Domestic hot water system options

[denners]

Hi all


I've been looking at options for replacing our knackered old gas boiler with Y plan gravity fed central heating / hot water system and could do with some advice. We are in a 3 bed (2 person) mid terrace, only 1 bathroom but we like a good shower and don't fancy electric shower or combo boiler for this reason, but also want rid of the tanks in the loft (to reduce water damage risk and free up valuable space). The hot water cylinder (120 litres), pump and mid position valve are all in the same place (airing cupboard) so I'm hoping that we can make reasonable changes to the system without ripping up floors/walls etc. Mains water pressure is high and water is soft here so no worries there. I am also interested in the possibility of adding solar thermal possibly now, but at least leaving the option to add it at a later date to whatever system we put in now.


So I've been reading around and had a couple of quotes, and our options seem to be:


1) Unvented cylinder (120litre ish megaflow or similar) for DHW, and convert CH system to mains fed (would need a small 10litre ish expansion vessel)
Advantages:
Several plumbers around here (Ayrshire) are used to them and could fit them!
Better flow rate for hot water?
Simpler replacement for current system?
Disadvantages:
Less efficient use of solar thermal?
Requirement for annual inspection
The thought of having something potentially explosive (yes I know this is unlikely) in the airing cupboard


2) Small (120-150litres) heat bank for DHW with CH system as for (1)
Advantages:
More efficient use of solar?
More efficient use of heat generally through stratification and allowing the new boiler to fire for longer periods rather than frequent short bursts?
Not pressurised
Disadvantages:
Slightly more expensive to fit than (1)
Smaller heat banks (to suit our needs) less efficient than larger heat banks?
Reputation for building up sludge?
I'm having trouble finding a heating engineer/installer in the area that has experience with them...


3) Slightly larger (maybe 150-200litres) heat bank for DHW and CH (probably direct feed to CH to make use of single F&E tank, which means system and radiators will need a good flush!)
Advantages:
As for (2) plus potential use of solar for CH and end up with simpler system?
Disadvantages:
As for (2) plus slightly more complicated to convert existing setup?


Based on my (limited) knowledge, I'm leaning towards option (3) as it seems the most elegant and long term most efficient / cheapest to run. But there seems to be some very strong opinions (pro and con) re heat banks floating around and I'm not sure what to believe.... So my questions are:


Does this summary seem reasonable? Anything you disagree with?


Given that I am changing the boiler at the same time, am I better to go with a closed system boiler and indirect feed to the tank or vented system boiler and direct feed to the tank for option 3 (I assume condensing boiler on sealed system is better for options 1 and 2)?


Any positive or negative experiences with heat banks or unvented cylinders that you would like to share?


Can anybody recommend a good heat bank system with solar, gas and immersion heater connections that will drive DHW and CH (it looks like external plate heat exchanger systems are better for DHW, but advice welcome)?


Is any particular boiler type best for this system?


Can anyone recommend someone (or themselves!) to supply and install this system (+/- solar thermal depending on cost) in the Glasgow area?


Any advice greatly appreciated!


Thanks,


Matt

 

[phpaul]

Hi all


I've been looking at options for replacing our knackered old gas boiler with Y plan gravity fed central heating / hot water system and could do with some advice. We are in a 3 bed (2 person) mid terrace, only 1 bathroom but we like a good shower and don't fancy electric shower or combo boiler for this reason, but also want rid of the tanks in the loft (to reduce water damage risk and free up valuable space). The hot water cylinder (120 litres), pump and mid position valve are all in the same place (airing cupboard) so I'm hoping that we can make reasonable changes to the system without ripping up floors/walls etc. Mains water pressure is high and water is soft here so no worries there. I am also interested in the possibility of adding solar thermal possibly now, but at least leaving the option to add it at a later date to whatever system we put in now.


So I've been reading around and had a couple of quotes, and our options seem to be:


1) Unvented cylinder (120litre ish megaflow or similar) for DHW, and convert CH system to mains fed (would need a small 10litre ish expansion vessel)
Advantages:
Several plumbers around here (Ayrshire) are used to them and could fit them!
Better flow rate for hot water?
Simpler replacement for current system?
Disadvantages:
Less efficient use of solar thermal?
Requirement for annual inspection
The thought of having something potentially explosive (yes I know this is unlikely) in the airing cupboard


2) Small (120-150litres) heat bank for DHW with CH system as for (1)
Advantages:
More efficient use of solar?
More efficient use of heat generally through stratification and allowing the new boiler to fire for longer periods rather than frequent short bursts?
Not pressurised
Disadvantages:
Slightly more expensive to fit than (1)
Smaller heat banks (to suit our needs) less efficient than larger heat banks?
Reputation for building up sludge?
I'm having trouble finding a heating engineer/installer in the area that has experience with them...


3) Slightly larger (maybe 150-200litres) heat bank for DHW and CH (probably direct feed to CH to make use of single F&E tank, which means system and radiators will need a good flush!)
Advantages:
As for (2) plus potential use of solar for CH and end up with simpler system?
Disadvantages:
As for (2) plus slightly more complicated to convert existing setup?


Based on my (limited) knowledge, I'm leaning towards option (3) as it seems the most elegant and long term most efficient / cheapest to run. But there seems to be some very strong opinions (pro and con) re heat banks floating around and I'm not sure what to believe.... So my questions are:


Does this summary seem reasonable? Anything you disagree with?


Given that I am changing the boiler at the same time, am I better to go with a closed system boiler and indirect feed to the tank or vented system boiler and direct feed to the tank for option 3 (I assume condensing boiler on sealed system is better for options 1 and 2)?


Any positive or negative experiences with heat banks or unvented cylinders that you would like to share?


Can anybody recommend a good heat bank system with solar, gas and immersion heater connections that will drive DHW and CH (it looks like external plate heat exchanger systems are better for DHW, but advice welcome)?


Is any particular boiler type best for this system?


Can anyone recommend someone (or themselves!) to supply and install this system (+/- solar thermal depending on cost) in the Glasgow area?


Any advice greatly appreciated!


Thanks,


Matt

just fit a 35kw viessman combi they give 15 lts per min with a 45 deg rise more flow with less rise and cost a grand inc flue and vat
get a new water main

with the left over budget fit solar pv to ur roof the payback on solar thermal is rubbish

 

[phpaul]

if ur real worried about the best performance verses all other factors i would say u need to totally re pipe the place use under floor heating or over-sized rads to give the boiler a low flow temp on the ch flow . the big rads dump the heat into the room quickly and less gas is burned and insulate under floors and all under floor pipes ex the gas .

 

[dennis2011]

We had fitted a 150 litre DPS Heatbank fitted about 4 years ago by a local plumber. First one he had fitted - looked at specs and fitting instructions - was confident to do work and quoted. He said he was always prepared to learn and try something new, how refreshing! (One other plumber even refused to quote - obviously he had not understood the concept of a heatstore - said he hadn't got the certification to fit a pressurised cylinder!!)
Anyway, We had one fitted with 2 plate heat exchangers, one on the input side and one on the output side. The one on the input side is instead of a more usual indirect cylinder, referred to by DPS as rapid recovery system. Our 28kw gas boiler can heat the whole tank from cold in 35 minutes. The heatbank took him two days to install. We have 2 bar mains but only 15mm feed. Would have had to rip up kitchen to install 22mm feed. But plumber did flow test first in airing cupboard and we were getting 18 litres per minute which was good enough for me to go ahead. No problems with the installation apart from the fact that there was an error on the wiring diagram supplied by DPS which took a couple of hours to sort out. We can use two showers at same time - no problem. Our airing cupboard in central in our house so would be very difficult to have unvented pressured cylinder due to diificulties routing the discharge pipe. Also I was not happy with the safety aspects of a pressurised tank of hot water or the need for annual service. I have recently fitted a short 750w immersion heater so I can use my surplus solar electricity to save a bit of gas. Very pleased with instalation. We can safely drink our hot water as it is not stored but just heated as it passes through the output heat exchanger.