Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Search results for query: *

  1. Rhonda2

    Variable flow chilled water system - Question?

    Looks like a lot of extra pumps. Why not consider variable primary flow instead?
  2. Rhonda2

    Bizarre VAV problem

    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...
  3. Rhonda2

    Bizarre VAV problem

    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.
  4. Rhonda2

    Bizarre VAV problem

    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.
  5. Rhonda2

    Bizarre VAV problem

    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...
  6. Rhonda2

    Bizarre VAV problem

    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...
  7. Rhonda2

    Bizarre VAV problem

    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...
  8. Rhonda2

    AHU LAT Variation 48-56 deg F

    "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...
  9. Rhonda2

    AHU LAT Variation 48-56 deg F

    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...
  10. Rhonda2

    Variable Primary Flow CHW and CHW temperature reset

    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...
  11. Rhonda2

    AHU LAT Variation 48-56 deg F

    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...
  12. Rhonda2

    AHU LAT Variation 48-56 deg F

    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...
  13. Rhonda2

    AHU LAT Variation 48-56 deg F

    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...
  14. Rhonda2

    AHU LAT Variation 48-56 deg F

    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...
  15. Rhonda2

    power factor capacitors

    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
  16. Rhonda2

    variable volume AHU

    Herman2. Do you know the supply and return water temperature performance across the cooling coils on a typical cooling day? What is the leaving air temperature setpoint? Is it stable and consistently achieved in operation? I typically like to explore these issues before considering VAV...
  17. Rhonda2

    AHU LAT Variation 48-56 deg F

    With pumps turning on and off and changing speed while control valves are opening and closing, I'd contend that it is unusual to find fairly constant pressure drop across control valves. Small changes in the pressure across a 5 psid valve produces wide swings in the flow. Also, 50% of the flow...
  18. Rhonda2

    AHU LAT Variation 48-56 deg F

    Seems that many have focused on the control valves close to the central plant. Wilg brings up a good point about the valves at the end of the line. In many systems, it appears to me that excess flow further down the line leads to an increases the differential pressure across valves closer to...
  19. Rhonda2

    AHU LAT Variation 48-56 deg F

    With conventional (pressure dependent) control valves installed at large cooling coils, what leaving air temperature (LAT) variation should be expected relative to setpoint in operation with modern controls? Does it vary depending on the location of the coil in the system? We are seeing...
  20. Rhonda2

    Pressure Independent Characterized Control Valve.

    Pressure independent modulating control valves have been in the market for a while and are emerging in more and more applications. In addition to the PICCV and Optimizer, it is worth checking out the DeltaPValve. Type it into any online search engine.

Part and Inventory Search

Back
Top