Plumbing in a heat exchanger

[Dman2]

Have a heat exchanger fed from biomass doing blow heaters in workshop.
Want to add a hot water tap,
If I plumb a second heat exchanger in should it be in parallel or series?

Will put a blending valve in as well so dont get scalded

Cheers

 

[Still Farming]

Is sealed and open vented issues for this tap on it maybe ?

 

[Turra farmer]

For something as minor as a tap paralell would be simplest

 

[Doing it for the kids]

I would T it off before the heating exchange to get first dips on heat.

May need a low delta if you want the hottest water you can get though

 

[Ukjay]

Have a heat exchanger fed from biomass doing blow heaters in workshop.
Want to add a hot water tap,
If I plumb a second heat exchanger in should it be in parallel or series?

Will put a blending valve in as well so dont get scalded

Cheers

Just curious, but do you have any drawings of your proposal - you may or may not know this, but the one thing you need to be very careful of is that you do not want to create yourself an Unvented System with no Safety Circuit built in.

There is a serious risk that someone could get seriously hurt if the water went over pressure / then over temp (100 degrees), and then someone opened a tap unknowingly - as the outflow would not be water, it would be steam that would expand immediately upon opening the outlet (iirc, approximately 1600 times the volume of water), scalding the person using it and the blending valve would not stop that from happening unfortunately.

 

[Dman2]

Just curious, but do you have any drawings of your proposal - you may or may not know this, but the one thing you need to be very careful of is that you do not want to create yourself an Unvented System with no Safety Circuit built in.

There is a serious risk that someone could get seriously hurt if the water went over pressure / then over temp (100 degrees), and then someone opened a tap unknowingly - as the outflow would not be water, it would be steam that would expand immediately upon opening the outlet (iirc, approximately 1600 times the volume of water), scalding the person using it and the blending valve would not stop that from happening unfortunately.

Will put a drawing up later today for you all to laugh at

 

[Dman2]

Here are 2 rough sketches 1st one is existing set up

 

[Ukjay]

Will put a drawing up later today for you all to laugh at

I doubt anyone would laugh - it is simply to understand what you plan, because water under pressure can be superheated, which basically means you can increase the temperature above 100 degrees c, where it usually turns to steam.

 

[Ukjay]

Here are 2 rough sketches 1st one is existing set up
View attachment 609862
View attachment 609864

OK - so what safety devices are on the existing system for the fluid circulation side, and what fluid is in it?

 

[chickens and wheat]

My chicken shed heaters are all plumbed in parallel, Why add a tap? it will just require more water adding to the system with more O2 iron calcium whatever, just tape/cable tie a water pipe to the hot pipes, That should give you a good amount of hot water with reasonable time between tap openings.
That way some muppet cant leave the tap on also.

 

[Dman2]

OK - so what safety devices are on the existing system for the fluid circulation side, and what fluid is in it?

Hot water is fed from a buffer tank with temps set at 70 oC
on the output side of the heat exchanger, there is an expansion vessel with a PRV and filling loop, these feed 2 blow heaters.
My plan was for a second small heat exchanger to feed a hot water tap for filling calf buckets etc.
With a blending valve to regulate temperature.
The hot water feeding the system is regulated in the boiler room at the buffer tank, so should not get any steam problems at the output end?

 

[TripleSix]

I would plumb in your small heat exchanger before your workshop heaters and I'd be tempted to have a small mains fed header tank up on the wall to feed your tap via gravity.

Thus you don't create a sealed system.

Plumb into a mixer tap with the cold fed from the header too and they'll both run at the same rate.

Look for a scrap combi boiler for a cheap heat exchanger.

 

[Dman2]

I could just put a pressure reducing valve in the line
Not got much height for a header tank

 

[Ukjay]

Hot water is fed from a buffer tank with temps set at 70 oC
on the output side of the heat exchanger, there is an expansion vessel with a PRV and filling loop, these feed 2 blow heaters.
My plan was for a second small heat exchanger to feed a hot water tap for filling calf buckets etc.
With a blending valve to regulate temperature.
The hot water feeding the system is regulated in the boiler room at the buffer tank, so should not get any steam problems at the output end?

OK - so if I understand this correctly, the main pipework has a closed loop system that is not for drinking - only for providing heat output via the blow heaters. This circuit is controlled by all the required safety devices to prevent overheating etc - so all good.

On this basis - your idea is a way for you to utilise the existing network of pipes to give you the hot water feed you require. Just ensure that you understand the size of the current expansion vessel, because if you add too much pipework etc, and the extra water content puts the net volume over the specified unit currently on - you may get the valves letting the water out as the system heats up, then you may require a larger volume expansion vessel.

Series HE can work, but parallel is a better option imho.

I assume you planning on taking the new hot water feed from the Buffer tank, if so - you should also take the cold feed to the valve too - with the hot feed lower in the buffer tank than the cold feed, as this then shuts the hot water feed off first if there is a problem with the header tank running out.

 

[Dman2]

yes main pipework is existing closed heating system
i am only going to be adding @ 2m pipework + exchanger to existing.
Planning on utilising existing feed from buffer and just adding a second HE to keep tap water separate from heating

 

[B R C]

Is the feed from buffer an open system? Are you allowed to plumb mains water supply straight through heat exchanger, maybe a non return valve should be added? I want to do the same so would like to know! My work shop blowers fed directly from open vented buffer tank though. House system has heat exchanger though.

 

[Ukjay]

Is the feed from buffer an open system? Are you allowed to plumb mains water supply straight through heat exchanger, maybe a non return valve should be added? I want to do the same so would like to know! My work shop blowers fed directly from open vented buffer tank though. House system has heat exchanger though.

If I read the information correctly - the buffer tank will have a float on it which acts as a break in supply. You are correct however if this is not the case, and a double check valve will be required if it is a mains feed - but then you will also require expansion and pressure relief of some form (maybe a vented tap
Combination boilers use heat exchangers to heat your hot water - you just need to ensure you do not get a spilt and get cross contamination.

 

[Dman2]

No
There is no float in the buffer tank, that would make it a header tank
This is a 100kw biomass boiler with a 2500lt buffer tank to store hot water.
What I am wanting to do will be totally separate from the water in the buffer tank.
Probably not a good idea to put a non return in what I am planning because that would create a pressurised system which would vent each time you open the tap.
Would you normally have a non return in a combi boiler on the domestic hot water side?

 

[Ukjay]

No
There is no float in the buffer tank, that would make it a header tank
This is a 100kw biomass boiler with a 2500lt buffer tank to store hot water.
What I am wanting to do will be totally separate from the water in the buffer tank.
Probably not a good idea to put a non return in what I am planning because that would create a pressurised system which would vent each time you open the tap.
Would you normally have a non return in a combi boiler on the domestic hot water side?

Unfortunately if you are going from mains - you will need a check valve on the cold feed and associated safety devices - because if you have an instance that allows water to be sucked back into the mains water pipe cut in a road, lower pressure and your heat exchanger was running with a split and the sealed side contains chemicals and draws back into the mains etc - then you can be prosecuted.

There are many instances where check valves are not installed in the correct places - and even today, there is probably a 50 / 50 split between plumbers on where to fit the check valve when installing a boiler, which makes it difficult for people to know what is right or wrong

Also - the combi boilers sealed sides should be isolated from the mains by removing the filling loop - but most leave them on.

This is why there should be a check valve on the mains feed to the boiler - as when you open the hot tap and you have a split heat exchanger - you could draw into the mains rust inhibitors, additional chemicals that have been used as flushing agents etc.

Below I have added for you a typical picture of an installation for a Combi Boiler - which shows that the check valve must be fitted to the feed, along with an expansion vessel, but sadly not many follow this requirement.

 

[Dman2]

Your obviously not grasping what i am doing.
I am not touching the sealed side of the system or planning to couple mains water up to it.
I am installing a heat exchanger which has 2 parts to it.
1 the side that that the heat is pumped through which will be part of the sealed system
2 the part that cold water will be fed through from the mains which will come out if the other end hot and be fed to the taps.
There will be no connection between the 2 sides other than the transfer of heat from one side to the other