fan boosted radiator - how well does it work? Useful for heat pump?

[Theo]

If you go for split units, you can have 3 or 4 room units per outdoor unit, but not much more than that. All those room units share the capacity of the outdoor unit. That's probably fine for a flat, but if you have a house you end up with needing several outdoor units.

If you go for 'central air' then you get a single outdoor unit (US folks often put them on the roof) but you then need to duct the air around.

With air you get no heat without a fan running, so there will always be some fan noise, although I suppose it's not do bad if the fan is at the far end of a duct. With water, the flow in the room can be silent (assuming the pump is mounted sufficiently far away). That's important if you want to sleep with it on, because some can't sleep with any fan noise.

Air2water heat pumps can heat your water too, which air2air can't.

Theo

[Paul]

One advantage of several outdoor units and split units on the inside, is redundancy. If one outdoor unit fails, the remaining outdoor units give at least some heat to the house. To resistively heat a house, while you wait for the replacement parts to arrive, can be very expensive.

It might well be cheaper to have just one outdoor unit, but that becomes a single point of failure.

And if the unit is going to leak, it will most likely be at the inside unit. The A-coils are a popular leak point. I've had the A-coil replaced on my central air. Only the old R12 units, "needed no maintenance". Everything modern is crap. And that's what scares me the most about modern heat pump equipment, is the perception it's not going to be reliable. Especially if they seriously start using CO2 as the working gas (really really high compressor pressure). If I had to make a gas choice, I'd prefer something flammable and lower pressure (R600a), than something like CO2. My kitchen refrigerator is flammable now :-)

I don't really know what the range of working gas choices is on heatpumps now, but it had better not be limited to CO2.

Paul

[williamwright]

It obviously would, but would it make enough difference to be worthwhile?

Bill

[RJH]

Depends what you mean by 'old'. English housing stock is old in terms of capacity to retrofit easily:

20% are pre-WW1. !5% of the stock built in the last 50 years.

[RJH]

Weird typo - c.25% in the last 50 years.

[Martin Brown]

Unlikely. The purpose of a fan assisted radiator is to drive air through a more complicated high surface area heat exchanger faster than it would flow by ordinary convection. They have to be properly designed.

Blow too hard and you will get more air out but it won't be warm enough to be as all useful. A toy PC fan and a couple of baffles to make the air take a longer convoluted path up the back of a radiator might work.

|___________ | | ___________| |___________ | | ___________| X fan

It is within the remit of DIY after all.

[NY]

No but they may have to retrofit a different *type* of central heating. People are changing over from oil/gas boilers that heat radiators with water at maybe 70 deg C to ground-source heat pumps that heat radiators with much cooler water (which need bigger radiators) or else using ducted air. It's a lot of effort to change that. One of our neighbour has just disfigured the side of his house with huge metal boxes with big (and noisy) fans which are something to do with a new central heating system.

My parents used to live in a house that was built in the early 70s - we were the first people to live there. The builder, in his infinite wisdom, had installed gas-fired ducted-air heating in all five houses in the development. It was crap: the house was always cold in winter and a lot of dust was blown around (probably disturbing dust that had fallen near the vents, rather than actually being blown through the ducts because the boiler had a fairly efficient dust filter which had to be kept clean). Mum was talking to the neighbour many years later, long after we'd left, and she said all five houses had changed over to gas-fired radiators at various times, and the amount of upheaval to retrofit 15 mm copper piping everywhere for radiators was tremendous.

[www.GymRats.uk]

I'd suggest the draught caused by any fan with enough flow to have any bearing on things would, by the nature of a draught make one feel colder even if the room temperature with or without fan was the same.

Cheers Pete

[David Wade]

but they can't cool, and I feel cooling is going to become critical for old un-fit fat people like me.

the also usually don't heat water as hot as other systems

Dave

[David Wade]

If you go for split units the work is minimal. One hole in the wall and one for power.

If they are high on the wall and there is more than one box, they will be ait source heatpumps, probably connected with wall mounted room units so air conditioning which can heat and cool.

If they keep him alive in the hot weather he probably thinks its worth the disfigurement of his house.

They should also improve his house energy efficiency rating which may allow him to actually sell it...

why 15mm. Surely for retro fit micro-bore is better Dave

[Martin Brown]

It has to be warm enough or there is a perceived and real cooling effect from evaporation off the skin from moving air. My office fan helps on a very hot day although it also blows loose paper about too!

It caused us trouble in the VH since the stupid electric wall heaters in Eco mode had a nasty habit of continuing to power the fan and modulating the heaters element on and off. When they were not actively emitting hot air they made the yoga class feel cold just through making air movement.

I have since nuked all "green" eco bollocks settings on them and have not had any further complaints about cold air.

[The Natural Philosopher]

You might suggest that, but in fact it needs remarkably little airflow over a hot surface to carry most of the heat away.

Convection alone is pretty good.

My fan blown rads are no way enough to cool anything. But when fed with hot water are pretty good at heating

[williamwright]

Slight changing of your ground there Rod, and it hasn't gone unnoticed. I said, "It obviously would, but would it make enough difference to be worthwhile?

But would it make enough difference to be worthwhile?

Just a figure of speech Rod.

But would it make enough difference to be worthwhile?

But not irrelevant to the fact that this is a DIY group.

Bill

[Theo]

They can, mine does. Vendors just delete that page in the UK manual because the UK 'doesn't do' cooling (and previously the RHI wouldn't pay for it), but it's easy to re-enable. It was one config parameter on mine.

To use the cooling usefully you need fan coil units, which are where we came in...

How hot do you want? Mine does 55C. It's good for a hot bowl of washing up. Other uses of domestic hot water mix down to lower temps anyway.

Theo

[Theo]

A church near me (barn-type place, built 1913) has ceiling fans up at the apex of the roof (maybe 12m high). I think the idea is they mix up the air so that the heat rising up gets blown back down at the occupants. I could imagine fan heaters doing the same in terms of distributing the existing heat across the room, rather than just blasting out heated air. But I agree they need to be sited correctly, and blowing air sourced from vents next to a concrete floor is not going to make it warmer.

Theo

[williamwright]

Liar.

Bill

[williamwright]

Don't believe you have one.

Bill

[The Natural Philosopher]

Yours will be assisted by an immersion heater then. barely possible to get over 35°C without

[williamwright]

No refutation available to you. So by switching to an irrelevance you demonstrate that you are flat out of arguments.

Bill

[williamwright]

Do people still wash the pots by hand? I had no idea.

Bill