3 Port valves have been fitted on most systems installed in recent years but the third port has been blanked off or incorrectly connected on most installations.
The third port has been used on some installations to bypass fluid between headers which is not good engineering practice.
This article applies to both heating and cooling valves.
Mushroom heating installations are not as important as cooling but on poultry installations with finned pipes for heating 3 port valves are essential for correct operation.
The practice of using high capacity circulation pumps with water chillers has worked OK but problems can arise when extra units are added with different coil designs and sizes.
The pumps require high energy input and on the better installations this has been partly addressed by the use of constant pressure pumps.
In my opinion each coil should have its own pump which can be controlled by pressure or from same modulating signal as valve. The header pipe only needs a relatively low pressure: say 0.5 bar compared to 1.5 bar normally used.
Please see diagram.
The direction of flow and position of pump and valve is for illustration purposes only.
If we use 3 port valves correctly and connect the coils in counter flow then we will maximise efficiency and capacities.