I recently received an e-mail from BV Thermal Systems, a supplier of chillers, that caught my eye. It opened with a statement that is all too familiar in our world of temperature control:
“Determining the right size for your chiller does not mean, will the chiller fit into a specific space. That is important, however, determining the right size chiller is really about will the chiller cool my process?”
They then go on to review how to size a chiller for the process thermal load. With this information, the physical size of the unit can be determined.
More Than Chillers
Though we also often use chillers in our systems, the size problem applies to just about every part of the system, yet the same rules apply. But there are a few factors that determine system size. First, of course, is the thermal load – how much heat is required on the coldest day at the highest process rate, and how much cooling is required on the hottest day at the highest process rate. This will determine the size of the heating and cooling systems required. But often overlooked and usually more important is the actual thermal transfer area required to add or remove the energy from the process itself.
So why would this be more important?
No Prior Planning
If you’re reading this, you’re probably already aware that Saint Clair Systems focuses on the point-of-application or point-of-dispense or point-of-use – whatever you want to call it. This means exchanging the energy to maintain the temperature at the “business end” of the system rather than the beginning – and this is where space is usually the most limited.
This is less of an issue in a greenfield project where this can be incorporated into the building design up-front. But many, if not most of our projects are retrofits – being added to existing systems. When these systems were designed, they were thought to be “complete systems”. Nobody thought that someday, somebody might want to add temperature control to manage viscosity, so naturally little, if any extra space was provided because floor space is expensive! This means that adding the system is likely going to come with some space challenges.
So How Big is Big Really?
This is always a loaded question. Primarily because it does depend on the thermal loads the process will generate – much like the chiller example I opened with. In truth, our equipment ranges in size from small thermoelectric units the size of a breadbox 16”(40cm)L x 14.5”(37cm)W x 12.5”(32cm)H, weighing as little as 30 lbs. (13.5Kg) to skids that are 13’(4m)L x 10’(3m)W x 8’(2.5m)H, weighing as much as 10,000 lbs. (4500Kg). That’s a pretty wide range!
But even the smallest system may be too big to get right to the point-of-use.
This means getting creative in our system design…
When All Else Fails, Work With What You’ve Got
The beauty of a fluid-based thermal transfer system is that you can move the energy over a reasonable distance with a minimal loss of control. This also makes it possible to use the surfaces already in contact with the material to be controlled – in other words, convert existing surfaces into thermal transfer area. Exploiting this option, SCS has been fortunate to secure several patents for devices that do exactly that. Coax hoses, traced covers, traced blocks – all are space efficient ways of controlling temperature at the point-of-use without consuming valuable real estate. This also keeps the devices out of the operator’s way by following existing tubing paths.
Sense Carefully – Control Locally – Mount Remotely
Another key piece of the puzzle is where to sense temperature. There are many options but selecting the right one is one of the most important factors in attaining effective control. It’s not always possible to place the sensor right at the point-of-use. And what options you have are often dictated by the thermal transfer systems you are using. It is a delicate balance and requires a bit of experience.
This method of implementing thermal transfer and temperature sensing allows us to mount the larger heating and cooling equipment remotely from the process where there’s room for it. Modularity helps too. We often separate our chiller system from our heating and temperature control systems to allow them to each be smaller in size and located where it is most efficient.