Minimum discharge pressure for ammonia systems

[Bradford]

Frequency of defrosting is another important factor of refrigeration plant optimization. Right now, here in Ontario, one cold storage has defrosting once per week, but another one has defrosting twice per day. I found that overdefrosting is common problem for many refrigeration plants. It is difficult to justify additional compressor installation, if you have defrosting once per week.

I’ve been reading this post with great interest. What started out as a discussion on lowering head pressure and it’s implications has become a discussion on total system optimization! And it seems to be a topic that a lot of people are interested in. With the ever rising costs of energy and the push for a greener planet, I wonder if this would make a good topic for a forum or sub-forum.

What Sergei mentions about defrosts going from twice per day to once per week has become quite typical in plants that incorporate smarter controls and/or keener operators. Evaporators that require 2 defrosts per day during that one hot week in august can often get away with one or two defrosts during the winter months. This gets back to the problem of fixed setpoints often being the “worst case” setpoint. If two or three defrosts are needed in the summer, that’s where the pins are left in the time clock. If -25 suction kept the rooms cold in August, that’s where the suction is left all year. If one evaporator requires 145# for defrost, that’s where the pressure switches are set. It’s obvious that a lot of systems have a lot of room for energy usage improvements

Another great up-side to long durations between defrosts is you can float the head pressure lower for a longer period of time thus enhancing energy savings.

Brad

[US Iceman]

a discussion on total system optimization! ... I wonder if this would make a good topic for a forum or sub-forum.

That's good idea. Let me run it past the boss of RE for his comments.

[US Iceman]

It’s obvious that a lot of systems have a lot of room for energy usage improvements

That was my idea for starting this thread. Refrigeration systems waste too much energy doing something that can be done for less.

I continue to believe the system can be designed better and more flexible. The control systems actually provide the ability to sustain the original design concepts with the capability of smarter operation.

One other important criteria is the utility bills, i.e., how much energy and demand cost, the various time of use charges, and ratchet clauses can also present some challenges.

[stan1488]

recip plant on vfd ( im giving my tricks away) :P

[TXiceman]

recip plant on vfd ( im giving my tricks away) :P

This is nothing new, I did this years ago and it worked like a champ on lowering energy demand and smoothing out plant operation.

You have to think outside the box all of the time now.

Ken