pressurised domestic water system advice sought

thetourist

hi - am building a new house and incorporating a ground source heat pump and underfloor heating -- the company suggested that we put in a pressurised system so that there is no tank in the attic and there is no need for thermostatic mixer valves on the showers etc - has anybody any opinions about these - esp if someone can give some idea of how they compare pricewise with a standard system

thanks
bob

Victor

Two separate issues:

1. Heating system to heat the house
2. Hot water system for showers, baths, sinks, etc.

Ideally place your boiler / heat exchanger and hot water tank as central as possible in the house - shoter pipe runs and less heat loss from the boiler and the hot pipes. Ideally place bathrooms and kitchens in clusters (the fewer the better).

1. Having the heating system, pumped means that the far corners of the system will be heated much better, as they get hot water, not whatevers "left over". Good in a very big house.

2. Regarding the hot water system, you can have a "flow and return" arrangement where hot water is continuously pumped around the system, so that you have hot water "on tap" - immediately (1-2 seconds, not 1-2 minutes). The downside of this is, as the water is being pumped around, it is loosing heat. Bad in a very big house.

Installing the pumps shouldn't cost more than a few hundred euros each, with a little more piping and wiring (the expansion vessel at the boiler replaces the expansion tank in teh attic), but they provide a good system. The downside is it will cost a bit more to install and run.

pipers

Unvented (Pressurised) plumbing systems are excellent.


Benefits are:

Equal pressure at all fixtures (showers especially), however you may still require thermostatic showers.

With the aid of a secondary return pump, there are no dead legs. There is more pipework involved but this acts as additional hot water storage.
The storage tanks can be situated any where.
No airlocks.

However the pump is a monster and noisy so it should be sited outside in a garage or boiler house, not indoors. You will need a more powerful boiler in order to reheat the cylinder, which takes about 20 minutes.

Have a look here for more details of unvented cylinders.



It will cost more to install, but the system will pay for itself on energy costs.

Victor

Originally posted by pipers
There is more pipework involved but this acts as additional hot water storage.

Hardly, very inefficient heat loss wise and 10m of pipework will only hold 3 litres of water

pipers

The secondary return circulation also ensures that the water in the cylinder heats up more efficiently, at a uniform temperature.

Whereby if it is not circulated, it's heated by gravity there is a significant difference between the temperature at the top (hot) and at the middle (tepid) as hot water will always rise.

Victor

Originally posted by pipers
The secondary return circulation also ensures that the water in the cylinder heats up more efficiently, at a uniform temperature.

Fine if you are having a bath, but not if you just want to leave the system at "sink". Potentially it means you have a huge amount of warm water and no hot water.

When you (pipers) do a flow and return, do you put the return in at the bottom with the cold feed or do you put it further up?

pipers

Its normally a third to half way down the cylinder.

thetourist

if anyone can answer some of these questions then i would be grateful

i read in a diy book that one disadvantage to an unvented (pressurised) system is that there can be growling when the water is trying to negotitate sharper bends in the pipework -- is there any truth in this

also can anyone advise me
i am building a house and would like to consider a pressurised system -- if i get a builder then he would have his own plumber -- the question i have is this -- would a typical plumber be able to deal with this type of system or would i have to pay close attention to which plumber the builder employs - or even stipulate in the spec list that i want a particular plumber -- i am reluctant to do the latter because it could mean a delay in waiting for "my choice" of plumber

also i am putting in a ground source heat pump to service underfloor heating - are there any issues in using this type of setup with an unvented system

lastly can anyone give me like a percentage over and above a typical system -- eg an unvented being x% more expensive than a vented or something like that ??

Victor

Originally posted by bobmurphy
i read in a diy book that one disadvantage to an unvented (pressurised) system is that there can be growling when the water is trying to negotitate sharper bends in the pipework -- is there any truth in this

I don't think it's a material problem. In the apartment I used to live in, the system used to grumble once or twice a day - nothing to keep you awake at night.

Originally posted by bobmurphy
i am building a house and would like to consider a pressurised system -- if i get a builder then he would have his own plumber -- the question i have is this -- would a typical plumber be able to deal with this type of system or would i have to pay close attention to which plumber the builder employs - or even stipulate in the spec list that i want a particular plumber -- i am reluctant to do the latter because it could mean a delay in waiting for "my choice" of plumber

I imagine the vast majority of plumbers would be able to do it, if he can't manage one particular part, he'll just hire one of his mates for the day that can.

Originally posted by bobmurphy
also i am putting in a ground source heat pump to service underfloor heating - are there any issues in using this type of setup with an unvented system

I imagine all underfloor systems are pumped and unvented.

Originally posted by bobmurphy
lastly can anyone give me like a percentage over and above a typical system -- eg an unvented being x% more expensive than a vented or something like that ??

The only real extra cost would be the pump(s) (a few hundred euros each) one for the heating system, one for the hot water system (this also needs extra pipe work, maybe an extra €100-200 per hot tap / shower). Again trying to cluster all your bathrooms / kitchen together will reduce the cost (see sketch).

pipers

an unvented cylinder and associated pumps controls will cost from 1500 euro up (supply only) depending on the demand and size of property

A traditional cylinder will cost a lot less, in the hundreds.
However when you start adding shower mixers, valves & pumps etc, the price gap narrows signifigantly.

Regarding noise in this sytem, its not an issue.

A ground source heat pump may not have the output to satisfy the requirements for the unvented cylinder as it has a recovery time of 20 minutes, which places a massive demand on a boiler. It may be worth considering a dedicated boiler for the hot water.

A competent plumber will be able to install this type of system.

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mfenton

Hi guys,

I'm thinking of heat pump for a new house build. I'm considering the options for the collector and one particular supplier is pushing a bored well water to water heat pump over the horizontal collector. Apparently, as the temperature of the well water would lend itself to a greater COP (12C well water - 6.5 COP). Two other heat supplier companies are set against this system - they think that it is too much trouble installing, requires far more maintenance, higher costs for drilling etc (although my thinking is that I'll be boring a well anyway) and there are risks of water contamination. The reasons why I'd opt for the bored well heat pump is that I would expect this costs to be lower given that there would be no site excavation as there would be for the horizontal collectors.

What do ye think? I went back to the first supplier and he claims that these companies are simply just trying to sell more pipe etc. This supplier is heating his 6100 sq ft house with one bored well heat pump. I did visit another installation and he was quite happy with the system - installed 2005.

This supplier also claims that aluminium rads (sized for 40C) would keep the electricity running costs lower that that for under floor whereas the other companies say the under floor is better. In any case I will at least go for under floor in part of the house as I have reduced space for rads.

Any thoughts are appreciated.

Cheers,
Martin