[David]

I was thinking about air conditioning anyway - longer term fit because I
assume that installers will be very busy at the moment - and assumed that
the standard split unit air conditioning (compressor and heat exchanger
outside, fan unit inside) could also be run in reverse in the winter to
pump heat in the opposite direction.

This is the set up that I have seen abroad, anyway.

Searching UK web sites heat pumps seem to be targeted at grants for
renewable energy and positioned as an alternative heating system.

However one site does say that it can be run in reverse during the summer!

So what is the real difference?
Can only some systems be run in reverse?
I suppose in simplistic terms it is like having a fridge which can also be
an oven, although my cool electric box can also be run as a warm box.

I assume that there is some extra plumbing?
Simplest form is just running chilled coolant from outside through the fan
unit inside.
I can visualise this from simple refrigeration - compress coolant outside
which heats up, lose heat from a heat exchanger outside and then expand
coolant inside to chill, and pass through a low pressure heat exchanger to
cool the surrounding air.

To run in reverse, would you need an extra circuit where the low pressure
half is outside (chill low pressure coolant to below ambient) then have
the high pressure (hot) side indoors?
Or could you just run the compressor in reverse?
I am trying to visualise a suitable device which will act as a pressure
constraint such that one side is high pressure and the other is low
pressure. However a very small hole might be all that is needed.


General idle musing, as air conditioning is what we need and the heat pump
sites (plus Which?) point out that a heat pump may be cheaper to run than
electric, bottled gas or oil heating it is not cheaper than mains gas.


Cheers



Dave R

--
AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[Martin Brown[_3_]]

On 13/08/2020 12:38, David wrote:
I was thinking about air conditioning anyway - longer term fit because I
assume that installers will be very busy at the moment - and assumed that
the standard split unit air conditioning (compressor and heat exchanger
outside, fan unit inside) could also be run in reverse in the winter to
pump heat in the opposite direction.

This is the set up that I have seen abroad, anyway.

Searching UK web sites heat pumps seem to be targeted at grants for
renewable energy and positioned as an alternative heating system.

However one site does say that it can be run in reverse during the summer!

So what is the real difference?

Which heat exchanger has the compressed working fluid inside it and why.

Can only some systems be run in reverse?

Possibly if the low pressure side is incapable of standing the hot fluid
working pressure on the output side of the compressor or it is only
designed to pump the working fluid in one direction. All the ones I have
ever encountered could run either way like a true reversible heat pump.

The only catch I can see with using them for winter heating in the UK as
opposed to a continental climate is that our winters tend to be wet and
humid and the external heat exchange tends to ice up badly as a result.
No air flow through it rather limits how well it can work as a heater.

In Japan they spend most of summer in aircon mode making indoors less
humid and cooler and most of winter in heater mode - though many people
have scary hybrid paraffin heaters as well. They like it warm!

General idle musing, as air conditioning is what we need and the heat pump
sites (plus Which?) point out that a heat pump may be cheaper to run than
electric, bottled gas or oil heating it is not cheaper than mains gas.

Do the sums very very carefully. It has to beat electricity since you
get the gain of the heat pump. It might beat bottled gas. But with
prices are as they stand now it might not beat oil or mains gas.


--
Regards,
Martin Brown

[newshound]

On 13/08/2020 13:24, Martin Brown wrote:


Do the sums very very carefully. It has to beat electricity since you
get the gain of the heat pump. It might beat bottled gas. But with
prices are as they stand now it might not beat oil or mains gas.


If you have a building (or part of a building) that needs aircon as well
as heat you can (perhaps) do it with one system. Perhaps you need a
better design of outdoor unit (vertical plates coated with PTFE, and an
auto defrost system that makes the ice fall off without needing much heat).

I think from time to time about adding a single system to one part of my
house where summer aircon would be nice and I can sometimes use a heat
boost in the winter to supplement the existing traditional gas/water
system. I think there is little doubt that in the long term we will be
going this way (although perhaps more with ground source heat pumps). I
guess one might build a hybrid system with an air HX for heat rejection
in the summer and a ground HX for winter heating.

[Dave Liquorice[_2_]]

On 13 Aug 2020 11:38:08 GMT, David wrote:

Can only some systems be run in reverse?

The heat pump will only work one way.

I assume that there is some extra plumbing?

Simplest form is just running chilled coolant from outside through the
fan unit inside.

Simplest is to have the all the heat pump bits outside,ie compressor,
condensor and evaporator and a couple of dampers that determine which
of the condensor or evaporateor the air flow into the room travels
via. Condensor to heat the air, evaporator to cool it. May even have
options to recirculate or use fresh air.

--
Cheers
Dave.

[George Miles]

With solar panels air source heat pumps should be economic, I hope
[george]

On Thursday, August 13, 2020 at 1:24:07 PM UTC+1, Martin Brown wrote:
On 13/08/2020 12:38, David wrote:
I was thinking about air conditioning anyway - longer term fit because I
assume that installers will be very busy at the moment - and assumed that
the standard split unit air conditioning (compressor and heat exchanger
outside, fan unit inside) could also be run in reverse in the winter to
pump heat in the opposite direction.

This is the set up that I have seen abroad, anyway.

Searching UK web sites heat pumps seem to be targeted at grants for
renewable energy and positioned as an alternative heating system.

However one site does say that it can be run in reverse during the summer!

So what is the real difference?
Which heat exchanger has the compressed working fluid inside it and why.
Can only some systems be run in reverse?
Possibly if the low pressure side is incapable of standing the hot fluid
working pressure on the output side of the compressor or it is only
designed to pump the working fluid in one direction. All the ones I have
ever encountered could run either way like a true reversible heat pump.

The only catch I can see with using them for winter heating in the UK as
opposed to a continental climate is that our winters tend to be wet and
humid and the external heat exchange tends to ice up badly as a result.
No air flow through it rather limits how well it can work as a heater.

In Japan they spend most of summer in aircon mode making indoors less
humid and cooler and most of winter in heater mode - though many people
have scary hybrid paraffin heaters as well. They like it warm!
General idle musing, as air conditioning is what we need and the heat pump
sites (plus Which?) point out that a heat pump may be cheaper to run than
electric, bottled gas or oil heating it is not cheaper than mains gas.
Do the sums very very carefully. It has to beat electricity since you
get the gain of the heat pump. It might beat bottled gas. But with
prices are as they stand now it might not beat oil or mains gas.


--
Regards,
Martin Brown

[newshound]

On 13/08/2020 14:47, George Miles wrote:
With solar panels air source heat pumps should be economic, I hope
[george]


How would you cope with the problem of ice formation in typical western
european winters?

[George Miles]

"a defrost cycle does runs the heat pump backwards. Rather than using ambient air as the source of heat, a small amount of hot water from inside your home is used to melt the ice on the coils"
https://www.evergreenenergy.co.uk/he...ump-in-winter/

On Thursday, August 13, 2020 at 3:02:51 PM UTC+1, newshound wrote:
On 13/08/2020 14:47, George Miles wrote:
With solar panels air source heat pumps should be economic, I hope
[george]

How would you cope with the problem of ice formation in typical western
european winters?

[Theo[_3_]]

David wrote:
So what is the real difference?
Can only some systems be run in reverse?
I suppose in simplistic terms it is like having a fridge which can also be
an oven, although my cool electric box can also be run as a warm box.

ASHPs in the UK are often targeted at wet heating systems (ie radiators).
It's not a good idea to run one of those in reverse because you'll get a
puddle of condensation under the radiator.

Air conditioning systems can often heat too, and I think that is heat pump
mode rather than a big resistor, but those are hot air systems.
You'd either need a big ventilation duct system, or need to have a unit in
every room to dispense air.

I don't know if there's something you can plumb an ASHP into that's like a
radiator but for cooling, which handles the condensation?

Theo

[Andy Burns[_13_]]

Martin Brown wrote:

The only catch I can see with using them for winter heating in the UK as
opposed to a continental climate is that our winters tend to be wet and
humid and the external heat exchange tends to ice up badly as a result.
No air flow through it rather limits how well it can work as a heater.

If the O/P is looking to install an ASHP with under the RHI scheme

1) get your skates on as it closes (AFAIK) at the end of March

2) I think heat-only pumps are eligible, and reversible heating/cooling
pumps are ineligible ... thought there might be a "wheeze" where it can
be installed as the former, then retrofitted to the latter?

[Paul[_46_]]

Dave Liquorice wrote:
On 13 Aug 2020 11:38:08 GMT, David wrote:

Can only some systems be run in reverse?

The heat pump will only work one way.

I assume that there is some extra plumbing?

Simplest form is just running chilled coolant from outside through the
fan unit inside.

Simplest is to have the all the heat pump bits outside,ie compressor,
condensor and evaporator and a couple of dampers that determine which
of the condensor or evaporateor the air flow into the room travels
via. Condensor to heat the air, evaporator to cool it. May even have
options to recirculate or use fresh air.


Heatpump with reversing valve in its two positions.
Heating in winter, cooling in summer.

http://www.elephantearshvac.com/?p=288

At -20C external air temp, with an air-source heatpump,
you switch off the heatpump and go to your aux heating
system. You don't allow the heatpump to use the
clever electric element it uses to augment output
at the extremes. I think people leave the heatpump
off, even when the outside air temp returns above
-20C and just use their other system instead. Until summer.
I don't see evidence of people flipping around their
system, all winter long. Even if it was -4C in March,
nobody would bother to go back to the heatpump.
They probably like the feel of the higher
quality heat anyway. It's probably heat quality,
that drives them away from that heatpump in winter.

*******

There are some heatpumps in my neighborhood. There's
a lower limit in winter, when it's no longer possible
to extract heat from the out-of-doors air, to heat
the house interior. That's when a person might
install a ground-source heatpump, where the source
of heat is less variable compared to outdoor air.
I'm not aware of any ground-source installs in
my neighborhood, but it's pretty hard to see because of hedges.

Some ground-source heatpumps are connected to adjacent
waterways - to do that here requires permits, and isn't
a sure thing. They don't like it if you drop a couple 2 inch
lines into a stream, and dump your heat (or cold) into
that water.

And heat has "quality". People using oil-fired furnaces
with air circulation (air handler), if you come in
from the outdoors in winter and put your feet next to
the airflow, the air is pleasantly warm. Lots of delta_T
to warm "frost-bitten" feet.

Whereas a heatpump, the air is barely above ambient,
makes a lousy footwarmer, and will take substantial hours
of operation to heat the house. But you're "winning",
since from an energy perspective, most of the heat
or cooling is being extracted from somewhere. It would
not use nearly as much electricity as pure electric heat.

The same goes for air-conditioning. It works best
if left thermostatically controlled. If you have
time-of-day electricity billing, you can run your
air conditioning in "batch mode", but this is what
happens if you do.

7PM 86F lying naked on the bed, sweating
3AM 70F pulling covers over, because you're cold.
system now switched off - you don't pump
below 70F because it might "freeze the coil".

Noon ?? Still comfortable because of the 40% RH
inside the house. Will be miserable at 5PM.
Cursing and waiting for switch-on at 7PM.

About two degrees F per hour, is a good rate to
properly dehumidify the air. The next day, with the
dried air, you're comfortable until noon, then start
to suffer from noon until 7PM (if that's when the
cheap electricity arrives).

*******

The older systems with R12, were good because the gas
didn't tend to leak out of them. My old system had been
run by the previous owner for some number of years,
and when I got the house, I didn't add any gas over
a period of 20 years operation.

The newer systems that don't use R12, are more
prone to leakage. Pinhole leaks in the A-coil
are common. You might need a recharge after four
years. The very latest gas-substitute was obviously
selected to bankrupt people.

If you had half a dozen split-units running crappy
materials like that inside, you would be in for
a world of hurt, in terms of maintenance calls.

Even new portable units on wheels, you can leave
one of those in storage until the next hot spell,
switch it on and... no gas. Why, it's enough
to make you want to place *combustible* organic gasses
in there :-/ Lower pressure, less leak prone. Whether
they're doing that, you'll want to check the specs
carefully to see if they've moved to the Dark Side.
They've put combustible gases in fridges - there is
a precedent.

On the R12 system, electric bill was $200 per month during
summer. On the spiffy-gas system, with an external
unit with a much higher SEER rating, electricity is
$100 per month (using the 7PM electricity). However,
when the system needs a recharge, you could easily
burn up all the savings in recharge gas, new A-coil,
and so on.

Paul

[The Natural Philosopher[_2_]]

On 13/08/2020 14:47, George Miles wrote:
With solar panels air source heat pumps should be economic, I hope
[george]
winter night output of solar panels = 0kW
winter night heating demand = 10kW

Go figure


--
Climate Change: Socialism wearing a lab coat.

[Roger Hayter[_2_]]

Theo wrote:

David wrote:
So what is the real difference?
Can only some systems be run in reverse?
I suppose in simplistic terms it is like having a fridge which can also be
an oven, although my cool electric box can also be run as a warm box.

ASHPs in the UK are often targeted at wet heating systems (ie radiators).
It's not a good idea to run one of those in reverse because you'll get a
puddle of condensation under the radiator.

Air conditioning systems can often heat too, and I think that is heat pump
mode rather than a big resistor, but those are hot air systems.
You'd either need a big ventilation duct system, or need to have a unit in
every room to dispense air.

I don't know if there's something you can plumb an ASHP into that's like a
radiator but for cooling, which handles the condensation?

Theo

They need a drip tray and, probably, a condensate pump. And therefore
probably an outside casing to hide all that. You can get fan assisted
ones like that.
--

Roger Hayter

[Andy Burns[_13_]]

Andy Burns wrote:

the RHI scheme [...] closes (AFAIK) at the end of March

It's been extended until March 2022, then it gets replaced with a
smaller grant (£4k I think)

[Cynic[_2_]]

I've got a Mitsubishi split system on the landing. So far I've only used it to cool the house which it does quite usefully with the exception of one bedroom because of house geography. Yesterday this was remedied by adding a second unit in the problem bedroom, Fujitsu this time.
Both models can run as heating if required by simple selection on the handheld remotes. A couple of changeover valves in the units take care of the reversal of duties.
Out of interest yesterday's instal started at 10 am and was commissioned around 4 PM. At that time bedroom temperature was 27 degrees. By 4.30 with the unit set point 21 degrees the room temperature was down to 21.5 degrees. Condensate trickling out of the drain line outdoors. Indoor humidity reduction is a useful side effect and you get distilled water if you need it.
For winter heating I had a Vaillant air to water unit installed plus radiators upgraded. This was funded by a bank loan which the RHI payments will cover. I did ask if air to air RHI was available but apparently not at that time.