Glycol Recirculation Pump questions

[Josh@HiddenSpgs]

So we have been open for almost two years and had setup our glycol loop the following way:

We have a 220 gallon reservoir which runs through a pump through our loop and returns through our chiller and than back into the reservoir.

We had a service done on our chiller and it was suggested that we add a second pump and make two separate loops. One pump running the actual glycol loop without running through the chiller.

The second loop pumping just from the chiller to the reservoir.

We changed this up and added a second pump that is a 1/8th horse pump rated at 40 GPM (taking into consideration the 6 foot climb to the chiller). It pumps through the chiller and back into the reservoir but the flow coming back into the reservoir is way less than it is rated I am assuming due to running though the chiller and how ever it is setup to chill the liquid is slowing it down.

My question is this:

We were told that it would make the chiller run less and be more efficient. The tank is most definitely running colder, how ever the chiller does not seem to be running less. Can some one explain if I am being paranoid or should I be seeing a huge difference in efficiency? Both of the chiller run cycles and of the chilling capabilities of the glycol system?

My fear is the pump is not big enough to run fast enough through the chiller and is going to burn up the chiller. But logically I would assume if it wasnt getting the flow needed (which the manufacturer said the minimum flow rate is 15 gpm) it would shut itself down and through an error message or something.

Thanks in advance!

Josh

[jebzter]

You forgot to factor in how much head pressure is taken away from pushing glycol through the heat exchanger. You should be able to find out what kind of hx it is and get the specs. There is always a pressure drop across them. Our setup uses a 3/4hp pump for the hx and a 1hp pump for the loop, it works well for us. I am not sure that it will make you more efficient having two pumps unless your loop pump turns off when no cooling is needed. Having dual pumps is a nice redundancy.

[gitchegumee]

A few things....

First, your centrifugal pump will not put out the full volume of liquid unless it's just pouring out the end of the pump. As soon as you put any back pressure on it, the flow slows. This is the starting point of diagramming a pump curve--flow vs. pressure. The arrangement your refrigeration expert suggested is, IMHO, wrong. Any energy you put into your system manifests itself as heat. You pay for this energy. Then you pay again to remove this heat energy. Now you have two pumps adding energy to your glycol. Only really need one for a small chiller. You've already got one pump moving glycol; why wouldn't you use it to chill as well as recirculate?

As for making the chiller run less: no. How could that be? You are adding energy, so it would likely run more often. And because the original configuration had the return of the glycol loop (the warmest part) pumped through the heat exchanger, the temperature differential between glycol and refrigerant is higher and will lead to increased efficiency. As you have it now, the second pump runs continuously even though the glycol may be at your desired setpoint. I'll defer to true refrigeration experts to tell me otherwise, but for a small chiller I prefer one small, low-head pump. I wouldn't worry about the second pump not achieving 40gpm. And I would definitely not expect to see any appreciable efficiency difference. Otherwise, all chillers would be made that way. Good luck!

[Josh@HiddenSpgs]

Thanks for the input guys. I am going to ponder on this and rethink my approach.

Josh