ie as soon as you turn the tap on. i read some time ago that some hw systems were designed to allow natral constant flowing of hot water through the pipes in order to gurantee hot water instantly at any tap in the house. i know its likly to be energy inefficent...but ...id still like to know how to do it!
You can get bronze circulating pumps that do this. Basically you put in an extra (small) pipe in parallel with the normal one and create a small circuit, with the taps coming off of the main run.
Grundfos make them.
Regarding energy efficiency, when it's used at the same time as the heating in the house and the hot water is heated in the same way, it doesn't make a lot of difference.
How it works? A combi boiler heats water just like a normal boiler by its gas to water heat exchanger. It has a pump which diverts the heated hot water (primary water, that is the water in the radiators) through a water to water plate heat exchanger, which transfers the heat from the primary water to the cold incoming secondary water (secondary is fresh water). Hence, cold water coming in from the water mans is instantly heated. There is a small lag at the taps while the boiler warms up. This is overcome in some models by pre-warming the water to water heat exchanger or incorporating a small preheated water vessel.
i know how a combi works...but it is not instantly available at the taps is it? apparently in the old early victorian ch systems, hot water was constantly circulated through the pipes by convection only ie instantly hot when you turn the tap on!
No, I was careful to say "when it's used at the same time as the heating".
Think of it this way. Radiator/UFH system is connected to boiler, water is circulated and the emitters are designed to deliberately emit heat. Boiler also heats hot water in cylinder. Separate small circuit with small pump circulates water from cylinder and emits some heat into the same space (i.e. the insulated envelope of the house) as the radiators/UFH. In effect the HW loop contributes to the house heat. Since the energy to do so costs the same each way, the efficiency is broadly the same.
If this HW circuit were run in places which would be unheated then the efficiency would be less, but OTOH, they would also be highly insulated.
Obviously in the summer when the house is not heated, it can be argued that more heat is being released than otherwise would be......
By "constant", it appears he really meant constant, not just when the hot tap is turned on. Admittedly the English wasn't perfect and left open to misinterpretation.
A combi can give infinitely continuous hot water. Many commercial kitchens would have one or two multi-points as the taps were virtually on continuously. A storage cylinder would have to be very large and take up space to compete with the level of continuous water required.
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