Help With Injection Moulding Cooling

[Refrigerologist]

I have a client who currently chills their thermoplastic injection mould machines via a chilled water system that consists of an indirect loop system. This has two water tanks. The first (the hot tank) receives the heated water back from the mould heads and is piped via a balance pipe to the cold tank. The cold tank water is pumped to the mould heads. These tanks have their own pump set operating in a loop.

The chillers are piped into the tanks with the flow being to the cold tank and the return from the hot tanks. This circuit also has its' own loop pump set. These tanks are open vented with a top up tank above.

The client would like to have a closed loop system. I have suggested that this can be done using a chilled loop system complete with its' own pump set and a buffer vessel. The mould head loop would be connected directly into the chiller loop with its' own pump set. I thought this would be OK, but now I am concerned that the water return temperature from the mould heads may be too high for satisfactory control.

Any one have any experience of injection moulding close loop or is this a no no without a intermediate heat exchanger?

[chemi-cool]

I have done a few plastic factories,
PM me your email and I will send you the best and cheapest way to cool water for plastic injection.

Like your tools........;)

[icecube51]

in my opinion are the water tanks not big enough tho stand up to the moulding machines. i think its better to recalculate the installation,maybe whit the idea of thermal storage.

Ice

[icecube51]

Hey Chemi, i have interest to.

thnx,

Ice

[US Iceman]

...maybe with the idea of thermal storage.


Good idea! This depends on the time-of-use, demand for cooling, and variation in the cooling loads also. Thermal storage is an excellent way to reduce the On-Peak demands if the situation will allow it.

Although... What I think Refrigerologist is looking for is a way to make the system closed loop, which is probably due to contamination of the water and the chiller. That has been my experience with injection moulding facilities.

If you put it in as a closed loop you will need expansion tanks and air separators. And... this might be a good time to look at variable speed pumping too.

[Refrigerologist]

Good idea! This depends on the time-of-use, demand for cooling, and variation in the cooling loads also. Thermal storage is an excellent way to reduce the On-Peak demands if the situation will allow it.

Although... What I think Refrigerologist is looking for is a way to make the system closed loop, which is probably due to contamination of the water and the chiller. That has been my experience with injection moulding facilities.

If you put it in as a closed loop you will need expansion tanks and air separators. And... this might be a good time to look at variable speed pumping too.

Nail on head! Contamination is the problem. I have allowed for expansion vessels in the circuit and air eliminators. Thernmal storage is not really an option due to space limitations. Also the plant operates 24/7/360 or more days per year.

My only concern is the temperature of the water entering the chiller. I have allowed 8litres of water content per kW of cooling, sorry US imperialists but even I have had to change:D. Anyway it is recommended 6 to 10litres per KW for process cooling. So I should be safe.

Has anyone any experience with closed loop systems on this type of plant?

[US Iceman]

You need to ask the facility people what temperature they want on the supply water, and, what temperature rise they can live with on the return temperatures.

They may even be able to tell you the maximum flow rate (on average) per mould size/shape. You need the temperature differences to help establish the maximum cooling loads for the maximum flow rates. Then you can size the chiller(s).

Most of these facilities use temperatures higher than normal comfort cooling applications so you wan to be sure to have the chiller rated for the actual operating conditions, NOT those for air conditioning.

I might also suggest the installation of a permanent strainer in the water lines to the chiller. You don't want to plug it up with old debris found in the existing system.

[Refrigerologist]

You need to ask the facility people what temperature they want on the supply water, and, what temperature rise they can live with on the return temperatures.

They may even be able to tell you the maximum flow rate (on average) per mould size/shape. You need the temperature differences to help establish the maximum cooling loads for the maximum flow rates. Then you can size the chiller(s).

Most of these facilities use temperatures higher than normal comfort cooling applications so you wan to be sure to have the chiller rated for the actual operating conditions, NOT those for air conditioning.

I might also suggest the installation of a permanent strainer in the water lines to the chiller. You don't want to plug it up with old debris found in the existing system.

The chiller load size is not a problem. The client has 2 20kW chillers rated @ 9 deg flow temperature. He wishes to upgrade and he would like 2No. 40kW (ish) machines as replacements. These will be run and standby. Existing pipe sizes will not be a problem as they were oversized when installed to allow for increase in production.

I have selected 2 Daikin machines that have a capacity of 37kW at 7 deg C so nearer to 40kW at 9 deg C. My only concern was the returning water temperature from the mould heads. If this is higher than 14 deg C, then with a delta T across the chiller of around 5K we may not meet the target temperature he requires of 9 deg C flow temp even with a buffer vessel installed.

I had anticipated installing a sealed loop system consiting of ABS plastic pipe with a buffer vessel and air eliminators installed. An auto top up/pressurization unit would also be installed. Strainers before each chiller have been allowed for, and each chiller is equipped with its own expansion vessel and water pump.

Why has it been standard practice to install open vented systems, with a hot and cold tank? Are closed systems inadvisable for injection moulding process cooling?

[US Iceman]

Why has it been standard practice to install open vented systems, with a hot and cold tank?


My guess is: this has been the way it has always been done. Most of them I have seen either have a tank or no tank at all and all were open loop.



Are closed systems inadvisable for injection moulding process cooling?


No reason I can think of.

As far as capacity required and temperatures go; make sure you have everything in writing from the customer as to the required temp's, etc. If you provide what he asks for, then it's his problem. If you make an error, guess who gets it then?

[Refrigerologist]

Iceman, thanks for your comments.

I have checked at the factory and the system is pretty useless at present. The chillers are delivering water at 5 deg C to the cold tank, but the cold tank is actually at about 14 deg C, this is because it has 2 balancing lines directly connected to the hot tank. The hot tank (return tank) is receiving water back at about 16 to 17 deg C. So the delta t is only 3K across the mould heads. I am pretty sure that a closed loop system will work far better than this; if we can deliver water at 9 Deg C, and it only lifts 3K, we are not going to see a problem.

I think I will tee into the existing system and fit isolation valves so that we have a closed loop with the tanks isolated. Then I can prove our equipment works correctly before removing the old kit, or the tanks. At least that way we can keep the factory operating if we need to alter design slighty. A bit belt and braces but far better than paying lawyers!

[multisync]

Can you not 'free cool' the hot tank with a large radiator and fan assembly outside. For a large part of the year ambient remains below 10c which will take the top off.

Not a total solution but an energy saving addition for sure.

Multisync
London

[Refrigerologist]

Can you not 'free cool' the hot tank with a large radiator and fan assembly outside. For a large part of the year ambient remains below 10c which will take the top off.

Not a total solution but an energy saving addition for sure.

Multisync
London

I had thought about installing a free cooler, but at the end of the day the client has limited funds and in the past they have bought in a company from Lithuania to carry out work for them, (we can't compete with those labour rates). So I dont want to get to complicated at this stage. A free cooler can easily be added at a later date.

I am just trying to get rid of an open vented system that gets contaminated with algae etc, and causes problems to both the injection heads, and the chillers.

[The Viking]

So the main issue at the moment is the water migrating from the "hot" tank in to the "cold" tank.
The only reason for this would be imbalance between the waterflow in the loops.
In your case you must have more water flowing on the factory side than on the chiller side.
THIS WOULD REMAIN THE SAME IF A CLOSED LOOP WERE INSTALLED.

Normally this happens when the customer has added more machinery (together with a new pump) on the factory side or when the chillers' strainers are partially blocked.

Back in the good old days when I got my hands dirty, I were involved with the cooling of quite a few plastic factories... We always tried to balance the waterflows so that little or no migration happened, if there were a difference we tried to ensure that the chiller side had the highest flow (=cold water migrating to the hot tank).

Back in those days the reason for open tanks with automatic float-fill-valves were that they always kept having leaks out in the factory or in their machines and the tank systems coped better with high loss situations.

[chemi-cool]

The connection between the too tanks is only for levelling the the water quantities.

Hardly any heat is transfered to the cold tank.

My scanner is dead so I can not up load a schema of the water lines.

it is much better to have the water tanks at ambient pressure and not having a closed loop, it creates problems with returning water.

A mixing valve is the secret of energy saving and keeping the cold tank at 10°C while the hot tank is at 22°C.

I have built this system 20 years ago and while the number of injection machines grew 50%, only one 25TR chiller was added and the system runs on 80% even on the hottest days [43°C]

[icecube51]

just thinking out loud here,

is it not possible to have an extra water vessel of lets say 2000ltr where the hot water returns to,make an evaporator like they use in beer-coolers,whit a small compressor unit,lets think 3,5 Kw ,use the same idea of beer-cooling, and then pump the pre-cooled medium to the return vessel before the chiller units,they are in cascade i presume,and then pump the medium or water over the chiller units.i think you can gain 4C° or 5C°, ......i think....:confused:

just an idea,

Ice

[US Iceman]

Depending on how the balancing lines work in the tank they could cause some issues. If there is significant mixing between the hot and cold wells of the tank this can change the actual inlet water supply to the chiller. If this temperature decreases for a fixed flow rate the capacity of the chiller goes down.

Same flow rate X lower TD = lower capacity

[icecube51]

Depending on how the balancing lines work in the tank they could cause some issues. If there is significant mixing between the hot and cold wells of the tank this can change the actual inlet water supply to the chiller. If this temperature decreases for a fixed flow rate the capacity of the chiller goes down.

Same flow rate X lower TD = lower capacity

agree US Iceman,
but i was refering to put this cind of system between the hot return line only, as close as possible to the heat source, don't change the rest, just add an extra vessel whit cooling system.a cind of pre-buffer.:confused:

Ice

[Refrigerologist]

So the main issue at the moment is the water migrating from the "hot" tank in to the "cold" tank.
The only reason for this would be imbalance between the waterflow in the loops.
In your case you must have more water flowing on the factory side than on the chiller side.
THIS WOULD REMAIN THE SAME IF A CLOSED LOOP WERE INSTALLED.

Normally this happens when the customer has added more machinery (together with a new pump) on the factory side or when the chillers' strainers are partially blocked.

Back in the good old days when I got my hands dirty, I were involved with the cooling of quite a few plastic factories... We always tried to balance the waterflows so that little or no migration happened, if there were a difference we tried to ensure that the chiller side had the highest flow (=cold water migrating to the hot tank).

Back in those days the reason for open tanks with automatic float-fill-valves were that they always kept having leaks out in the factory or in their machines and the tank systems coped better with high loss situations.

Viking, it is not really an issue for me but obviously there is an imbalance in the tanks as the cold (flow tank) is running at about a third to half full and the hot (return tank) is running near to full. The only issue for my client is detritus build up in the watercircuit and the present chillers have too low a capacity to maintain a 9 deg C flow temp.

The client wishes too remove the open vented system and I cannot really see a problem as long as the measured return temperture that he says is 16 deg C is true.

[Refrigerologist]

just thinking out loud here,

is it not possible to have an extra water vessel of lets say 2000ltr where the hot water returns to,make an evaporator like they use in beer-coolers,whit a small compressor unit,lets think 3,5 Kw ,use the same idea of beer-cooling, and then pump the pre-cooled medium to the return vessel before the chiller units,they are in cascade i presume,and then pump the medium or water over the chiller units.i think you can gain 4C° or 5C°, ......i think....:confused:

just an idea,

Ice

It's an idea, but it wont save any energy costs and will push up the install price.

I don't need to gain any cooling to the water, I just need to ensure that the return temperature does not exceed 1. the design limit of the chiller and 2. the point at which the chiller fails to lower the flow temperature to that required.

I may just install a larger buffer vessel so that I increase the system inertia and have a large resevoir of chiiled water.

I have allowed for a mixing valve with actuator to run from a temperature controller and immersion temperature sensor, but I was hoping not to have to install it.

[Refrigerologist]

Viking, it is not really an issue for me but obviously there is an imbalance in the tanks as the cold (flow tank) is running at about a third to half full and the hot (return tank) is running near to full. The only issue for my client is detritus build up in the watercircuit and the present chillers have too low a capacity to maintain a 9 deg C flow temp.

The client wishes too remove the open vented system and I cannot really see a problem as long as the measured return temperture that he says is 16 deg C is true.

Balance in the system should be maintained as both sets of pumps are actually working against the same friction losses. As water flow decreases around the actual load circuit it will increase proportionally around the chiller loop and vice versa. This is standard pumped water loop design.

I have allowed for a mixing valve to regulate the flow temperature so I will probably run the chilled loop a 7 deg C and the machine loop at 9 deg C. (Although I was hopng not to have to install it).

[icecube51]

I may just install a larger buffer vessel so that I increase the system inertia and have a large resevoir of chiiled water.

so if the cold water buffer is enlarged , its going to look like a kind of thermal storage principle ?? except there is going to be no spare time to fill it. (24/7/360).

Ice

[Refrigerologist]

just thinking out loud here,

is it not possible to have an extra water vessel of lets say 2000ltr where the hot water returns to,make an evaporator like they use in beer-coolers,whit a small compressor unit,lets think 3,5 Kw ,use the same idea of beer-cooling, and then pump the pre-cooled medium to the return vessel before the chiller units,they are in cascade i presume,and then pump the medium or water over the chiller units.i think you can gain 4C° or 5C°, ......i think....:confused:

just an idea,


Ice

2000litres of water! Have you worked out the cooling load for just a few degrees. I would end up with about 60 litres/kW of load, (including system water content), a bit excessive. I was thinking of increasing the buffer vessel to 400 ltrs from 200. This would give me around 13ltrs/kW.

[Refrigerologist]

so if the cold water buffer is enlarged , its going to look like a kind of thermal storage principle ?? except there is going to be no spare time to fill it. (24/7/360).

Ice

I don't see what you are saying. It is not thermal storage. I work on thermal storge at our dairy, it is a totally different principal. The use of a buffer vessel is to prevent short cycling of the compressor set. It is a store of water that smooths out the change in water temperature and nothing more.

Further to one of my earlier posts, I have just realised that the flow rate through the existing chillers may be too low or the strainers are blocked. From the information given to me today by the site engineer: 16 deg Hot tank temperature but a flow temperature from the chiller of 5 deg C. He probably doesn't actually need a larger capacity chiller at all! He probably needs me to take a look at the existing set up. I think the service company who are looking after the site have probably told them the existing chillers are too small, and we have provided a more competitive price!

[icecube51]

yep 2000ltr, should give the plant some time to reach the required Temp.the thermal storage principle is to get enough cold water at the time you don't really need it, so when the outside temperature increase you have enough buffer the take care of it.400 ltr is not exactly a big buffer for a 80 Kw chiller.

Ice

[Refrigerologist]

yep 2000ltr, should give the plant some time to reach the required Temp.the thermal storage principle is to get enough cold water at the time you don't really need it, so when the outside temperature increase you have enough buffer the take care of it.400 ltr is not exactly a big buffer for a 80 Kw chiller.

Ice

I am not after thermal storage. The principle does not apply here. I fully understand thermal storage. I installed 2 No. 400kW Daikin screw chillers operating at -10 deg C on a 50% glycol/water mix. (Each gives about 200kW capacity at those conditions). This operates on an off peak electrical tariff and saves the dairy upwards of £25,000 operating cost per annum. (Before anyone says it, I know screws are not the most effecient at those temperature, but I did not design it, that was the consultants error)!

In this case it isn't an 80kW chiller it is 2 x 37kW chillers operating as a run and standby. So 37kW total cooling at 7 deg C. 40kW at 9 deg C. A 200 litre buffer vessel is the recommended design size for this type of install. This has been sized, taking into account the water content of the whole system, which totals approximately 130 litres. Daikin suggets a 55ltr minimum circuit water content for normal A/C and 200ltrs for this application. In fact you can order the machine with a 55 litre vessel installed. I for one am not going to argue with Daikin! I was just a little concerned that the return water temperature might be excessive. I have not been to an injection moulding plant since I was 20 years old. We don't exactly have a lot of manufacturing industry here. A lot of bank workers, but no large industrial base. Anyway, I am going ahead with the setup I have designed and will install a mixing valve so that the water temperature is regulated more closely, especially as these chillers are controlled via return water temperature.

In this case there would be no real benefit for thermal storage as the low rate tariff is being fully utilised as the chillers will be operating day and night during those cheaper periods and there would be no guaranee that the 2000ltrs would not need to be chilled during the more expensive daytime period.

[US Iceman]

He probably needs me to take a look at the existing set up.


I'm wondering why you have not done this already????

What you are describing is what I was talking about before. If the flow rates are off, then the TD's will be off also. You could still do the calculations and say; see, it's the same capacity as the chiller possibly, but the end result is the temperatures are incorrect to meet the cooling requirements.

[Refrigerologist]

yep 2000ltr, should give the plant some time to reach the required Temp.the thermal storage principle is to get enough cold water at the time you don't really need it, so when the outside temperature increase you have enough buffer the take care of it.400 ltr is not exactly a big buffer for a 80 Kw chiller.

Ice

400ltrs for an 80kW chiller is more than enough for standard A/C. It may also be enough for process cooling if the water content of the water circuit is another 200ltrs.

How many l/kW are you allowing and on what design criterea do you base this? All the inforamtion I have read or been taught was base on 2 to 4 l/kW for A/C and 6 to 8 l/kW for process cooling.

[icecube51]

we had a plant where 125 people where working as designers. they all had a computer for auto-cad drawing and a laptop for calculating. each one of them had a 12m² of box office.
the problem was that the roof was steel-deck and the isolation was very poorly Lay. so when the came to work on Monday and the chiller was switched of it would take nearly 48 hours to get the right temperature.
we changed the 200ltr vessel for a 400 ltr and rearranged the electrics and thermostats. never had any complains sins then.

thermal storage is not only good for economics, its also very useful in extreme situations where nature dos tricks on us.

Ice

[icecube51]

400ltrs for an 80kW chiller is more than enough for standard A/C. It may also be enough for process cooling if the water content of the water circuit is another 200ltrs.

How many l/kW are you allowing and on what design criterea do you base this? All the inforamtion I have read or been taught was base on 2 to 4 l/kW for A/C and 6 to 8 l/kW for process cooling.

same thing as i was told, but times change and so is the machine design. we have to keep improving our selfs.

Ice

[chemi-cool]

Thermal storage is a good and useful method but...

It is expensive to install, it is only useful when the facility is closed for the night.

For office buildings it is the best solution.
For factories that run 24\7 it is useless.

[Refrigerologist]

I'm wondering why you have not done this already????

What you are describing is what I was talking about before. If the flow rates are off, then the TD's will be off also. You could still do the calculations and say; see, it's the same capacity as the chiller possibly, but the end result is the temperatures are incorrect to meet the cooling requirements.

I have not been asked to take a look at the equipment as I am we are not the company that look after the site, although obviously we soon will be. I will be speaking to the client in the morning and will suggest that the set up is checked over. But the production manager has the heat load requirements for the machines and the 20kW is not sufficient. Of course they are probably not getting the full 20kW anyway, but even if I were to acheive that it would still be short of the total load required during peak production.

[Refrigerologist]

we had a plant where 125 people where working as designers. they all had a computer for auto-cad drawing and a laptop for calculating. each one of them had a 12m² of box office.
the problem was that the roof was steel-deck and the isolation was very poorly Lay. so when the came to work on Monday and the chiller was switched of it would take nearly 48 hours to get the right temperature.
we changed the 200ltr vessel for a 400 ltr and rearranged the electrics and thermostats. never had any complains sins then.

thermal storage is not only good for economics, its also very useful in extreme situations where nature dos tricks on us.

Ice

Thermal storage will not apply here as the load is continuous 24 hours per day.. It is unlikely that we could build a sufficient ice bank during the off peak, unless of course we installed oversized chillers. Plastic production is 24 hours per day and so we would keep burning the ice off during the off peak hours.

In regard to the problem you have cited, you do not give any kW capacities, so maybe the designer never allowed for a big enough vessel in the first place. You also rearranged the thermostats, so maybe that was all it needed?

Also the problem you have cited is a common one that can be seen on a building management system. Many buildings I have seen actually become hotter after the staff have left the building. This is due to the air conditioning switching off and then over a period of hours, the electrical equipment, computers etc, and the fabric of the building give up their heat to the space and extreme temperatures are encountered. We have overcome this problem by switching the cooling plant on an hour or so earlier. In extreme cases we have had to switch the plant on for 2 to 3 hours on a Sunday to reduce building temperature because of high heat gains over a weekend.

But none of this has anything to do with my original question of closed loop cooling on injection moulding plant.

The only energy saving we would be interested in is free cooling, but client budget comes into the equation, not everything is cut and dried. I have been quoted an extreme amount of money for on board free cooling chillers. The client may well get his money back in 3 to 4 years, but if he hasn't got he money now then what am I supposed to do!

Space is limited as well so we cant easily have remote free coolers installed or an ice bank tank plus the extra pump sets required would eat up a lot of space that we just don't have!

[US Iceman]

But the production manager has the heat load requirements for the machines and the 20kW is not sufficient. Of course they are probably not getting the full 20kW anyway, but even if I were to acheive that it would still be short of the total load required during peak production.


My point is; don't take someone's answer as the truth. He may be giving you the same data he gave to the last firm who is now possibly on their way out.

The way to prevent surprises (yours or theirs) is to check the data...

If the new chillers don't work....who gets the credit?

[Refrigerologist]

My point is; don't take someone's answer as the truth. He may be giving you the same data he gave to the last firm who is now possibly on their way out.

The way to prevent surprises (yours or theirs) is to check the data...

If the new chillers don't work....who gets the credit?

I know what you are saying Iceman, but the production manager is a friend of mine, so I don't think he will be trying to screw me! I will be talking to them tomorrow, as I am going to try and get them to increase the budget by the small amount of about £45,000.00 so that they get top of the range, free cool chillers. Also my original quotation does state that the chiller ratings have been selected using the heat load data provided by the client. So I am covered.

As I say the only thing I was unsure of was closed loop on injection moulding, but I have spoken to some of the manufacturers techies, and they say no problem!

[Refrigerologist]

Hello guys

I had a little more information from the site engineer today. It appears that the process pipe work is not actually a normal flow and return set up. It is actually fed via a pressure pump set up and not circulators! Chilled water is pulled from the cold tank and flows into the flow ring main which is in a complete loop, there is no direct return pipe work. The chilled water path is as follows:

The chilled water flows into the flow ring main under pressure, the water then flows through the mould tools and from there enters a separate return loop and flows back to the warm tank. As each mould tool is closed down, the flow through each machine decreases and the flow pressure rises. As the pressure rises a spring activated bypass valve opens and water is vented from the flow ring main into the return ring main and back to the warm tank.

It appears that these machines require a substantial pressure differential for flow to occur through the mould tools.

I was under the impression that I could close the loop and use the pumps to circulate chilled water in the usual manner with a flow and return set up. I had assumed the differential pressure created by the pump would be enough enduce adequate flow through the machines.

So it is back to the drawing board and I WILL GIVE MYSELF A SLAP FOR NOT SURVEYING THE CURRENT SETUP IN ENOUGH DEPTH!

[US Iceman]

As the pressure rises a spring activated bypass valve opens and water is vented from the flow ring main into the return ring main and back to the warm tank.


That in itself is a waste of energy. A better solution is use a VFD with a pressure transducer to slow the pump down when the pressure begins to rise.

The underlined section I question also. If you dump cold water back into the return side that can potentially lower the LMTD that might be available for the chiller.

One question: what is a flow ring?

[Gary]

The chillers are delivering water at 5 deg C to the cold tank, but the cold tank is actually at about 14 deg C, this is because it has 2 balancing lines directly connected to the hot tank. The hot tank (return tank) is receiving water back at about 16 to 17 deg C.

The delta-T across the chiller is apparently 11-12K, clearly indicating insufficient water flow. You might check the strainer. Less likely, but possible, if the pump is 3 phase it could be running in reverse.

[Peter_1]

Just joining this thread and not read everything thoroughly , if it's an open circuit, then probably you have also fungus and some sort of gelly inside the tubes.
The plastic granules are covered with some sort of white gliding powder. This gliding powder is mostly organic.
Due to the ideal warm temperatures, this powder 'transforms' to some sort of gelly and blocks strainers and tubes in heat exchangers.

I should also follow the advice of USIceman, never follow for 100% what someone is telling you. Take out a story or arguments what can be useful to solve the problem. If they don't give enough information, it's up to you to ask the proper questions.
This has nothing to do with the fact that he's your friend or that he's trying to screw you up. Your friend can think that these are the right values, these values can come from another, he's saying this to help you but believing everything for 100% is wrong.
Besides, your friend is not a refrigeration tech, it's up to you now to prove you are the right man on the right place and check what's really needed and then see what's already installed. You then can conclude if there's not enough capacity.

We install for such an application a 3 way mixing valve and VFD controlled pumps.

[Refrigerologist]

That in itself is a waste of energy. A better solution is use a VFD with a pressure transducer to slow the pump down when the pressure begins to rise.

The underlined section I question also. If you dump cold water back into the return side that can potentially lower the LMTD that might be available for the chiller.

One question: what is a flow ring?

RE: Flow ring

I had never seen a set up like this one. I have a drawing but unfortunately my scanner is busted!
So I will try to explain the flow:

1. The process pump pulls water from the cold tank, the water flows into the process chilled water ring main. This make a complete loop of its' own. There is no direct return water pipe from this ring main!
2. Water flows into each machine. The heated water flows into a process chilled water return ring main. This ring main is a complete loop of its' own, but has the addition of a pipe 'teed' into it, this pipe returns to the warm tank.
3. Installed between the flow ring main and return ring main is a pressure control valve. As each machine closes down and the pressure increases in the flow ring main, a spring controlled bypass valve opens and allows water from the flow ring main into the return ring main. The water is returned to to the warm tank.
4. The chilled water units are piped so that water from the warm tank is pumped through the chiller heat exchanger, is chilled, and returned to the cold tank.

[Refrigerologist]

The delta-T across the chiller is apparently 11-12K, clearly indicating insufficient water flow. You might check the strainer. Less likely, but possible, if the pump is 3 phase it could be running in reverse.

Gary, I had already covered this in a previous post. We are aware of the lack of flow. This is the main reason for wishing to make the system a sealed and pressurized.

The heat exchangers are full of scale. There are no end plates and the only options are to carry out an acid clean.

However the client requires 40kw of cooling per chiller and those installed are only 22kw rated. So we are not persuing repairs. They undertake the cleaning of the heat exchangers themselves.

The water is filtered and the filter is regularly cleaned.

[Refrigerologist]

Just joining this thread and not read everything thoroughly , if it's an open circuit, then probably you have also fungus and some sort of gelly inside the tubes.
The plastic granules are covered with some sort of white gliding powder. This gliding powder is mostly organic.
Due to the ideal warm temperatures, this powder 'transforms' to some sort of gelly and blocks strainers and tubes in heat exchangers.

I should also follow the advice of USIceman, never follow for 100% what someone is telling you. Take out a story or arguments what can be useful to solve the problem. If they don't give enough information, it's up to you to ask the proper questions.
This has nothing to do with the fact that he's your friend or that he's trying to screw you up. Your friend can think that these are the right values, these values can come from another, he's saying this to help you but believing everything for 100% is wrong.
Besides, your friend is not a refrigeration tech, it's up to you now to prove you are the right man on the right place and check what's really needed and then see what's already installed. You then can conclude if there's not enough capacity.

We install for such an application a 3 way mixing valve and VFD controlled pumps.

Peter

The client has expanded the operation from 12 injection moulding machines to 19. The new machines are larger capacity and the heat load has almost doubled.

The problem is more to do with scale build up and not so much algae or debris. Treatment of the water is not an option and strainers are also not going to stop scale build up.

The client, his production manager and the injection mould engineer are all insisting that these machines require a high pressure differential between the flow and return pipes to induce enough water flow though the mould tools. I am not going to argue with them, they have factories in many counties making medical items such as oxygen masks. Should I ignore their advice and install the more usual chilled water lop set up with either variable flow pumps or standard pumps and mixing valves and we don't get enough water flow, I think I might just get sued to bankruptcy!

[Gary]

Gary, I had already covered this in a previous post. We are aware of the lack of flow. This is the main reason for wishing to make the system a sealed and pressurized.

The heat exchangers are full of scale. There are no end plates and the only options are to carry out an acid clean.


At this point I see no evidence of scale build up, unless you are running a very low SST (high approach). What I see from the data given is a flow problem, not a scale problem.

[Gary]

RE: Flow ring

I had never seen a set up like this one. I have a drawing but unfortunately my scanner is busted!
So I will try to explain the flow:

1. The process pump pulls water from the cold tank, the water flows into the process chilled water ring main. This make a complete loop of its' own. There is no direct return water pipe from this ring main!
2. Water flows into each machine. The heated water flows into a process chilled water return ring main. This ring main is a complete loop of its' own, but has the addition of a pipe 'teed' into it, this pipe returns to the warm tank.
3. Installed between the flow ring main and return ring main is a pressure control valve. As each machine closes down and the pressure increases in the flow ring main, a spring controlled bypass valve opens and allows water from the flow ring main into the return ring main. The water is returned to to the warm tank.
4. The chilled water units are piped so that water from the warm tank is pumped through the chiller heat exchanger, is chilled, and returned to the cold tank.

This would probably make sense if, and only if, I knew what a ring main was. Not having a clue, the above makes no sense at all.

[icecube51]

i think i start to understand the set-up,but is it not possible to post a drawing of some kind,so we can make note's and idea's and send it back??? i think that everyone will understand it much better that way,and you can pick the best of choices.

Ice

[Refrigerologist]

At this point I see no evidence of scale build up, unless you are running a very low SST (high approach). What I see from the data given is a flow problem.

Gary you have not been on site! I have, the flow is next to nothing through the heat exchanger.

The tubes are probably clear and the scale has built up around the ends before water has a chance to enter the tubes. I have had this problem many times both on water cooled condensers and chilled water evaporators. Hence the low leaving water temperature and poor flow. You are confusing the issue!

Some of us do actually know what we are doing! i am asking for advice on what to do with an open system of unusual design. I was not here for debate on flow rates, capacities etc:D. The chillers are knackered. They are undersized, they are no longer required by the client. Could we please stick to the request for help in closing the system if that is possible?

[Refrigerologist]

This would probably make sense if, and only if, I knew what a ring main was. Not having a clue, the above makes no sense at all.

A ring main is a circuit that leaves and returns to the same place making a complete loop.

An example in UK wiring is for 13 amp socket outlets for appliances. A 3 core cable, (L,N & E) are connected into the distribution board. The live at the circuit breaker, the neutral at the neutral bar, and the earth at the earth bar. This cable is run from socket to socket, finally returning to the distribution board and connected in the identical points as above. This constitutes a ring main. Effectively 2, 3 core cables feeding all sockets and increasing the amount of amperage that may be pulled through a relatively small cable. For instance 32 amp@ 240v on a 2.5mm cable.

In this instance it is a 3" pipe completing a circuit with a pump teed in at one point.

I hope that makes sense:p:p

[Refrigerologist]

i think i start to understand the set-up,but is it not possible to post a drawing of some kind,so we can make note's and idea's and send it back??? i think that everyone will understand it much better that way,and you can pick the best of choices.

Ice

Sorry, my scanner is broken so I cannot upload the schematic. I have tried to explain it as best I can, but it is hard to follow. I have not spoken with any body, and that includes companies who deal mainly with process cooling, who have come across this set up!

[Refrigerologist]

That in itself is a waste of energy. A better solution is use a VFD with a pressure transducer to slow the pump down when the pressure begins to rise.

The underlined section I question also. If you dump cold water back into the return side that can potentially lower the LMTD that might be available for the chiller.

One question: what is a flow ring?

Iceman, I could not agree more about the waste of energy, I would love to use variable flow, but if you look at my previous post, (after your one on this subject as I missed this one), the client is insisting that they need a high pressure differential for flow accross the tool heads. I have not heard of this requirement before, and nor has anyone I have spoken to. The installed pumps for the process side are not circulators but are 2 stage pressure pumps! Personally I feel the requirement may have been misunderstood by the original installer!
I think I may have to contact the injection machine manufacturer and confirm the actual worst case pressure loss for each machine tool. Then as per usual, if I install the correct pumps, there should be no problem other than back pressure which we can control with variable speed drive.

[Refrigerologist]

Guys

I would like to make you aware of water problems that we face in Guernsey.

Domestic water in this area has a pH of about 7.1 to 7.6, slightly alkaline. It contains quite a lot of lime scale.

I have been on several sites where a 4" incoming cold water main serving a school, prison or large office has been almost blocked with scale build up. About 5 years ago we replaced a number of 4" valves that had only a 3/4" hole left in which to pass mains water. The dinner ladies at the shool had to fill every pot and pan they had with water, if lunch prep time coincided with the kids taking showers!

The local government plumbing department failed to find the problem in 2 years of trying. They assumed the valves were ok!

So from this you will see that scaling can and is a big problem even where cold water is concerned and especially where there is a continual replenishment of nutrient, lime scale, iron etc, in the water.

[US Iceman]

...the client is insisting that they need a high pressure differential for flow across the tool heads.


That may be, if the molds are not designed for sufficient water flow to provide adequate cooling. Therefore, if the mold flow paths are restrictive then the only way to gain cooling is push more water through at higher supply pressure.

I have not seen this before on the projects I have worked on as all had single stage centrifugal pumps.

Is the water quality is as bad as you say, then a closed loop with treated water would be an immensely better solution.

[icecube51]

maybe consider "reverse osmosis" water?
and as i understand,is when the chilled water entering the mould machine,it become so hot that it would return instead of going forward,so you have to install or very heavy circulation pump or heavy duty pression pumps?

Ice

[Peter_1]

I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.

[Peter_1]

Perhaps this can help
www.mcquayservice.com/mcquaybiz/literature/lit_systems/AppGuide/AG_31-003-1.pdf -

[Gary]

Gary you have not been on site! I have, the flow is next to nothing through the heat exchanger.

The tubes are probably clear and the scale has built up around the ends before water has a chance to enter the tubes. I have had this problem many times both on water cooled condensers and chilled water evaporators. Hence the low leaving water temperature and poor flow. You are confusing the issue!

Some of us do actually know what we are doing!

Don't take it personally. There are other people watching and learning. They need to know which symptoms indicate flow problems (delta-T) as well as which symptoms indicate scale build-up/heat transfer problems (approach).

[Peter_1]

Was thinking th same Gary.

[Gary]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.

Does that sound about right?

[icecube51]

and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

make sure they are strong enough to overcome the going pressure rate.:rolleyes:

Ice

[icecube51]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the cold ring/loop to the hot ring/loop.

Does that sound about right?

is there not going to be a chilled water tank needed?

Ice

[Gary]

is there not going to be a chilled water tank needed?

Ice

I'm thinking that's the "cold tank".

On the other hand I may be entirely wrong in my understanding of how the system is piped?

[icecube51]

sorry Gary ;-{

[TRASH101]

From your description of the system it should be possible to close the system but is the existing ring (which I believe is acting as supply buffer tank/ low pressure header) big enough to take the new load and is it likely that all the injection circuits will be running at once.

The warm tank could pose more of a problem because if you upgrade the chillers then you`ll definately have to up the flow rate which will mean you might end up drawing off from the cold tank to maintain the warm tank under low load conditions.

I can see why it is designed as an open system and closing it without a complete redesign may prove to be..............interesting:D

It would be really helpful if you could draw up a schematic.

[TRASH101]

Its making a little more sense now

I think if you look at just the chillers, cold tank and warm tank as being the primary circuit and close it as you would any normal chilled water circuit the the take off from the cold water tank must be big enough to compensate for no warm return from the process (might need a one way valve in it) work out if you need an expansion vessel on the warm tank and or invertor drive your pump feeding the chiller from the discharge to ensure your vol remains constant, depending on system characteristics the cold to warm take off might want to have a modulating valve on driven by cold tank pressure.

Hope that might put you on the right path. Its a bit difficult to say without seeing the system and shed loads of calcs.

Don`t forget that if youre going for vt on the process take offs then you need the temp diffs for the process water to size and select your valve arrangement.

[Iceman1956]

Hi Refrigerologist Only just picked up on your post, and have quickly scanned what has been said.
There are two points that do not seem to have been asked or questioned. Your existing chiller are likely to have shell and tube evaporators ? the new chillers you are looking at will have Plate type heatexchagers ?
The second item is are you keeping a primary loop through chillers and back to the buffer tank ?.
Providing the primary and secondary loop feed directly from the buffer tank you will not have any problems with a sealed system, as any imbalance is cancelled out within the buffertank. We have completed many such modifications over my 35 years in process cooling, with no problems.

Ensure New Pumps match design flow for new chillers as Plate type HeatX have greater PD across them from Shell and tube.
Flow to process should be from base of buffer tank, as should the return from chiller. Flow to chiller should be from top of buffer tank as should the return from process.

Hope this helps.

[Refrigerologist]

Thanks for all the ideas and assistance.

I have since spoken with the guy who originally designed the system! He has told me that in order to ensure that the water temperature at each mould head remains constant, the chilled water loops are fed via pressure pumps and the flow pipe is a complete loop. The return water path is via each mould head unless the pressure increases to a point where the spring loaded pressure relief valve opens and allows water to flow directly to the return circuit.

He has advised us not close the system due to balancing problems.

We are going replace the existing plastic water tanks with GRP insulated tanks and install process chillers with shell & tube heat exchangers. We will be recommending water treatment of the ingoing make up water to help prevent scaling in the tubes.

[Refrigerologist]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.

Does that sound about right?

Sorry for not replying earlier, but I have been on holiday in Ireland, and the Guiness has been good!

Yes, I think your despcription is about right. It may be a bit academic now as we have decided to keep with an open system but treat the make up water.

[Refrigerologist]

I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.

I haven't been arguing with my client. What makes you think I have been? They asked if we could close the system. We said we could, every one I have spoken to says we can, now the client is no longer sure and does not understand fluid dynamics very well. So we have decided to leave it as an open system and treat the water instead. A far easier install, but actually more expensive as we must now use shell and tube heat exchangers in place of plate type.

Thanks for all the ideas and advice though!

[Electrocoolman]

Hi Refrigerologist and guys,

Have just picked up on this thread and one thought has occurred to me....with reference to the supply loop.....

Although the supply ring is pressurised by the pressurisation pumps (which should be VSD controlled in this day and age) the water in the supply loop will surely have a temperature variation around it, as there is no mention of a circulator pump, and as you mentioned machines being turned off....will not the flow and thus temperature vary according to demand? Maybe this is not percieved as a problem?....perhaps the loop is only small?

You mention project costs are tight and funds limited....are there any goverment tax incentives on Guernsey for energy saving projects (as on the mainland)..?.(ie Enhanced capital Allowance)...just another thought!

[US Iceman]

He has advised us not close the system due to balancing problems.


How will the system be closed if it has storage tanks in it? The tanks will most likely be open to atmosphere, but the piping would essentially be a closed loop (except hydraulically).

[Magoo]

Your initial major problem is the water quality, as in high calcium content, (hard water). I would definitly recommend converting to a closed loop water system, with high circuit flow rates and a high water chiller by-pass rate. In effect the chiller is trimming the loop temperature, and the low delta tee system water is doing the work. You must add to system a pressure compensation vessel on the primary pump circuit to handle the changes in system and elliminate pipe hammer, the heat exchangers at the moulding machines should have rapid response 3 way by-pass vavs. then you maintain a constant loop volume flow.
First thing to address in the obvious scaling problem in existing system. Ridlime is an excellent product, and eco friendly, add lots of flushing. Next is the problem with closed circuit water cooling systems is the water quality and PH control. Basically you have a perfect low voltage battery, as in dissimilar metals and temp variations and an electrylite (water), so PH and water conditions are important. Cathodic corrossion is un-cool and can send companies broke, because all of a sudden everythings is leaking water and the refrig system is full of water, result no production and huge repair and recovery costs.
Down the track a bit you should recommend a dry cooler with water additions to elleviate the chiller loads, depending on local ambient conditions and wet buld conditions.
magoo

[brunstar]

you will be best to use one buffer tank so that you are constantly mixing the water down through the chiller, otherwise it will be too high on the return to the chiller.
So basically buffer tank flow and return to the moulds then flow and return to the chiller.

[Refrigerologist]

Hi guys, an update is long overdue!

Thanks for the comments and advice.

The client has now gone out for a requote, and I am not hopeful of getting the job, but that could now be a blessing!

Anyway the contractor who has now quoted has chosen a plate heat exchanger system on the same open loop system, so I am expecting them to have some serious problems as the water is not treated and the old shell and tubes are fouled with scale deposits!

[US Iceman]

You may be thankful you don't get the job. Loosing a job is bad enough. Getting a bad job can be even worse.;)