What plumbing/cabling/preparation is needed to prepare for ASHP in the future?

bobfredbob

Thanks, that was very useful to see the pictures of what the tank actually looks like when fitted.

Since I'll have a kitchen flue hole too, may I ask why you installed an MVHR in the kitchen?

DougMLancs

bobfredbob said:

Thanks, that was very useful to see the pictures of what the tank actually looks like when fitted.

Since I'll have a kitchen flue hole too, may I ask why you installed an MVHR in the kitchen?

There was no extractor in the kitchen (over the hob or in the wall) when we bought the house so this way we can maintain ventilation without drawing in cold air. 

NedS

Some considerations:

1. Try to locate the heat pump as close as possible to the hot water cylinder - the shorter the pipe runs, the better.

2. The pipe run from ASHP to cylinder should be very well insulated 28mm copper. The primary central heating should 22mm to radiators, teeing off at 15mm to connect.

3. You will either need anti-freeze (glycol) or anti-freeze valves. If you go for glycol, you will need to replenish each time you drain down the system (and it's not cheap).

4. You'll need two breakers - one for the ASHP and another for the 3kW cylinder immersion.

5. Work out the heat loss for your property. Size your radiators for 40C flow temps at your coldest outdoors temps depending where you live (-2C here). Ensure your chosen heat pump can output the required heat at those temps.

6. You may need a volumiser to ensure the system has sufficient volume of water to work with. A volumiser is more efficient than a buffer tank or low loss header. A volumiser should be fitted to the return flow. You may not need a volumiser if you have sufficient volume in your pipework/radiators, but the volume is useful for defrost cycles.

FreeBear

NedS said: 2. The pipe run from ASHP to cylinder should be very well insulated 28mm copper. The primary central heating should 22mm to radiators, teeing off at 15mm to connect.

5. Work out the heat loss for your property. Size your radiators for 40C flow temps at your coldest outdoors temps depending where you live

Depending on the number of radiators (or to be more precise, the heat load), and the length of the pipes, you may want 28mm for part of the feed/return.

It is also worth running the heat loss calculations based on a flow temperature of 35°C - The lower the flow temperature, the higher your potential efficiency is. But lower flow temperatures could mean excessively large radiators, so there may well have to be compromises.

Reed_Richards

Or you may find that using a flow temperature of 35°C or 40°C requires you to use radiators that are too large to fit in the space you have available and you are forced to use a higher temperature.  But the aim is to make the (maximum) flow temperature as low as you can in order to achieve the best efficiency and therefore the lowest running cost.  

stripling

saveallmymoney said:

bobfredbob said:

Thanks for the info on the amps.  I've no idea the actual kw I would need, but you're right, even at 5kw it would require 5000w/240v=21amps, so I imagine a minimum 32amp dedicated wire would be put in.

I'll have to check the fusebox rating since we have a 9.5kw electric shower and I remember we couldn't (easily) have two electric showers fitted to be on at the same time.

So would this mean losing the electric shower if we have a heat pump?  The unvented will give a better shower than electric, and I guess the immersion is good enough as a backup.

Out of curiosity, how do people with concrete floors/mid-terrace do these type of new cable runs?

5KW is the output, not the input. My 7kw Daikin says it should be on a 19+ amp circuit, but the max draw is only about 9 amps.

However if your unit has a backup electric heater, that can increase the required circuit size considerably.

Hi @saveallmymoney what do you think of your 7kw Daiken ? Are you happy with it? 

stripling

@NedS

1. Try to locate the heat pump as close as possible to the hot water cylinder - the shorter the pipe runs, the better.

Does this matter very much if the pipe run is in a cellar that has cavity wall insulation? The cylinder would be in a connected garage and the pipes would run about 18-20 meters under the ground floor which would be at ceiling height in the (stand up) cellar and through the cellar wall? 

stripling

@bobfredbob

I'd not heard of R290, which can apparently heat to 75C.  I imagine the promotion heat pumps (Octopus, etc.) are an older variety, but I would have to look in to it.  Though one manufacturer warned that the problem with R290 is that people then won't insulate their properties and so incur higher costs.

You might find this video interesting -       it's Dr Jason Cassells the man who designed Octopus' new not-yet-released Cosy Heat Pump 

Reed_Richards

stripling said:

@NedS

1. Try to locate the heat pump as close as possible to the hot water cylinder - the shorter the pipe runs, the better.

Does this matter very much if the pipe run is in a cellar that has cavity wall insulation? The cylinder would be in a connected garage and the pipes would run about 18-20 meters under the ground floor which would be at ceiling height in the (stand up) cellar and through the cellar wall? 

You are bound to lose some heats from the pipes, and the longer they are the more heat you will lose.  You can try to minimise this by making sure the pipes are very well insulated.  And if the pipes are within the heated fabric of the building then that heat is not wasted at those times of year when you are running your central heating.

You will also lose heat from the cylinder, so much better if this is inside the heated fabric of the building than in  a garage.  

NedS

Reed_Richards said:

Or you may find that using a flow temperature of 35°C or 40°C requires you to use radiators that are too large to fit in the space you have available and you are forced to use a higher temperature.  But the aim is to make the (maximum) flow temperature as low as you can in order to achieve the best efficiency and therefore the lowest running cost.  

Indeed. You can always work backwards, starting with the largest radiators you can reasonably accommodate and then calculate the flow temp that would give the required heat output to match your heat losses. You will then have a good idea what flow temps you will be able to run at, and consequently how efficient the system is likely going to be.

We replaced all our radiators as part of our install, going as large as reasonably possible in each room, and adding additional radiators in larger living spaces where possible. Use K2 throughout - you can use little tricks like going from 600mm to 700mm height where possible which adds useful output, and we managed to squeeze some 600mm radiators under low windows where 450mm had previously been fitted. You always have the option of K3's in any room where you are really struggling to accommodate large enough radiators, but we managed to find a good balance with K2's throughout. Then there are vertical radiators if you are struggling for horizontal wall space.