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Author Topic: Cooling with a Robur K18 ASHP  (Read 3313 times)
mesrich
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« on: August 08, 2020, 03:26:11 PM »

Hi All

I'm looking to replace my 30 year old Potterton gas boiler with an ASHP. We have a detatched 4 bed house with standard size radiators throughout. We also have Solar Hot water tubes on the roof with and a Solar Cylinder (vented system). It is quite an old house with good loft insulation and partial cavity wall insulation.

I don't want to change radiators or install underfloor heating so I was thinking of the Robur K18 ASHP which is gas powered as it seems that this will provide hotter water even during cold weather compared with electric ASHP.

I am hoping that the K18 will qualify as part of the Green Home Grant Voucher scheme but this is not yet confirmed and it could be that it is excluded as the government doesn't seem that keen on Gas powered ASHP

So I have 3 questions :
1) Does the K18 sound like a good option for me ?
2) Can the K18 easily replace my gas boiler without impacting my Solar Hot water system/cylinder etc ?
3) On a hot day like today when it is 30 degrees during the day and the bedrooms upstairs are 24 degrees at night time, can I reverse the ASHP and pump cold water around my radiators to reduce the temperature in the bedrooms by a few degrees ?

Many thanks for any advice

Mat

 
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pdf27
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« Reply #1 on: August 08, 2020, 04:48:28 PM »

Cooling with radiators is unlikely to work well - as soon as the water is cold enough to make any noticeable difference, you'll have issues with condensation on the radiators.
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Philip R
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« Reply #2 on: August 09, 2020, 12:23:36 AM »

Been discussed before.
Robur heat pump seems an excellent device and could easily replace a gas boiler and also provide high temperature hot water more easily than an electric vapour compression heat pump.
These devices offer a leap forward from condensing gas boilers, however their price needs to reduce about 65% before they would become an economic proposition.

The Robur K18 is not designed as a reversible heat pump and is not configured as a cooling device.
As PDF27 has said, condensation on radiators is not advisable. Wet carpets and rusting radiator bottoms is not good. Take a look at the radiators fitted in bathrooms and cloakrooms, many with rusty bottoms.
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Barrie
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« Reply #3 on: August 09, 2020, 08:13:43 PM »

I can confirm that. 

After 35 years the "modern" radiator in the bathroom rusted through at the bottom right at the beginning of lockdown.

Fortunately we didn't need it but had to wait until B&Q reopened to get a new one.
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Milton Keynes
pdf27
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« Reply #4 on: August 09, 2020, 09:07:00 PM »

Hmmm... reading the specs it isn't all that impressive on second look.

The Air 7C / Water 50C point (wouldn't really want to go lower for radiators) is 157% efficient. That's 118g of CO2 and ~2.3p per kWh
The equivalent Panasonic heat pump needs a 3 phase supply, but at Air 7C / Water 55C is 271% efficient, probably nearer to 300% at 50C. That's ~60g of CO2 and ~5p/kWh.

With low temperature heating (underfloor) the cost gap closes a bit - 2.25p/kWh for the Robur at 35C and 3.36 p/kWh for the Panasonic.

This assumes 14.4 p/kWh for electricity and 3.8 p/kWh for gas, which flatters the Robur slightly for a well insulated house - it should be possible to shift a fair bit of consumption, so for instance with Agile Octopus most of the day it's at about 6p/kWh at which point the Panasonic is cheaper.
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rogeriko
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« Reply #5 on: August 09, 2020, 09:58:26 PM »

The main problem with using your existing radiators is that they were specd at 80 degree water flow. At 50 degree water flow you only get 53% of the heat output to the room, and at 40 degree water flow which is what you will have reallistically, never believe what the salesman says, you will only have 32% of the heat output from each radiator. We do not install ASHP in old houses, they just dont work.
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brackwell
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« Reply #6 on: August 10, 2020, 06:08:01 AM »

Roger,
Yes all very true, but it can be the case with older houses that the insulation and hence demand can be transformed.   My living room was transformed by insulating the roof, blocking the open fire with a stove and chasing down the draughts. I went from a room that was hardly comfortable on the coldest days to one that can get too hot if i let it.  One of the biggest difference between new and old are the draughty chimneys just sucking the warm air out.


As for cooling.  As i sit here every door and window in my house is open and the house temp is dropping but not very quickly because of high thermal mass, the same thermal mass that kept the house temp a full 10C below the ambient max yesterday.  I will close up everything when the outside temp starts to rise above house and close south facing curtains.   Do you really need ASHP cooling just for a few days a yr.

Ken
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Countrypaul
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« Reply #7 on: August 10, 2020, 08:42:26 AM »

Mat,

One option that has not been disucssed on this thread yet, but might be worth you looking at is an air to air heatpump. This would allow cooling in summer as awell as heating in spring/autumn and warmer winter periods.  It would not provide enough heating when  it is very cold, but certainy in the shoulder months could make a large difference. this could be used along side a replacement boiler (of whatever type)
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brackwell
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« Reply #8 on: August 10, 2020, 09:33:20 AM »

I wonder what is the motivation for changing a working gas boiler?

The problem with ASHP is that they do not evenly distribute heat/cooling around the house so as a background they may be fine but as a workhorse i dont think so.

It could be depending on the size of tubes you have v tank size v demand that the HW performance is not satisfactory.  The most energy efficient/cheapest/easiest solution is to fit a IN line electric heater before the shower. This heater you dial in the temp you require say 42C and the unit will take the water from your HW tank and heat it to 42C by varying the electric this way you are always taking advantage of your solar and you get a good shower.
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todthedog
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« Reply #9 on: August 10, 2020, 10:31:33 AM »

We have an air /air ASHP, just in the lounge/ kitchen can run it off the solar panels cooling on the rare days when needed, use it for heating most of last year we don't like the bedrooms hot. Keeps where we live at a comfortable temp.
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Kidwelly South Wales
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« Reply #10 on: August 10, 2020, 12:10:29 PM »

I wonder what is the motivation for changing a working gas boiler?

The problem with ASHP is that they do not evenly distribute heat/cooling around the house so as a background they may be fine but as a workhorse i dont think so.

It could be depending on the size of tubes you have v tank size v demand that the HW performance is not satisfactory.  The most energy efficient/cheapest/easiest solution is to fit a IN line electric heater before the shower. This heater you dial in the temp you require say 42C and the unit will take the water from your HW tank and heat it to 42C by varying the electric this way you are always taking advantage of your solar and you get a good shower.


The OP said the boiler was 30 years old
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TT
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« Reply #11 on: August 10, 2020, 12:18:16 PM »

I would replace the boiler with a viesmann boiler and leave everything else alone

A heating engineer will do this for you without the scheme increasing the installation costs.
Without hassle of integration of your solar etc,Leave more money for better controls, and other green projects.

As you have a gas supply and arent changing rads this would be choice.
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brackwell
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« Reply #12 on: August 10, 2020, 12:30:16 PM »

I wonder what is the motivation for changing a working gas boiler?

The problem with ASHP is that they do not evenly distribute heat/cooling around the house so as a background they may be fine but as a workhorse i dont think so.

I


The OP said the boiler was 30 years old

Yes i got that but so what?  10-15% less efficient and maintenance free or a more efficient boiler that needs replacing every so often.   Anyway let the OP tell me instead of trying to guess.

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TT
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« Reply #13 on: August 10, 2020, 03:44:33 PM »

No problem, didnt know you only wanted input from the OP
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Philip R
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« Reply #14 on: August 10, 2020, 04:08:09 PM »

30 Year old Potterton eh, would not be one the Netaheat or Profile ranges would it.
A lot of them had positive pressure combustion chamber design which made room sealing a safety issue. Positive pressure boilers were on our radar to do extensive case sealing checks on. A few Worcester 9.24s out their too with similar issues.
Get it replaced with a modern condensing boiler with load and compensating controls and and benefit from improved efficiency and better reliability. Win Win.
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