Ensuring optimal performance and meeting processing goals with your heating and cooling system involves careful attention to key details, particularly the size of the system. In this blog, we’ll delve into the crucial aspect of sizing by using a chemical mixing company as an illustrative example. In this case, we’ll be exploring the needs of this customer with a jacketed vessel, or double-walled tank. While your end product may differ from theirs, the process and calculations we’ll be using are typical of many process applications.
Scenario
A chemical mixing company, previously relied on an aging central hot water boiler and chiller to regulate the temperature of their chemicals. However, evolving market demands and stricter recordkeeping necessitated a more precise temperature control system. The old systems, lacking programmable electronic controls, could no longer meet these requirements.
The application of a jacketed vessel, or double-walled tank, was ideal for achieving the specific sequenced intervals necessary for developing the customer’s end product. The company used water and a small amount of ethylene glycol as a heat transfer medium, with the glycol serving as both a biocide (a product used to kill or control the spread of harmful microorganisms like bacteria and viruses) and protection against freezing.
Remember: When using glycols, allowances must always be made in the heating and cooling load applications. This is because glycol inhibits water’s ability to efficiently transfer heat. The amount of glycol in the system will reduce the system’s heating and cooling capabilities depending on the percentage of glycol mixed into the water.
Process Specifications
Because the insulated jacketed vessel was relatively small, the exothermic or endothermic reactions were minimal and therefore not included in the heating and chiller loads calculation in the table above.
Calculating
Once the kilowatt requirements were established, surface losses from the temperature control unit must be considered for operating temperatures above 200ºF (93ºC). Below 200ºF, losses are generally negligible, influenced by factors like surface temperature, materials of construction, ambient temperature, and circulating fluid temperature.
When required, multiply the heat loss per square foot by the surface area to get total watts at the desired operating temperature. Convert it to kilowatts and add it to the process requirement.
Additionally, a safety factor should be added to the final calculation for assurances of coverage for unexplainable items not previously considered.
Once the requirements were calculated, the temperature control system manufacturer recommended a 21 kW heater. This size unit accounts for system surface losses and derating due to a 15% glycol/water mix. It also accounts for any line losses due to uninsulated, exposed surfaces outside the temperature control system.
Company X also required the ability to cool their product in 10 minutes.
Because 1 ton of cooling equals 12,000 BTUs, and to account for derating due to the glycol, the customer determined that the most appropriate selection was a 10-ton chiller.
To Conclude
While this customer’s specifications may differ from those of other companies, the process of calculating heating and cooling requirements is universal. For effective process control requiring both heating and cooling, consider a temperature control system from Mokon.