Temperature Control Unit... Glycol heating and coolgin

[WilliamTz]

Hello Engineers,

I have a small glycol system at -5degC in a primary/secondary pumping arrangement.

The glycol serves process vessel jackets through a Temperature control unit, to cool and heat the process inside of them...see attached sketch....each approx 15kW.
The glycol control valve at the secondary side controls the set point temperature when cooling is required.
Sometimes the jackets needs heat (80degC) so a steam heat exchanger on the glycol line before the jackets heats the glycol. During this time the control valve serving the secondary side is closed off and the secondary circuit just circulates around its own loop.

My question is; is there any fear that the heat from the secondary loop could get back up and into the primary loop though convection or conduction.?..
Is there any way of preventing this?

Note I have an allowance in my system for expansion and for the slug of heat back to the chiller for when the system goes from heating to cooling (with a buffer tank)

Will

 

[LittleInch]

As the glycol heats up inside the loop it will therefore expand and push back into the primary circuit, but the volume should be small and if your branch line is long enough it won't mix.

There will always be a little bit of intermingling when you don't have a valve to prevent it, but this should be relatively minor so long as the tee off the main primary circuit isn't too short.

Is there a valve missing on your short header? otherwise this is a short circuit when operating in cooling mode no?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[WilliamTz]

LettleInch
In cooling mode chilled glycol is delivered to the short header and the valve on the return line opens to meet the SP temp requirements. The secondary pumps take the water form the header and delivers it back into the header again on the return line. I always believed valves or non return valves on the decoupling header is a big no-no.

 

[LittleInch]

OK, I'm no expert in these, but it doesn't look right to me.

This looks like a flow and return system so the primary flow is out through on e header pipe and back trough the other. If there is no VFD, then the flow header will need to be a higher pressure. But with your design you are equalising pressure between the two headers at all these nodes which doesn't look good to me. If we assume no elevation difference, pressure in the flow header at point 1 of your system needs to be higher than the end point otherwise you get no flow. Ditto, the return header pressure needs to be higher at the end point than the first point otherwise there is no flow.

It just doesn't look right to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Agreed, dont see how the heat cycle would work if that secondary loop bypass line were to be left open - there ought to be an auto valve that closes in heat mode.
Also, there ought to be a check valve on the primary feeder to secondary loop to prevent reverse flow of hot glycol back into main primary header in heating mode (and then into some other secondary loop).
Presume the expansion drum is some where on main return header.

 

[Heaviside1925]

I think I can see how this system works.... but if you can add to the two states, cooling mode and heating mode and provide their flow paths, I think it might help to understand the system. To just control flow direction, there are plenty of options but to recommend anything, I would prefer having a full grasp of the system. At first glance, I wonder if moving the valve from the glycol return side to the supply side might be appropriate.

Also, thank you for removing your duplicate posts.

 

[georgeverghese]

Must say this is a rather sloppy diagram. There are probably many details not shown or described.