Variable Flow on Both Sides of a Plate Heat Exchanger
Variable Flow on Both Sides of a Plate Heat Exchanger
(OP)
To provide separation between existing Landlord and Tenant in a Commercial Office HVAC heating and cooling pipework circuits, I am considering the introduction of plate heat exchangers.
The fluid on both sides will be water, with standard water treatment, and operating with an approach of 2K. The secondary circuits are variable volume flow, and the existing fan coil units are two port control; therefore, the tertiary pumps will also need to be variable volume flow to avoid stripping out large numbers of valves and re-commissioning.
So far I have been unable to locate guidance on a suitable control strategy, and would be interested to hear horror stories of similar installations that could not maintain control, OR that a simple PI loop will provide adequate control.
The fluid on both sides will be water, with standard water treatment, and operating with an approach of 2K. The secondary circuits are variable volume flow, and the existing fan coil units are two port control; therefore, the tertiary pumps will also need to be variable volume flow to avoid stripping out large numbers of valves and re-commissioning.
So far I have been unable to locate guidance on a suitable control strategy, and would be interested to hear horror stories of similar installations that could not maintain control, OR that a simple PI loop will provide adequate control.





RE: Variable Flow on Both Sides of a Plate Heat Exchanger
knowledge is power
RE: Variable Flow on Both Sides of a Plate Heat Exchanger
Thank you for your comment.
Both sides of the PHX are closed circuits and will have a strainers in front of the circulator and PHX; which should reduce the risk of fouling. In addition, a valve exercise routine will be run once a week, which should help reduce any build up on the plates.
RE: Variable Flow on Both Sides of a Plate Heat Exchanger
as regards to operating conditions, few times i had some very unusual temperature regimes, and manufacturer's specialists convinced me that exchanger itself will not have trouble with that.
plate exchangers originate from process industry where demands are usually more complex so they are expected to be very robust.
RE: Variable Flow on Both Sides of a Plate Heat Exchanger
rmw
RE: Variable Flow on Both Sides of a Plate Heat Exchanger
Use a pressure transmitter on the fan coil side to maintain flow, and a temperature sensor on the outlet side of the heat exchanger on the fan coil side. Use the temperature sensor to vary the flow on the other side of the exchanger to maintain a set leaving water temperature of the heat exchanger. A temperature sensor on the heating side of the exchanger will be needed to control the heat. A high turndown ratio will be needed on the boiler.
This is just a quick thought, but will hopefully work for you.
PS: an auto-flow regulator will be needed on the boiler(?) side of the exchanger, because as the flow through the exchanger drops, so will the pressure loss.