Help with retrofitting ice rink chiller
I'm brand new to the forum and I'm hoping I can get some help. I've been hired by an Electrical Contractor to redesign a control panel for a chiller system for an ice rink. At first it didn't sound like a big deal but the more I read about chillers I'm realizing there is more to it than meets the eye. The last thing I want to do is destroy some equipment. I've designed many electrical systems in the past (not for chillers or refrigeration equipment) so I don't need help with the electrical end, more with the theory of operation and terminology regarding chillers.
The existing system has three 50Hp compressors but one hasn't worked for several years. They want to eliminate this from the system and only use two compressors. The compressors have a water ciculation pump and each compressor has a water solenoid associated with it. There is a condensor with a 2-speed, 10Hp fan and a 1.5Hp water cooling pump. The system also has a 20Hp Brine pump. There is a set-back timer (stand-alone) and a thermostat.
In this existing system it appears the Brine pump starts (from the setback clock and thermostat) and then compressor #1 starts after a time delay then compressor #2 starts after a time delay and then compressor #3 starts after a time delay. The compressor water pump runs whenever any compressor is running. The condenser fan runs when an RAHP switch activates it and the condenser water pump runs when an RAHP switch activates it.
The RFQ (which isn't very detailed) asks the new system to have a VFD on the Condenser fan. It also asks to use a Honeywell 4-stage rink thermostat with set-back clock.
So here we go, time for me to show my ignorance. Please be gentle with me! What is meant by 4-stage? Is each compressor a stage? So instead of having timers activate the compressors would the 1st stage be to have compressor #1 turn on then if temperature isn't met then 2nd stage (2nd compressor) turns on? If so, then this is really a 2-stage system isn't it? Is the brine pump considered a stage? We've selected a Honeywell T775P controller which can have up to 12 stages. When used as a 4-stage the manual says you can dedicate the last stage as a pump output that would turn on when any stage 1 to 3 is on. Would I use this for the brine pump, or possibly the condensor water pump?
I appreciate any feedback. Thanks.
I'm not trying to sound rude, but if you do not have any experience with chillers or refrigeration systems, you absolutely shouldn't be redesigning a chiller control panel. There are MANY safeties in the control panel that protect the equiptment and life safety. I don't think anyone in this forum are going to advise you on this.
Last edited by R123; 07-25-2011 at 09:33 PM.
Ice rinks are a whole different ballgame! We have a 4 stage stat on one rink that I help out on, and I believe the first stage is the brine circulating pump, then compressors 1,2,and 3. But this uses a sensor embedded in the rink floor to sense ice temperature.
My advice would be to contact an ice rink company to supply you with a control panel to fit your needs. You didn't say what type of compressors you have. I hate to assume , but lets go with recips. Once they stage on, how do they load up? on suction pressure or by a multistage temp controller? Are the units freon? or AMMONIA? You said each compressor has a water solenoid, is that for the water jackets on the heads?
I think you need to gather up a lot more information, as you will need to incorporate safeties, alarms, timers, sequencer, and a few more items into your panel. Your in Canada, contact Cimco, and let them custom design one for you.
Yes, there is a sensor in the floor. They are Cimco compressors and the system uses Ammonia. Alarms are straight forward; no problems there. Again, control panel design isn't an issue, I've done this every day for the past 15 years. Knowing the requirements of a chiller is my problem. Thanks for the info.
Originally Posted by HVACFITTER562
Ok, we now know that we have ammonia compressors, is the evaporator a flooded tube and shell with a level sensor on it? How many liquid feed solenoids, 1 or 2 ( my guess would be 2) Then there should be a high level safety switch in case the level get to high in the evap. There needs to be a level controller, to set the ammonia level in the evap. If this is a cimco system, they usually have 2 or 3 sight glasses to monitor the liquid level on the side of the shell.
Am I close, I think I have almost the same system, cimco put a new panel on this one about 1998. Once we know what equipment you have,its a pretty straight forward sequence of operation.
Thanks for your help. If you read my previous post you'll see I now have a mechanical flow diagram and I'm assuming it is a flooded tube because the tube on the diagram is labeled "ABBCOR Brine Chiller 16" diameter x 12'-0" LG. FLOODED AMMONIA". There is a high level float switch which shuts down all the compressors in the existing system if activated. The only solenoids wired in the system are 1 for each compressor that appear to be water solenoids that control water from a water pit, pumped by the compressor water pump, to each of the compressors. I do not see a level controller anywhere in the system. If you could tell me the what a typical sequence would be that would be great. Thanks.
Originally Posted by HVACFITTER562
I didn't take you as being rude, I appreciate your comments. That's why I'm doing research. If I need to contact a refrigeration company then that's what I'll do. However, that being said, I don't see many safeties in the existing system. Not to say that's how the new system should be. I know in my industry safety devices have changed drastically over the past decade so I'm sure the same can be said for chillers. Thanks.
Originally Posted by R123
Whisper, you will need to be more specifc as to exactly what you plan on retrofitting. You said you're going to "redesign a control panel for a chiller system". Most of the Cimco refrigeration systems tend to use a microprocessor for compressor control and safeties and a relay panel for the remaining equipment. Do you plan to eliminate/replace the microprocessor if one exists? The compressor, although it says Cimco, is more than likely just a Mycom reciprocating compressor with the Cimco name on the heads. If you plan to eliminate the microprocessor then you need to ask yourself even more questions such as: Is it a screw compressor or reciprocating? Does the compressor have unloaders? What type of oil cooling? What type of capacity control? etc. etc. etc.
Where are you reading that it's a 4 stage? A typical ammonia refrigeration system is either single stage or two stage. The brine pump would not be considered a "Stage" as far as refrigeration. After reading your post it sounds like you will be using the Honeywell T775P to control the sequence of events such as turning equipment on or off. Don't confuse sequencing with "stages" in a refrigeration system. If a refrigeration system is two stage it means the discharge of the first stage compressor goes to the suction of the second stage compressor or it's a compound compressor where you have two stages in one compressor (simple version). I just googled that T775P and it looks just like I thought it would. It's something you would find in a grocery store maybe controlling a walk in cooler. If the one I saw is the actual controller then you must be keeping the microprocessors because the T775P doesn't have the capability of performing all the functions an ammonia compressor requires. I'm not a fan of honeywell controls or most microprocessor based controls. Give me an Allen Bradley ControlLogix 5000 PLC with an HMI anyday.
If you can, please clarify exactly what you're retrofitting. That will determine how in depth people need to be when/if they reply.
Thanks for the reply, I do appreciate the input. I wish it was an Allen-Bradley system! I spend 90% of my time programming ControlLogix, CompactLogix, PanelViewPlus, FTViewME/SE. That is more up my alley. Anyway, it is not a micro-processor based system and they do not want a micro-processor based system. Its a hard-wired control system with failing components that they basically want replaced with new and with some modifications. For example they want a soft start on the brine pump instead of across the line. They want a VFD on the condenser fan motor instead of a 2-speed motor. They want (yes they specified) a Honeywell 4-stage controller to replace their existing Ranco 2-stage controller and seperate Intermatic setback timer. Perhaps "re-design" was too strong a word. It's more like a replacement of components with a new electrical drawing, wire numbers, and some changes to components. I just want to be able to understand the system and not blindly replace components.
Originally Posted by Just Some Guy
I just came across a mechanical diagram which shows additional information. This is what is on it:
- CIMCO Model CEHOH Evaporative Condenser - capacity 56 tons
- ABBCOR 1008 Surge Drum
- ABBCOR Brine Chiller - Flooded Ammonia
- Howe reciprocating compressor Model 2 CYL Capacity 25TR, 40HP
- YORK? reciprocating compressor - the drawing is very faded I think it says York but the first letter is really hard to read - Capacity 31TR
- Condensor water pump - 1.5Hp
- Compressor water pump - 1/2Hp
- Each compressor has a Temperature Alarm High, Temperature Indicator, Flow Switch, Pressure Alarm Low, Pressure Alarm High, Oil Pressure Alarm Low, Solenoid Valve (water comes from the compressor water pump). There is also an oil seperator for each compressor with a float valve.
To address some of your other comments. The 4-stage came out of the RFQ for the project where they asked for a 4-stage Honeywell Rink Thermostat with Setback. I recently questioned the customer about the 4-stages and they said "The four stages refers to operating temps and setback temps. In all stages the brine pump is activated first, then comp #1, then comp #2". So I am definitely missing a concept here. I still don't know what a stage is? And you're right, I think I'm confusing it with sequencing. All I have control over is turning the brine pump, water pumps and compressors on or off. So if I have to turn the brine pump on and then comp #1, then comp #2 for "all stages", then what is a stage? I've got nothing else to do, everything is on? What differentiates stage 1, from stage 2, etc. What am I missing? In the mechanical flow diagram the discharge from each compressor goes to a common discharge line (parallel connection) and then to the brine chiller. I don't see anywhere where the discharge of 1 compressor goes to the suction of another.
In the existing system they have a 2-stage Ranco controller but they have the stage 1 relay connected in series to the stage 2 relay which energizes the brine pump and then three timers. As the 1st timer elapses the first compressor turns on and after the 2nd timer elapses the 2nd compressor turns on and after the 3rd timer elapses the 3rd compressor turns on (well not any more, they don't use the 3rd compressor and want it eliminate from the system). This seems like 1 stage to me. The 2-stage controller is acting like an on/off controller. I would have expected compressor 1 to be connected to stage 1 relay, compressor 2 to stage 2 relay, is this wrong?
Thanks again. I'm meeting on-site on Tuesday so hopefully I can get more details and/or things cleared up but if you have any suggestions or opinions in the mean time I would appreciate hearing them.