Which type of boiler and system for our situation....

[ajrobb]

The static pressure of the water is not enough information to tell you how many showers can run at the same time. You might need to consider upgrading the water supply if it is ½".

As mentioned, you could consider a bronze pump to circulate hot water from a cylinder to all the rooms and prevent wasting water running taps to get them warm. The hot pipes would need to be well insulated.

 

[abbadon]

Ok, so wind forward a few months, and we have made some progress/decisions and found some other tradesmen to make their suggestions. We have also confirmed the requirement for a better mains supply - the current pipe is 80 ish yards from road and is a 20mm pipe - but we only get 12l/min at house at 4.4 bar, upgrade is going to be to 32mm and hopefully get us a lot closer (maybe approaching 22-25l/min)to the flow rate at the road (30l/min measured at main in road)

We are now at the point of having pretty much settled on a thermal store, likely a Gledhill 250 litre multifuel OV, a Worcester Bosch 40cdi conventional boiler, all installed in the loft.

However I want to check with people here as this is where I have a slight difference on opinion to the plumber - he wanted to go for a system boiler and the version of the store with a heat exchanger in the boiler loop as he thinks we cant get enough head on the boiler if its in the loft - but I have read on the Bosch website that only 0.25m minimum is needed above the highest point in the heating system (the boiler and store in our case) and we have a very high loft so should easily be able to accommodate that even above the thermal store (2m high itself).

Does this make sense - am I right in thinking that small head is all thats required for a feed and expansion tank for the overall boiler/store/radiator system as a whole?

The main reasons I would rather go conventional rather than system are

a. To allow direct connection of boiler to store, and the efficiency benefits this brings.
b. to allow us to fit 2 or 3 immersions as a backup to allow both DHW and heating to run from these in a boiler failure situation (this cant be done if the boiler heats the store via a coil obviously and you need a coil if using a system boiler as he has described)
c.Allow us to "dump" the stores heat to radiators if desired for quick heat up (again isn't possible if the boiler has a coil in its loop to the store)

looking forward to hopefully the final piece in our puzzle.

Andy

 

[ironman1]

- but I have read on the Bosch website that only 0.25m minimum is needed above the highest point in the heating system (the boiler and store in our case) and we have a very high loft so should easily be able to accommodate that even above the thermal store (2m high itself).

I would be inclined to fit a sealed system utilising unvented HW storage...............low system head can cause many issues when coupled with high resistance heat exchangers , THINK AGAIN.

To be honest , if my customers haven't 100% faith in me then i've lost the battle before the contract is even started.

 

[abbadon]

Hi,

I am unsure why the head and the heat exchanger should be a major factor - we are talking a thermal store which utilises mains hot water - so the only water that needs to pass through a heat exchanger is being forced there by mains pressure?

The F and E tank will only be to maintain level/allow expansion in the vented system, i.e. boiler/store tank/radiators.

Can you elaborate more?

My other concern with moving to a pressurised rad loop is the integrity of older joints in the house and whether its safer to stick with vented rads to avoid issues?

Andy

cheers

Andy

 

[ironman1]

Hi,

I am unsure why the head and the heat exchanger should be a major factor - we are talking a thermal store which utilises mains hot water - so the only water that needs to pass through a heat exchanger is being forced there by mains pressure?

The F and E tank will only be to maintain level/allow expansion in the vented system, i.e. boiler/store tank/radiators.

Can you elaborate more?

Most all boilers now use high resistance heat exchangers , static head between F&E cistern & boiler heat exchanger in your example would be pretty low , say under .5 metres? , positive/negative pressures will occur @ some point between boiler HeX & thermal store depending on circulator positioning , this can make way for cavitation/air ingress...............this makes for a poorly designed system ............much better ways of designing the system in question.................when dealing with low static heads & high resistance heat exchangers then the best way forward would be to pressurise the system............the .25 metre your refering too would be between highest point of circuit to underside of F&E cistern NOT .25 metres between circulator/F&E...............listen to your engineer...........good luck.

EDIT...reason.. spelling mistakes.

 

[ironman1]

Hi,


My other concern with moving to a pressurised rad loop is the integrity of older joints in the house and whether its safer to stick with vented rads to avoid issues?

Andy

cheers

Andy

If you are converting the property to a bed & breakfast then i would 'assume' all pipework & radiators would be replaced?....for 'piece of mind'?