Huge radiators and single pipe gas boiler, heat pump work?

wrf12345

Thinking of buying a house that has an ancient gas boiler that I will be capping off as too dangerous to use, connected to huge double row radiators but running on a single pipe so the lounge (first rad) will be warm whilst the second bedroom is at the end and probably not going to get very warm, the pipework runs in the basement garage so can be sussed. Just wondering if you can get away with connecting an air to water heat pump to the system (the hot water would remain electric as not used much if at all by myself), not too worried about the rooms not being the same temperature as can shuffle my use in winter to get the max benefits from the warmest room and it is actually very unhealthy to sleep in a warm bedroom.

Netexporter

Even if the radiators are big enough the pipework will have to be changed to normal 2-pipe flow and return. That water only circulates through the rads by convection, so nowhere near enough heat will be transferred. Modern radiators with sufficient output will be much smaller.

michaels

Not sure, with TRVs less and less flow would go into each room as it gets up to temp pushing more warm flow to the next room - because the heat pump runs continuously rather than in bursts this process should complete so that even the farthest room gets enough heat?

Reed_Richards

If the radiators are connected in series and you pump water around them fast enough so that there is only a few degrees of temperature drop across each radiator then it might work for you.  But I don't think you would find a plumber who would let you do that; it would have to be DIY.

matt_drummer

wrf12345 said:

Thinking of buying a house that has an ancient gas boiler that I will be capping off as too dangerous to use, connected to huge double row radiators but running on a single pipe so the lounge (first rad) will be warm whilst the second bedroom is at the end and probably not going to get very warm, the pipework runs in the basement garage so can be sussed. Just wondering if you can get away with connecting an air to water heat pump to the system (the hot water would remain electric as not used much if at all by myself), not too worried about the rooms not being the same temperature as can shuffle my use in winter to get the max benefits from the warmest room and it is actually very unhealthy to sleep in a warm bedroom.

How do you know the rooms at the end will be cooler?

The water may well be cooler, but as I have tried to explain to you before, heat does not come from the temperature of the water, it is the change in temperature.

If the radiators were sized appropriately you could get exactly the same temperature in the rooms at the beginning and end of the run.

Single pipe systems will work fine with an air to water heat pump. As long as the water goes back to the heat pump cooler than it leaves all is well. The heat pump has no idea what you have connected it to.

Ignore the comments about trvs.

You can't have trvs if the radiators are plumbed in series for the obvious reason!

matt_drummer

You won't get the grant, again for the obvious reasons.

michaels

matt_drummer said:

wrf12345 said:

Thinking of buying a house that has an ancient gas boiler that I will be capping off as too dangerous to use, connected to huge double row radiators but running on a single pipe so the lounge (first rad) will be warm whilst the second bedroom is at the end and probably not going to get very warm, the pipework runs in the basement garage so can be sussed. Just wondering if you can get away with connecting an air to water heat pump to the system (the hot water would remain electric as not used much if at all by myself), not too worried about the rooms not being the same temperature as can shuffle my use in winter to get the max benefits from the warmest room and it is actually very unhealthy to sleep in a warm bedroom.

How do you know the rooms at the end will be cooler?

The water may well be cooler, but as I have tried to explain to you before, heat does not come from the temperature of the water, it is the change in temperature.

If the radiators were sized appropriately you could get exactly the same temperature in the rooms at the beginning and end of the run.

Single pipe systems will work fine with an air to water heat pump. As long as the water goes back to the heat pump cooler than it leaves all is well. The heat pump has no idea what you have connected it to.

Ignore the comments about trvs.

You can't have trvs if the radiators are plumbed in series for the obvious reason!

I thought with a single pipe system each rad was a shunt in parallel to the single pipe



So water is colder in each successive rad as warm flow is 'diluted' with colder water coming from the rads it has already passed - but as the first rad gets up to temp the TRV reduces the flow through it so less cooling before the second rad etc and with a continuous warm flow from a heat pump rather than a cycling boiler it is likely that the rooms will be more even in temp than with a bioler.

Plus as suggested the level of heat emitted depends on both the delta T and the size of the rad so the end room rads could be larger supporting the same heat discharge from a lower deltaT.

matt_drummer

You may be correct, but who knows how it is plumbed.

Your diagram looks more sensible I must admit.

Still, I don't like trvs with heat pumps.

But, I apologise, they may not have the consequences I was suggesting if plumbed as shown.

The heat pump is just a heat source like the boiler.

The key as always is how low the heat pump can modulate, generally you need as much emitter capacity as possible.

As you demonstrate though, no reason why it wouldn't work and it is entirely feasible to get adequate heat into all rooms with a single pipe system.

Obviously, if the radiators are plumbed in series then trvs are a no go.

wrf12345

Thanks, no TRVs and the rad's are indeed in series, done at a time when there were no rules other than for the gas boiler bit (almost an antique), the radiators were designed for a house with zero insulation and single pane windows, both of which have been upgraded - in wall insulation, roof insulation and fairly recent double glazing, though personally I would have bricked up half the non-south windows but would be a pity to "wreck" the existing ones. I quite like the simplicity of the design, the only worry that it will survive the flow rates needed for heat pump efficiency. With the grant I suspect they will want a complete replacement of everything and it will be a lot more than 7.5k by the time they have finished installing an unwanted hot water system as well but I will give it a try if I go ahead with the purchase (for my own use not rental, which doubtless has additional rules coming). 

Reed_Richards

You may intend to stay in this new house forever but we don't live forever and sooner or later somebody else will want to live there.  So if you have an opportunity to a major refurbishment, possibly grant assisted, then you ought to give some regard to what others will want, not just yourself.  Many others would deem a supply of hot water necessary, even if you don't.  For that reason I'm pretty sure that if you got that £7.5k grant, you would be obliged to install a hot water system that you, personally, don't want.

matt_drummer

wrf12345 said:

Thanks, no TRVs and the rad's are indeed in series, done at a time when there were no rules other than for the gas boiler bit (almost an antique), the radiators were designed for a house with zero insulation and single pane windows, both of which have been upgraded - in wall insulation, roof insulation and fairly recent double glazing, though personally I would have bricked up half the non-south windows but would be a pity to "wreck" the existing ones. I quite like the simplicity of the design, the only worry that it will survive the flow rates needed for heat pump efficiency. With the grant I suspect they will want a complete replacement of everything and it will be a lot more than 7.5k by the time they have finished installing an unwanted hot water system as well but I will give it a try if I go ahead with the purchase (for my own use not rental, which doubtless has additional rules coming). 

High flow rates are not necessary for an efficient heat pump installation.

Mine flows water at 6.5 lpm, it's very low but also very efficient.

Heat delivered is the product of dT between flow and return and the flow rate. So you can have a low dT and a high flow rate or vice versa and anywhere inbetween and get the same result. All that matters is the emitters capacity to deliver heat.

You say huge radiators, what does that mean?

If they are old non convector radiators they won't put out as much heat as new convector radiators of the same size.