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microHydro
29-10-2012, 06:07 AM
For a heatpump project, I need to control the flow rate of hot water through a tube in tube desuperheater. Depending on the operating conditions, I need to regulate the hot water flow from 0.16 GPM to 1.5 GPM to heat it to 120F. What are good ways to do this?

mad fridgie
29-10-2012, 07:20 AM
A temp driven regulator valve, can be a mechanical device or electro-mechanical device.

desA
29-10-2012, 07:50 AM
Would temp lags not perhaps come into play, here - especially with low flows?

Gary
29-10-2012, 05:49 PM
You might want to set up a face/bypass circuit where some of the water flows through a bypass, thus reducing the amount flowing through the heat exchanger.

chemi-cool
29-10-2012, 06:05 PM
You might find here what you are looking for
http://www.watts.com/pages/learnAbout/temperingValves.asp?catId=64

microHydro
29-10-2012, 09:36 PM
Thanks, chemi-cool. 131F to eliminate Legionella Bacteria. There is not much penalty for this higher temperature because of the desuperheater counterflow design.

Could someone suggest a specific regulator valve, perhaps with a face/bypass circuit for my application?

Tesla
29-10-2012, 11:44 PM
http://www.solarnetix.com/solar-heating-specialties/zone-valves/160-belimo-zone-valves would be a start then you need a controller for it. It will need P I & possibly a little D control. A three way valve will divert some of the flow for by-pass of de-superheater.

microHydro
30-10-2012, 01:20 AM
Hi Tesla,

It looks like the "3-Way Diverting Zone Valves from Belimo" is on/off only. How could I use it to regulate temperature with flow rate control?

MikeHolm
30-10-2012, 01:26 AM
http://www.solarnetix.com/solar-heating-specialties/zone-valves/160-belimo-zone-valves would be a start then you need a controller for it. It will need P I & possibly a little D control. A three way valve will divert some of the flow for by-pass of de-superheater.

That used to be my old company......long gone (Solarnetix, not Belimo).

MikeHolm
30-10-2012, 01:39 AM
Hi Tesla,

It looks like the "3-Way Diverting Zone Valves from Belimo" is on/off only. How could I use it to regulate temperature with flow rate control?

Nope, Belimo has modulation valves, look for 0-10vdc input. The valves and motor are separate. Danfoss also has a nice flow meter that can be inputted to a control to vary the valve based on flow and/or temp.

Also:

http://www.paw.eu/en/products/solar-thermal-engineering/frischwasserstation.php

It isn't exactly what you want but the idea behind it is to vary the speed of a pump based on the tank temp on the other side of a HX. This gives you stead state DHW from a dead water tank, and the parts inside this thing, and the controller, can do what you want. It may take a bit of experimentation tho....

Tesla
30-10-2012, 04:56 AM
Sorry I just said it would be a start and Belimo has the valves and actuators to do it (from a quick google) - as stated correctly above (thanks Mike) 0 - 10vdc is the best option. That's where the PID control would come in for modulation. I was also thinking more like 1/2" or smaller depending on the application.

mad fridgie
30-10-2012, 05:25 AM
Maybe best to do a little sketch of what you intend for the application and what size is the refrig unit (heat pump)
The application may determine that energy recovery is better than straight out temp recovery.

microHydro
30-10-2012, 05:48 AM
I'd love some design wisdom! Here's the condenser and desuperheater section of the PID showing operating conditions for November. Refrigerant lines are black. The inlet red desuperheater water line is piped from the cold water inlet of a hot water tank. The red desuperheater outlet returns to the outlet of the hot water tank.
9715

mad fridgie
30-10-2012, 06:34 AM
If your draw, from the bottom and introduce back into the bottom via a sparge pipe and have a higher flow rate fixed, you will absorb more energy,
But if you have enough hot water without an element, then the one pass method is OK.
So what you could do on the cheap, is have a simple solenoid valve controlled by the outlet water temp, wait a bit more, there is a minimum flow device around solenoid valve that allows for the flow temp to be measured. I use 0.1L/M for this device (a long capillary tube works well)

microHydro
30-10-2012, 06:54 AM
Thanks, Mad Fridgie
The idea is that I will draw unheated water from the bottom of the hot water tank with a pump, and return the optimally heated water to the top of the hot water tank. An electric element may or may not be active.

Please help me understand the operation of the solenoid valve topology. When the outlet temperature is low, the solenoid at the outlet closes. The capillary tube still flows hot water around the solenoid. When it is up to temperature, the solenoid opens. Have I got it?

mad fridgie
30-10-2012, 07:45 AM
In reverse,
The sol valve control is correct (i have presumed that the water pump is off when the heat pump is off)

The term optimally heated, can either be greatest amount of energy or required temp.