted, but also look at the Sanyo
CO2 heat pumps - they are very powerful and CO2 based so they really
DO produce very high CoP at very low temperature (night time operation
in deep UK winter is no problem, they are rated to CoP 1.0 down to
-25oC and optimised for cold weather).


Also consider insulation.
If you are solid wall, at least consider Celotexing the main living
area - disruptive but the difference between say solid-wall and
65-90mm of Celotex/Kingspan is enormous. A hamster running around will
make you reach for a cooling fan.

On Dec 24, 4:28*pm, "
wrote:
I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.

Is one for backup, or both simultaneously?

Both ASHP simultaneously...
- 48kW heat output @ CoP of 2.0
- 60kW heat output @ CoP of 2.5
- 72kW heat output @ CoP of 3.0

If you want 48-60kW to replicate a "massive kW combi"...
- Consider using a thermal store instead
- Then booster element if necessary for 45oC to 60oC

If you are using two ASHP serially to boost temps?
- Consider fitting underfloor heating
- Alternatively oversizing radiators to assist

I assume you do not have a pile of land you can stick GSHP pipes under
- there is no PP required for that as it comes under Permitted
Development whereas ASHP doesn't due to still undecided noise
standards at present.


The trianco activair units quote a start up current of 23amps
which then drops to 17.7amps for normal operation.

Invertor units probably, so gently on the startup - it may say it
needs Type-B circuit breaker rather than Type-C or even Type-D that
some HVAC systems require (which is fun to get EFLI low enough re
supply & final circuit, although RCDs are your friend here and 17th
likes them too).


Will a modern 100amp consumer unit be able to handle this?

Yes, indeed it is not an issue.
- If the units are invertor based their current draw is a) soft start
b) varies based on load. Invertor based units use DC compressor whose
speed varies rather than cycling on/off - better efficiency at a
higher price.
- Eventually CO2 air pumps will be cheaper which will boost your CoP
hugely even at very low temperatures (uses 2 stage DC compressor).

The problem might be your supply.
- If the units are invertor, the load is soft start & varies - so you
don't get "light dimming" which would be otherwise pretty severe.
- Your supply might be 60A by design, does not give you much headroom
re load.


How much current can you draw from a domestic supply cable? If one
consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.

They generally say 9kW electric boiler, or slightly more for a shower
(because a shower is not running continually). With appliances like a
cooker you have diversity, with a 9kW electric boiler there is no
diversity but the supply company assumes a certain diversity when
sizing supply cables, pole transformers and so on.

If the ASHP are invertor based their demand actually varies from
probably 4-12kW, rather than 12kW on/off.

So it depends on what your supply is.

wrote:
Hi group,

I am considering installing two 12kw air source heat pumps to replace
my old oil fired boiler.


Isn't an "air source heat pump" just another word for "air conditioner with
reverse cycle mode".

How come "air source heat pump = green" but "air conditioner = not green"?