Extra output coil for UVC

[LaChab]

 

The BH heatloss spreadsheet says that I should  need well under 2k for space heating in our new build.

We aren't having UFH, so I'm thinking about using just one or 2 kickspaces (fan coils) in the  lounge / kitchen.

To get over the low water content issue, I was wondering about buying a UVC with an extra output coil at the top to power the space heating.  Effectively a thermal store.
C2Go say no problem specifying one.

Then the heat pump would simply keep the tank at the set temperature, and the space heating cirulation pump would  be controlled by a room stat.

Good idea? Daft? Pointless? All thoughts appreciated.

[JohnMo]

2kW doesn't sound a lot, but that's 48kWh a day at your design day. So would be pulling the cylinder temp down pretty quickly. Then you would be getting a rubbish CoP most the time.

 

Not sure having the heating taken off the top would be that wise, as your DHW would always be cold.

 

Think if you are going thermal store I would go proper thermal store. Have store as a pressure vessel, charge direct from ASHP, so no coils so heat transfer is 100% efficient. So if you store at 50 the heat pump only has to 50 degs flow. Take CH direct from store mid way up and return to bottom. Then have DHW via plate heat exchanger. Size at about 3-400L.

 

[Nickfromwales]

13 minutes ago, LaChab said:

 

The BH heatloss spreadsheet says that I should  need well under 2k for space heating in our new build.

We aren't having UFH, so I'm thinking about using just one or 2 kickspaces (fan coils) in the  lounge / kitchen.

To get over the low water content issue, I was wondering about buying a UVC with an extra output coil at the top to power the space heating.  Effectively a thermal store.
C2Go say no problem specifying one.

Then the heat pump would simply keep the tank at the set temperature, and the space heating cirulation pump would  be controlled by a room stat.

Good idea? Daft? Pointless? All thoughts appreciated.

Bad idea. Keep heating and hot water well apart. 
 

Just use a 50L volumiser and a very small heat pump.

 

Why not go to a split A2A setup and have the bliss of AC to compliment the bit of heating you need? Then just use cheap electric to heat DHW in an oversized UVC. 

[LaChab]

@JohnMo Thanks for all the suggestions. Hadn't thought about affecting the hot water temperature. Suppose I thought the heat pump would just be using the UVC as a large buffer, so it would always be within a few degrees.

That's a very interesting suggestion about a "direct" UVC. I could have a tank with no heat pump coil and two output coils (middle and top) to provide heating and hot water. (prefer a coil to a PHE if there's a choice)

Think I've got room for a 500l cylinder, so would be able to "carry over" quite a bit from the early morning charge up. Ordinary days 1kw should be enough.

[LaChab]

@Nickfromwales I'd really like to take advantage of BUS, and I don't like the idea of using "straight" electricity to heat the hot water.

A small heat pump is exactly what I'd like, but it seems impossible under BUS, so I think I'll be forced into at least 7kw. So using the UVC as a large (giant!) buffer seemed a good idea to reduce cycling.

Agree completely about A2A, and we've had the pipework fitted for a multi split. Just daren't fit it until I get BUS sorted! Then in practice the HP should be almost entirely for producing hot water.

[Nickfromwales]

20 minutes ago, LaChab said:

@Nickfromwales I'd really like to take advantage of BUS, and I don't like the idea of using "straight" electricity to heat the hot water.

A small heat pump is exactly what I'd like, but it seems impossible under BUS, so I think I'll be forced into at least 7kw. So using the UVC as a large (giant!) buffer seemed a good idea to reduce cycling.

Agree completely about A2A, and we've had the pipework fitted for a multi split. Just daren't fit it until I get BUS sorted! Then in practice the HP should be almost entirely for producing hot water.

I'm not so sure your bespoke design would get through MCS, as it's very much away from a "standard installation". For BUS you need an MCS accredited designer and installer, and I think most would cry for their mummy when they are asked to do something that they didn't do yesterday, and the day before, and repeat.

 

I'd buy a cheap as chips ASHP for the outbuilding, and feck the idea of a grant off, and install some fan coils.

 

The go BUS for the house? If I've got this right.

[JohnMo]

3 minutes ago, Nickfromwales said:

buy a cheap as chips ASHP

A HiSense 4.4kW will come down to 1.8kW at 7 degs, so add a 50L volumiser, you will cycle about once per hour. £2100 delivered, plus you can claim the vat back on a new build. So a little over £1800, volumiser £100 to 150. A heat pump cylinder sized at 45L for each bedroom plus 45L, around £1200.

 

MCS as @Nickfromwales says, will want a standard design, so radiators in each room etc. And still charge an arm and leg.

 

If you size you fan coils correctly your flow.temp will never exceed 35 degs for heating, so you should get a scop of 4.5 or better.

[SimonD]

The 4kW Grant unit modulates down to 1.25kW at outdoor temp of 12C and water temp of 30. My own 6.5kW unit has shown itself to tick along quite happily at 1.2kW even though the spec sheet says 2.4kW. As @JohnMo says add a 50l volumiser and this could work.

 

The other option if you decide not to go down the BUS grant route is an exhaust air heat pump like this: https://www.nibe.eu/en-gb/products/heat-pumps/exhaust-air-heat-pumps/s735