Upgrading garage CU

[flashuk]

Hi there

My garage is currently supplied by a 15m 3 core 6mm SWA cable running from an RCD protected CU in the house on a 32A MCB. The garage has an RCD CU with a 16A and a 6A MCB for ring main and light circuit.

Am making some changes to my garage:
- installing underfloor heating (max 2000W)
- might install an air con unit (install manual says it needs a 16A circuit)
- if aircon installed, it will not be used at same time as underfloor heating

Couple of questions:
- given the above additions, and retaining the ring and light circuit, is the existing SWA sufficient?
- if the garage CU is upgraded, would it be sensible to put the underfloor and Aircon each on separate radial circuits, and if so, what size MCB?? 16A for each?
- does the MCB at the house CU need to be bigger?

Many thanks
Flash

 

[DaftPunk]

What are you hoping the underfloor heating will achieve? If you're planning on using it for space heating then forget it. It will be less than useless.

You mention you're thinking of installing air con. Have you thought of having a unit fitted that can do both cooling and heating? Some units can work in reverse. They are known as air source heat pumps and can be up to 400% efficient.

I'd say that your existing supply is certainly borderline, if not undersized for your original plan, but could probably suffice if you forget about the underfloor heating.

What other loads are you planning on using in the garage?

 

[flashuk]

Hi Daftpunk

Am turning the garage into a wine cellar. A ton of insulation also going in to floor, roof and walls. The room needs to at around 10-15 deg C, so realistically it might need air con about 30 days a year, and heating more often.

The air con unit also does heating so that was also an option I was considering. This is the unit:
http://www.tanglewoodwine.co.uk/fondis-c25in-cellar-air-conditioning-unit.html

I thought the under flooring heating would be suitable as the room needs to be kept at a relatively low constant temp.

Best
Flash

 

[ban-all-sheds]

Why not just dig an actual cellar?

 

[flashuk]

Ha ha

I am only just about getting away with this with the wife...even she would notice a cellar being dug out!

 

[winston1]

They are known as air source heat pumps and can be up to 400% efficient.

Rubbish. 400% efficient means it gives out 4 times as much energy as is put into it which is impossible.

Perhaps you mean it is 4 times more efficient than something else but what. Really I don't know what you mean.

 

[stillp]

The problem with using UFH will be that the floor will take much longer to heat up or cool down than your wine, so you could be heating when you don't want to, and then if the outside temperature goes up suddenly you'll overheat the wine with the stored heat in the floor. As you probably know, it is more important to keep a constant temperature (or at least, any changes are very slow) that to have any particular target temperature.
Why not buy a temperature controlled wine cabinet? Otherwise, ditch the idea of UFH build a cabinet for your wine and heat the air in it instead.

 

[flashuk]

@Daftpunk

Thinking about this again, why do you think the 6mm will be borderline? Given it is currently protected by a 32A MCB, and 6mm can handle say 7500W pull easily, surely that is plenty even with 2000W u/f heating? Lights are not going to be more than 400W, and only small stuff on the ring (computer, table lamp, maybe a drill now and then).

Even the aircon only pulls 500W. With everything on full tilt I might get to 4500W. With diversity, going to be less than that, no?

Best
Flash

 

[plugwash]

Rubbish. 400% efficient means it gives out 4 times as much energy as is put into it which is impossible.

A heat pump moves heat from outside to inside. So the heat energy released into the room is greater than the electrical energy put into the heat pump.

 

[RF Lighting]

might install an air con unit (install manual says it needs a 16A circuit)

the aircon only pulls 500W.

Make your mind up

 

[winston1]

Rubbish. 400% efficient means it gives out 4 times as much energy as is put into it which is impossible.

A heat pump moves heat from outside to inside. So the heat energy released into the room is greater than the electrical energy put into the heat pump.

So that is it. Efficiency is not the right word to use however.

 

[flashuk]

@stillp

Not sure this is ever gong to happen though. The u/f heating will only ever kick in below 10 deg C. As soon as the room is 11deg C then u/f switches off...if the outside temp is increasing and then gets to 15deg C in the room, then aircon switches on

Given the level of insulation in the room, massive swings in outside temp are not going to replicate as quickly inside the room. This only really matters during periods of the year when the inside temperature is swinging through the 10 or 15 deg C threshold. In winter this never happens - it is always going to be <10 deg unless the heating is on, and u/f heating is great at sustaining a constant background temp so the room will be at a consistent 10 deg C. In summer ( !?) the room might never fall below 10 deg, so it only needs to deal with the spike in temp above 15 using aircon.

The 5 deg spread in acceptable temp makes it much easier to sustain a temp within the range of 10-15.

F

 

[flashuk]

@RF Lighting

I can only go by what their rubbish spec and installation manual tells me! I agree it appears inconsistent

@daftpunk: maybe it was the 16A for the aircon that had you thinking 6mm was borderline?

 

[ban-all-sheds]

Rubbish. 400% efficient means it gives out 4 times as much energy as is put into it which is impossible.

Well - OK - so it gives out 4 times as much energy as you put into it from the POV of actively putting in energy which you pay for.

Perhaps you mean it is 4 times more efficient than something else but what.

It means that when heating.

Really I don't know what you mean.

That is abundantly clear.

 

[ban-all-sheds]

So that is it. Efficiency is not the right word to use however.

So what would you use to describe a device where you put 1kW in and get 4kW out?