DouginMB,
I glad you have sorted out a portion of the issues. Sometimes the most obvious things are right there in front of us.
I'd encourage you to address the low delta T and capacity issues head on and consider all the options. There are an awful lot of small fixes proposed out there that...
Throw out the 3-way valve. Buy a pressure-independent modulating 2-way control valve. Control with the coil leaving air temperature. Observe high delta T performance with no additional fan energy. You may have to see it to believe it.
Imok2. I'm talking about a single pressure independent modulating 2-way control valve installed on the return side of the hot water coil. No balancing valve required.
Imok2,
Coils only set the delta T at design flow. In all other cases, control valves set the delta T. This coil is clean.
When you read DouginMB's specs for the coil, you will see that its design parameters are 52.2 deg F delta T on the hot water with 160 deg F EWT.
Actual measurements show...
DouginMB,
2 Questions:
1) Is their a larger AHU upstream serving multiple VAV boxes? I am wondering if there is not significant variation in leaving air temperature off the hot water coil.
2) Were the temperatures measured at the same moment in time? Is it possible that the discharge air...
imok2,
I'm surprised to see you recommending additional air flow to raise the delta T. Sure it will work. Throw more air at the coil and the delta T will rise to make up for the poor control valve performance. Pretty typical band-aid for a low delta T issue, and a waste of energy if...
"Should" the key word. Design delta T can be achieved when system differential pressure across the valve is constant and flow is steady, however, in most large hydronics applications, this is seldom the case. You do have a good point about counterflow.
Furthermore, design delta T at...
lilliput1. Absolutely true, the actuator must have sufficient strength to handle the service pressure and leakage at close off pressure must be nil. Many conventional control valves behave more like solenoid valves when insufficiently sized to handle the actual system pressures and pressure...
There is a lot of very good input in the above responses to your original post. I agree in particular with the comments to keep the operation simple (moonpe, imok2). I'm working with a large university campus variable primary flow system. There are a couple of observations we have made that...
As I previously stated, there is a time lag associated with repositioning a control valve when it experiences a change in system pressure.
If a conventional valve with a Cv of 100 has 5 psi drop across it, the flow is 224. How much time does it take a pneumatic or electric actuator to return...
Imok2, Lilliput1. I'm aware of the company you mention but am not planning to use their product. My plan is to use the pressure independent control valve produced by Flow Control Industries (www.flowcontrol.com). Among other material, I have found to be an excellent resource.
You can find...
lilliput1,
Repositioning the valve in response to a pressure change will typically have a significant lag time. Is this what you mean?
Most conventional control valve actuators are designed to fully stroke in well over 1 minute.
With these same actuators on a pressure independent control...
Quark,
All a balancing valve does is clip the flow if it exceeds the maximum set by the balancer. It does nothing to balance the system at part load conditions. This is why delta T in many systems tends to degrade at part load, either at the AHU coils or in the plant.
Pressure independent...
Would one of you in this forum point me to a good resource to study the different options and technologies available for power factor correction. I'm a mechanical engineer that needs to get up to speed starting with the basics.
Is there any consensus on the best approach?
Thanks
