How a Chiller, Cooling Tower and Air Handling Unit work together

Hi there Paul here from the engineering mindset calm in this video we’re going to look at the basic operation of a centralized chilled water system and this is very typical in in office buildings all around the world and we’ve got a little model here of a basic built office building stripped of all its insides and if you can imagine normally these floors will be filled with people and computers the server rooms and it’s going to generate a lot of heat especially when the Sun is beating down on the building in the middle of summer so this building is going to have to produce a lot of cooling to handle that heat and keep the inside of the building in a very nice temperature so how does it do that well you need some plant items first and in this very typical setup we’ve got a chiller here along with the distribution pumps the air handling units and the cooling tower which is up on the roof so the chiller is the the producer of chilled water in this system and the chiller has two main cylinders one is the evaporator here and that’s where the chilled or cold water is produced and the other cylinder is this at the back here which is the condenser which is the condenser silver and that is where the heat of the building is sent oh it’s collected and sent to the the cooling towers now a real cello will look something like this we have the evaporator the chilled side which is in this case all insulated to keep that cool cool thin side and then you’ve got the compressor on top as well as the power supply and the control to the system as well this is a centrifugal chiller there’s lots of different types which we will go into detail in this video I just need to understand the basics of how this building is called so the chilled water leaves the evaporator and it’s pulled out in this instance by the by the pump sometimes it can be pushed in in this case it’s being pulled out it’s depending on the system and the design of the chiller and you’ll notice that I’ve covered these pipes in one of the dark blue that’s for leaving the evaporator and I put a dark blue so that you know that it is a much cooler temperature so this is leaving at about 8 degrees something may or may be 6 to 8 degrees and is leaving in this design at 54 liters per second the other pipe the lighter blue one that is so you know it is a higher temperature and in this instance it’s about 14 degrees Celsius we have 12 to 14 maybe you look very higher maybe lower it all depends on the design of the system and the load of the building in the in the real world though these these pipes will not be this color then they could be but they’ll unlikely to be in the real world they will look something like this and you’ll you can see here we’ve got chill CHW chilled water flow and an arrow so you obviously understand where it’s going and chilled water returned we’ve set the pretty standard color bands and arrows and labeling system there and this is in almost every plant room you’ll find the pipe to be labeled and note noted this way but for illustration purposes I’ve just covered them in here so you get a better understanding of what is happening in the system so the pump is pulling this chilled water about eight degrees and it is sending it up into the riser a real-live pump looks something like this this is the direct coupled centrifugal pump with the motor on the back here and then it’s coupled straight on to the pump here which is under some installations you can’t see it unfortunately in this photo but that chilled water is sent up into the riser which this pipes here and they that riser those risers rise the height of the building and branching off of the risers are some feeds flow return into these which are air handling units in the real world the air handling units will probably look something like this this is a very small example there are much larger designs and even smaller units than this as well but it all depends on the design and the load of the building here we’ve got the flow returned and it’s going into the coil here which I’m going to explain about just shortly and we’ve got one coil here for heating and one for cooling as well which I’ll talk about next so the air handling unit its purpose is to take the warm air within the office floor we it gets pulled in through a fan and that fan then rejects it out the other side and it’s distributed off through some ductwork often various points in the office to where it’s needed and inside this air hanging unit is a coil and the coil looks something like this in the real world and chilled water enters the coil and makes its way up for always little little loops here and then back out the top here so that enters at about eight degrees in this example and by the time it reaches the top there it’ll leave that cooling coil at about fourteen degrees so that rising temperature is the result of the air which is passing through this air handling unit cooling down so the warm air enters it hits this coil the coil transfers it’s cool into the air and the air transfers its heat into the coil the air leaves at a lower temperature and the water then leaves at a higher temperature the air handling units they could be one per four there could be multiple per for all it could be one on the flow here and the ductwork serves the number of floors below and this is just illustration purposes to just help you understand that so that a chilled returned water goes back into a riser and that is fed back down into the evaporator of the chiller inside the chiller is a separate system which is running around between the compressor the condenser in the evaporator as well as the the vane guide at the bottom there and that is a refrigeration cycle happening in there and what’s happening there is the heat within this pipe here though is being carried away by the refrigerant and sent into the condenser where it can dump its heat and be taken away to the cooling towers inside the chiller it will look something like this so we’ve got the evaporator side here the cooler side and the condenser side here as well as the compressor and the vane guide at the bottom there so the refrigerant is just flow around this system here transferring that heat from one side to the other and going to another continuous loop we’ve got some other videos on the refrigeration cycle if you want to learn more just check out our videos so now that the heat in this pipe here has been transferred over to the condenser side the condenser then sends this water which is now it’s just now called the condenser water and sends that up to the tower and in this instance I’ve colored this pipe red so that you know it’s a higher temperature and in this example that’s good it’s about 35 degrees Celsius OC and it’s for the flow rate of about 58 litres a second as well being sent up to the cooling towers that can change us it’s just on this design for illustration purposes and we’ve got the condenser return water here and in this example it’s about 28 degrees so it’s lost in atomic is up to the cooling tower and comes back it’s lost about 7 degrees in this instance that’s at design though in rip in the real world it may not be as high as that in the winter it wouldn’t would be much lower to but yesterday in the real world the condenser the pipe work it looks own like this so oh sorry that’s the wrong one that’s children to return it will just say condenser water here and we’ll have some markings on colors there I’ve used the wrong image apologies so that warm condenser water is sent up to the cooling towers on the roof of the building and in this instance it’s and open cooling tower so that means that the warm condensed water enters into the cooling tower and is sprayed and that spray is then runs down the inside of the cooling towers collect at the bottom running in the opposite direction is some is air being pulled by these fans here and that these fans pull the ambient air outside the building into the cooling tower and out up through the top in that process this warm condenser water will lose some of its heat and the air entering and leaving this cooling tower will it will leave a much higher temperature than when it came in it also left with some moisture so the relative humidity will have increased as well a real cooling tower looks something like this this is the bounty more air coil company this is a very typical cooling tower you’ll find on the roof of lots of buildings and just to give you an idea I’m not familiar with cooling towers this is New York City and as you can see almost every building here has cooling towers of one size or another some more than others it all depends on the size of the building and what’s happening inside there as well but they are on every big building in pretty much every city around the world so once this cooling tower has lost about seven degrees in the cooling process is collected at the bottom and it is sent back down to the condenser pump and that is then pushed back inside the condenser I’ve actually put this pump run the wrong way there that’s obviously coming out there should be the other way we pipe the other way but this is the free video so I’m not great together and yeah so this is where the the water the condenser water then comes back into here enters into these coils inside and picks up more heat and is sent back up to the cooling towers it’s important to note that this system here the condenser water system and the chilled water system are completely separated they do not interact they do not swap the water in between it is just the refrigerant that what happens in the refrigeration cycle between these units that’s the only thing that passes between them the water in here is sealed in tubes and and leaves again those pipes also in this instance we’ve got one plant item and my plant item I mean that a mechanical asset in the real world it’s unlikely you’ll have just one you’ll probably have n plus 1 so n whatever you need you have that number plus 1 because if this item here was the break or say this pump here was the break then we wouldn’t be able to produce called walk cooled water or condenser water and we wouldn’t be able to cool the building down so we’d always usually have at least two units then ill operate in duty and standby so only one plant item will operate at any one time and they will probably rotate their duty so that this pump will run for a week and the other one but then learn for the week afterwards and swap vice versa and that also allows you to carry out maintenance on the system as well on large buildings you’re more likely to have a more much more complex system than this you’ll have two three four chillers maybe even more than that and a lot more air handling units and cooling towers or bigger cooling towers and the complexity of the system is completely based on the load of the building you might even have a number of separate chilled water systems you could have a system which deals with critical so it’s generator fed and it supplies only the server rooms because they need cooling 24/7 and you’ll have this common a centralized system which handles there’s the space temperature within the floors but this is a very basic overview and we’ll go into more complex systems in later videos but thank you for watching and please check out our others