FCU Control Valve

You were doing correctly when by default, you install a series control valve in the "leaving water" side of the coil, but really for a reason that seldom surfaces. You said "keeping the coil full". Well the coil is always "full", BUT, pinching off flow on the downstream side insures higher system pressure within the coil and in certain circumstances, traveling bubbles could expand and "hide" in a coil's "weak circuit" and cause one of the parallel passes to stop flowing. The higher the system pressure, the smaller the bubbles STAY. Otherwise, there's no other advantage for mounting the control valve one side or the other. If someone else points out a btu capacity reduction for mounting the valve downstream versus upstream, I believe this performance loss if any is neglible and doesn't compare to the benefits of keeping traveling bubbles as small as possible.

As for balancing valves, designers often throw them in when they're not really needed AND, they add considerable circuit length ( resistance) themselves, as well as cost. But they have a valuable place in hydronics. Even though a reverse return MAIN LOOP is utilized, "self balancing" only happens if all of the coils or heat distribution circuits are truly equal in effective circuit length....the longest circuit could starve for flow.

After that, the design is pretty straight-forward. Determine the circuit with the highest resistance or head to over come, then add up all the GPM's needed when everyone's calling and last...select your pump to deliver the total GPM required, AT the head needed for the worst circuit and select the pump where this point is in it's optimum operating range....approx. 80% of full head.

Some designers get into trouble when they under-estimate the pumping "penalties" for glycols. Cold glycol water spells trouble, even seperating bubbles is more difficult. Many air purgers will leak with cold glycol. Design with caution.

Thanks Sniccus. Now I feel more confident that relocating the control valve downstream will not affect so much coil performance. As to the issue of air bubbles, you are right that some air may be trapped that's why I have also included an automatic air vent in the piping connection detail. As the renovation project will be in phases, I have opted to include a balancing valve now to ensure that I could measure water flow and set this to required unit's flow. As there are several risers, I intend to add some circuit setters that I may have flow distribution efficiencies maximized. The pumps will be replaced, and I will take note of the increased pressures and select the pumps more accurately.

I'm not a real big fan of air vents, they're seldom installed where they are as effective as one might think, PLUS, they get to leaking over time and making a mess and if they're "outa sight, they're outa mind."

If an airvent is by luck installed at a high point in a hydronic circuit, it still doesn't collect any bubbles until the flow stops, they fly right on by.

I prefer a design that allows me to purge a circuit and see with my 2 eyes, a clean stream of purge water or else pumping glycol into a trash can and waiting for no bubbles to surface.

I DO like the new SPIRO-VENT air seperators. When I've retro-fitted them into systems with troublesome vaporlock areas, these puppies cleaned out the air. Trust me, the extra expense for them is recouped at start-up !

Oversizing air ducts can "kill" a system. Oversizing hydronic mains only adds to installed cost but it then allows a smaller circulator to sufficiently move btu's around.

Undersizing is bad for everyone. If the mains are too small, a higher head pump can help, but then the high velocities of water cause a great deal of new problems. Water hammer, whirring noises in pipes, zone valves don't seal or else they bang when they close, etc.

2 - 3 feet per second is a nice velocity to make sure bubbles get rushed along and don't congregate anywhere. More than that is a waste of pumping HP for heating-cooling applications, unless we're talking specialty designs.

If I have a choice, I always design with primary-secondary-teritary loops using multiple circulators rather than a big pump and zone valves. First cost is close on either design however, a good quality zone valve will outlive a circulator. Problem is, it's harder to design a system with 1 pump and multiple zone valves. I always like chasing water thru a boiler. This maximizes the burner duty cycles and minimizes potential for thermal shock and it ensures that all the btu's it can produce will be swept out of the boiler. ( Primary loop design.)

The nice thing about multiple circulators and injection pumping etc. is that system flows are not usually a problem and most troubleshooting can be done by "feel".

Another neat little trick I do is go to Radio-Shack or other electronics supplier and get those "el-cheapo" neon indicator lights with the short leads. I pop them into the spare knock-out plug on the circulator's electrical junction box and slip the wires right in with the power feed, then there's instant recognition if a circ has power. If the circ has power ( light is lit ), and the lines are cold, the pump is locked up, if the pump has power and the circuit is cold but the lines are hot near the pump, then the circuit is vapor locked, if the lines are hot and the circuit is overheating and the circ light is out, then the flow control valve is leaking thru, and if the circuit's cold and the light is out, that's obvious, we check the relay but we don't need to remove inspection caps on pumps or stick our ear against a potentially hot circ body to see if its running...what a time saver !

Considering that the present retrofit project is for systems already more than 20 years old and have never been before refurbished in their entirety except for some equipment replacement, we have so much work to do. I shall take note of your suggestions and adapt them to where these will be applicable. Thanks for these, Sniccus. I really appreciate them

Hydronics are fun until they don't work ......