Chiller cooling loop for multiple cosmetics mixing machines - need advice

[HollyBoni]

We make various cosmetics products at our company, and we're looking at getting a chiller to cool our jacketed mixing machines. I already built the "hot" side of the loop for 1 mixing machine with a circulation pump, expansion tank, plate heat exchanger. Now i'm looking at building the chilled water side.

I'll have a chiller, pump, buffer tank. We're planning to have 3 mixing machines that need cooling. Each mixing machine will have it's own heat exchanger, PID controller, and circulation pump on the hot side. The PID controller of the mixing machines controls the heating elements inside the mixing machine, and when cooling is needed, it opens some kind of a valve (I built the first mixing machine with a motorized ball valve).

When a mixing machine needs cooling, the PID opens a valve, which let's chilled water flow through the heat exchanger of the mixing machine. We might cool 3 mixing machines at the same time, or we might only cool one at a time. The chiller might also run without any of the mixing machines calling for cooling. Each mixing machine needs a fixed water flow rate regardless of how many mixing machines are being cooled at the same time.

So my question is, how should I build out this system, what's the common setup for something like this?

My idea so far:
I'll have 1 pump that circulates water between the chiller and the buffer tank, and nothing else. Then a secondary pump that circulates water between the buffer tank and the mixing machines. This is where I kind of get lost.

Should I get one bigger, smart pump that can regulate itself based on stuff like differential pressure, and then just have zone valves that the PIDs open? Or should each zone get it's own smaller pump instead? Should I do a bypass line and branch off of that? Should I get a more powerful, "dumb" centrifugal pump and use things like PICV valves to regulate flow to the mixing machines?

The solution is probably pretty simple and i'm just overthinking it. Any help would be appreciated.

 

[Btutiful]

Like you said, there are a few ways to do it.

If you want to keep the primary-secondary idea where you are using one pump for the chiller and another for your mixers (and you're willing to replace some valves), then you could use 3-way valves at each mixing machine that will bypass the flow when it's not needed or allow the flow through when it is. Two mixers would branch off of a main supply and return line, and the last mixer would be what connects the supply to the return. Use a variable speed motor on the secondary pump and some balancing valves for each mixer and you'd be set as far as I can tell.

Disclaimer: I've only designed one chilled water system and the rest of the systems I've looked at have been conceptual.

 

[Rputvin]

You only need capacity control on one side of each heat exchanger. You don't need flow control or variable speed pumps as long as you use 3-way valves.

If the mixer side has a valve that can control cooling water temperature, then just let the chiller side flow. The chiller will maintain its setpoint temperature, and the buffer tank will absorb thermal mass to prevent the chiller from short-cycling. Chillers like to have stable flow and temperature, they really don't like having flow turned off. Pull from the buffer tank to keep the chiller stable, then through the chiller, and then to the heat exchangers.

Three small mixer loops, one large chiller loop with the 3 heat exchangers in parallel. 4 fixed speed pumps that run full time, and 3 3-way actuated control valves total. You may need balancing/throttling valves depending on how the system arrangement and pump sizing goes on the chiller side.

You can get fancy and add more features, but its more complications and more inter-dependency and more complicated controls.

 

[HollyBoni]

Like you said, there are a few ways to do it.

If you want to keep the primary-secondary idea where you are using one pump for the chiller and another for your mixers (and you're willing to replace some valves), then you could use 3-way valves at each mixing machine that will bypass the flow when it's not needed or allow the flow through when it is. Two mixers would branch off of a main supply and return line, and the last mixer would be what connects the supply to the return. Use a variable speed motor on the secondary pump and some balancing valves for each mixer and you'd be set as far as I can tell.

Disclaimer: I've only designed one chilled water system and the rest of the systems I've looked at have been conceptual.

I'm not sure if i'm understanding this correctly.

So I have a 3 way ball valve that the mixing machine controls. Let's say the first mixing machine in the loop calls for cooling. Does the ball valve divert all flow, and does all the cooling water go through this one 3 way ball valve and HX? If the next machine calls for cooling as well, does all the water flow go through the first HX, then it goes to the next HX? Isn't that problematic?

 

[HollyBoni]

You only need capacity control on one side of each heat exchanger. You don't need flow control or variable speed pumps as long as you use 3-way valves.

If the mixer side has a valve that can control cooling water temperature, then just let the chiller side flow. The chiller will maintain its setpoint temperature, and the buffer tank will absorb thermal mass to prevent the chiller from short-cycling. Chillers like to have stable flow and temperature, they really don't like having flow turned off. Pull from the buffer tank to keep the chiller stable, then through the chiller, and then to the heat exchangers.

Three small mixer loops, one large chiller loop with the 3 heat exchangers in parallel. 4 fixed speed pumps that run full time, and 3 3-way actuated control valves total. You may need balancing/throttling valves depending on how the system arrangement and pump sizing goes on the chiller side.

You can get fancy and add more features, but its more complications and more inter-dependency and more complicated controls.

I'm trying to wrap my head around this but i'm not sure if i'm there yet. Where and how would I connect the heat exchangers exactly?

A few details I might have missed. When we're heating up the mixing tanks, the HX is part of the loop, so I can't have chilled water flowing through it. The heat exchangers are also mounted next to the machines, while the chiller will be in another room.

 

[SAK9]

Stay away from 3 ways valves and such stuff .This is not a HVAC cooling loop. It is a process cooling loop. You need to have a secondary cooling loop that draws water from the buffer tank and returns it back to buffer tank. If the cooling temperature is process critical you may need to use a tank with separate hot and cold wells. Each cooling jacket needs to have a its own own on/off valve.The secondary loop is to be set up with a motorised bypass valve at the end of the pipe that will will maintain the minimum safe pump flow when all jacket valves are closed. The bypass valve may be set to open/modulate/close based on the differential pressure between supply and return pipes which will vary between a minimum and maximum(minimum=all jacket valves open, maximum=all jacket valves closed).If the jacket cooling is required only for a short duration in a day it is wasting energy to keep the pump running all day long.The pump needs to be configured to shut down after a certain time of operation in the fully bypass mode and only needs to come on if one of the jacket valves open indicating a demand for cooling

 

[HollyBoni]

Stay away from 3 ways valves and such stuff .This is not a HVAC cooling loop. It is a process cooling loop. You need to have a secondary cooling loop that draws water from the buffer tank and returns it back to buffer tank. If the cooling temperature is process critical you may need to use a tank with separate hot and cold wells. Each cooling jacket needs to have a its own own on/off valve.The secondary loop is to be set up with a motorised bypass valve at the end of the pipe that will will maintain the minimum safe pump flow when all jacket valves are closed. The bypass valve may be set to open/modulate/close based on the differential pressure between supply and return pipes which will vary between a minimum and maximum(minimum=all jacket valves open, maximum=all jacket valves closed).If the jacket cooling is required only for a short duration in a day it is wasting energy to keep the pump running all day long.The pump needs to be configured to shut down after a certain time of operation in the fully bypass mode and only needs to come on if one of the jacket valves open indicating a demand for cooling

Each machine has it's own PID controller. The PID controller controls both heating and cooling. The jackets have built in heating elements. 95% of the time, we're just cooling hot product to room temp. Some products are filled hot, but this is rare. When a product is filled hot, we set for example 40C on the PID controller. It turns on cooling until the jacket temp reaches 40C, then it keeps it there by fine controlling the heating elements inside the jacket. These are cosmetics products, not pharmaceutical or anything like that, super accurate control down to 0.1C or something is not necessary.

The idea so far:

Primary loop, it just circulates between the chiller and buffer tank.

Secondary loop, this is where the mixing machines get their cooling water.
Each mixing machine will have it's own branch from the secondary loop with a small pump. I need about 30-40lpm through the heat exchangers, so a small circulation pump should do the job. Each branch will have a 3 way L port motorized ball valve, which will be controlled by the mixing machine PID. When there is no cooling needed, the motorized 3 way ball valve will divert flow through a bypass line back to the buffer tank. When cooling is needed, the PID will tell the motorized ball valve to divert flow through the HX.
I could connect the small pumps to a switch on the control board of the mixing machine. I also thought about wiring it to the PID so it would only turn on when cooling is needed, but that might result in short cycling. Even if the pump would run for a short while when cooling is not needed, I don't think it's a big deal, because these small circulation pumps don't consume much power and are designed for continous use.
Since each mixing machine would have a fixed speed water pump, flow distribution shouldn't be an issue regardless of how many machines are being cooled at the same time. At least I think.
Any issues with this layout?

To give you an idea. A cooling cycle with a 150l machine usually takes about 40-45 min currently. After that we turn off the mixing machine completely and get ready for the next batch. On this machine there is also a small water pump on the hot side which circulates water through the jacket and HX, we turn this on and off manually with a button on the control panel.