Oversized rads a good idea?
- Thread starter wiffola
- Start date
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D
DeltaT2
Yes, but that'll have quite a high install cost, I'd just tee in the ASHP into the C/heating F&Rs & use a couple of NRVs & a couple of pipe thermostats. Ideally you should have a buffer tank.
That sounds very interesting indeed. We barely use any hot water and the boiler is very efficient when we do. For example, since Dec 2nd 2010 we've used 14 47kg cylinders. Since the heating went of March 23rd we've only had 2 new cyliders. That's a family of four with one mixer shower off the boiler.
Can you explain a little futher your proposed setup of this system please?
So we would keep LPG for DHW but tee ASHP into the central heating? How would i regulate between the ASHP and boiler to get max efficieny etc.
Would the ASHP get the heating to a certain temp and the boiler top it up?
If so can my ecotec combi do that? it's full modulating but not WRAS approved for preheated water.
Can you explain a little futher your proposed setup of this system please?
So we would keep LPG for DHW but tee ASHP into the central heating? How would i regulate between the ASHP and boiler to get max efficieny etc.
Would the ASHP get the heating to a certain temp and the boiler top it up?
If so can my ecotec combi do that? it's full modulating but not WRAS approved for preheated water.
J
JonasX
Air sourced are expensive and currently an expensive to run waste of time.
Oversized rads set to 60C reduce the boiler running temperature on a condensing boiler giving high efficiencies.
A weather compensator will be great on a condensing LPG or oil boiler as it keeps the flow temperature as low as possible matching the larger radiator's low temperatures.
Unless you go for water sourced or ground sourced heat pumps, it is best you get the most efficient condensing LPG/oil setup. This means heating the cylinder via a plate heat exchanger and bronze pump and not the inefficient internal coil. This can be retrofitted very easily.
Use weather compensation.
Use CH zoning, so say upstairs can be turned off most of the time.
Oversize the rads to run at 60C maximum.
Or use a thermal store with the CH taken off a coil in the cylinder. The boiler only heats the cylinder and highly efficiently at all times, far more than a direct rad system. The thermal store can be used if a ground sourced heat pump is used in the future. Futureproof the installation and make the system highly efficient right now, irrespective of the fuel used.
Oversized rads set to 60C reduce the boiler running temperature on a condensing boiler giving high efficiencies.
A weather compensator will be great on a condensing LPG or oil boiler as it keeps the flow temperature as low as possible matching the larger radiator's low temperatures.
Unless you go for water sourced or ground sourced heat pumps, it is best you get the most efficient condensing LPG/oil setup. This means heating the cylinder via a plate heat exchanger and bronze pump and not the inefficient internal coil. This can be retrofitted very easily.
Use weather compensation.
Use CH zoning, so say upstairs can be turned off most of the time.
Oversize the rads to run at 60C maximum.
Or use a thermal store with the CH taken off a coil in the cylinder. The boiler only heats the cylinder and highly efficiently at all times, far more than a direct rad system. The thermal store can be used if a ground sourced heat pump is used in the future. Futureproof the installation and make the system highly efficient right now, irrespective of the fuel used.
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Easiest solution to implement first would be. Leave the lpg boiler supplying the hot water for the house.
Add a buffer tank that is basically a tank with two flow and returns.
one pair connected to the air source, the other pair connected to the
lpg boiler. The air source pump is set to bring the buffer tank to a temperature say 50 degrees. A pump from the buffer tank feeds the central heating. A thermostat on the buffer tank if the tank temperature starts to drop below 50 degrees the lpg boiler is switched on and it will then heat the buffer tank back to the 50 at which point it switches off again leaving the air source doing the work. Hopefully most of the year
the air source would do all the work.
At a later date I would at an unvented hot water cylinder.
A another solution is as said T in both boilers into the central heating circuit. But this doesn't allow the air source heat pump to build up
a heat store until the central heating comes on. You could try
this solution first without the buffer tank.
Add a buffer tank that is basically a tank with two flow and returns.
one pair connected to the air source, the other pair connected to the
lpg boiler. The air source pump is set to bring the buffer tank to a temperature say 50 degrees. A pump from the buffer tank feeds the central heating. A thermostat on the buffer tank if the tank temperature starts to drop below 50 degrees the lpg boiler is switched on and it will then heat the buffer tank back to the 50 at which point it switches off again leaving the air source doing the work. Hopefully most of the year
the air source would do all the work.
At a later date I would at an unvented hot water cylinder.
A another solution is as said T in both boilers into the central heating circuit. But this doesn't allow the air source heat pump to build up
a heat store until the central heating comes on. You could try
this solution first without the buffer tank.
J
JonasX
Thanks - what are the pros and cons of not using a buffer tank?
Can you also explain how this setup would work. e.g. the heating is turned on at 20c on the thermostat and boiler is set to 60c. When the timer starts the heating, would this activate both the ASHP (say set to 50c) and then the lpg boiler to top it up to 60c?
Sorry I am a novice.
Can you also explain how this setup would work. e.g. the heating is turned on at 20c on the thermostat and boiler is set to 60c. When the timer starts the heating, would this activate both the ASHP (say set to 50c) and then the lpg boiler to top it up to 60c?
Sorry I am a novice.
***********
Thanks - what are the pros and cons of not using a buffer tank?
Can you also explain how this setup would work. e.g. the heating is turned on at 20c on the thermostat and boiler is set to 60c. When the timer starts the heating, would this activate both the ASHP (say set to 50c) and then the lpg boiler to top it up to 60c?
Sorry I am a novice.
**************
If you are using a buffer tank but the demand from the central heating
is greater than the air source can supply it allows the air source heat pump
to build up a store of heat therefore smoothing out the demands from the
central heating. The main advantage of not using one is it is cheaper and less space is needed.
Note a heat pump can usually supply up to about 55 degrees. Some quote higher figures but only achieve this with immersion heaters.
Either way whether using a buffer tank or not you would set the heat pump
to come on at say 6am and the lpg boiler to come on at 6.30am. The thermostat for the lpg boiler would be set slightly lower. If the air source heat pump has met the demands the lpg boiler won't kick in at 6.30am.
If the temperature of the central heating hasn't reached temperature the lpg will kick in and bring the central heating up to temperature then cut out until called on again.
Check out the manuals for the trianco activair units they give a few example installations arrangements and performance figures for their units.
Thanks - what are the pros and cons of not using a buffer tank?
Can you also explain how this setup would work. e.g. the heating is turned on at 20c on the thermostat and boiler is set to 60c. When the timer starts the heating, would this activate both the ASHP (say set to 50c) and then the lpg boiler to top it up to 60c?
Sorry I am a novice.
**************
If you are using a buffer tank but the demand from the central heating
is greater than the air source can supply it allows the air source heat pump
to build up a store of heat therefore smoothing out the demands from the
central heating. The main advantage of not using one is it is cheaper and less space is needed.
Note a heat pump can usually supply up to about 55 degrees. Some quote higher figures but only achieve this with immersion heaters.
Either way whether using a buffer tank or not you would set the heat pump
to come on at say 6am and the lpg boiler to come on at 6.30am. The thermostat for the lpg boiler would be set slightly lower. If the air source heat pump has met the demands the lpg boiler won't kick in at 6.30am.
If the temperature of the central heating hasn't reached temperature the lpg will kick in and bring the central heating up to temperature then cut out until called on again.
Check out the manuals for the trianco activair units they give a few example installations arrangements and performance figures for their units.
Check out Richard Owens posts...
http://www.navitron.org.uk/forum/index.php/topic,7926.0.html
Maintains a buffer exacerbates heat pump compressor cycling!
http://www.navitron.org.uk/forum/index.php/topic,7926.0.html
Maintains a buffer exacerbates heat pump compressor cycling!
J
JonasX
"exacerbates heat pump compressor cycling"?
Where did you get that? He wrote. "If the heat pump is working at the capacity of the heating system, then there's no need for a buffer tank."
If the heat pump is working over the capacity of what the heating system can draw out, it will cycle - as do boilers 90% of the time. The heat pump needs a buffer to stop this cycling. If say the heating system is drawing just 2 kw of heat and a 3 kw heat pump is giving 6kW (COP 2) then it will cycle and needs a buffer to store that heat. Simple.
Buffers, and thermal stores which are buffers, even out supply and demand.
D
DeltaT2
I hate to agree with you Water Systems, but you're correct the ASHP will cycle like hell. However, the OP is on a tight budget, so a buffer tank is something he can't afford. So it can be installed without, not the best, but it can be done.
J
JonasX
This Cowboy man again.
It is not my water system. Fitting a heat pump without the buffer is false economy. The same for boilers as well, this where thermal storage scores very highly and vastly underrated and misunderstood. Unless the boiler can modulate right down under 1 kw, like the Geminox, then a buffer, thermal storage, is not needed.As Heat pumps do not modulate, a buffer tank is essential. Richard Owens on Navitron got it wrong. He is assuming the demand will always be higher than the supply by the heat pump. If this is the case, then you do not need a buffer. But houses warm up and demand drops like stone when that happens and then the buffer comes into its own.
The better quality air con and heat pumps do modulate.
They do this by changing the speed of the compressor.
They do this by changing the speed of the compressor.
J
JonasX
I believe these are stepped rather than full modulation.
D
DeltaT2
Do you mean inverted? They cost a fortune, 25-30 years pay-back!!!
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