The administration building of your multi-building production facility is about 20,000 square feet. It’s heated by a set of dual-stage gas furnaces. It also has a set of heat pumps, which were installed 24 years ago. The system was originally set such that the heat pumps would not operate below about 50℉.
Last year, the plant engineer had the setting changed to the other end of the operating range. Consequently, the gas bill was down considerably, but the electrical bill was up considerably. The cost of heating, in net, was up considerably. And people complained they weren’t comfortable.
The plant engineer now is not convinced the setting change was the cause and convened a meeting to discuss possible causes. The mechanical maintenance engineer is convinced that the heat pumps should be taken out of the system, stating it costs less to heat with gas than with electricity. The plant manager believes that poor maintenance resulted in the increased cost, citing “obvious inefficiency as evidenced by the fact people weren’t comfortable.” Opinions were all over the place.
The plant engineer called you into his office and asked you to do two things:
1. Get an HVAC firm to diagnose those systems and fix anything that’s wrong.
2. Determine the best mix of heat pump and gas, specifically where to set the temperature boundary.
What information should you provide to the plant engineer in your report?
Answer to Quiz. First, you should probably lay out some key facts. For example:
- Using a heat pump is not “heating with electricity” in the sense that heating with resistance coils is. Electricity is needed to drive the compressors and fans, but it’s not used to produce heat.
- Heat pump technology has changed dramatically over the past 24 years — and decidedly for the better.
- The existing heat pumps probably were not an efficient choice below about 50℉, but modern heat pumps can efficiently transfer heat from much lower outdoor temperatures.
- Modern controls can eliminate the need for guessing at the temperature boundary.
- The existing heat pumps are old and probably due for replacement.
- Discomfort of the occupants isn’t necessarily due to poor heating. It can be due to poor air circulation or such things as new gaps in the building envelope. It can also be due to problems with the gas furnaces.
Next, you should propose that the following actions be taken:
- Thermographic inspection of the building envelope.
- Visual assessment for barriers to air circulation — for example, tall filing cabinets positioned in front of cold air return vents or in front of intended warm air paths.
- Once any errors revealed by visual assessment are corrected, then a thermographic imaging of the warm air flow should be conducted.
- Collect bids for replacement of the existing pumps, with the intention of using the information in a capital expenditure request.
- If an HVAC firm has not already been performing semi-annual maintenance on the HVAC system, hire a HVAC firm to perform the testing involved in such maintenance. In either case, review the reports with the HVAC firm to assess the condition and life expectancy of the existing system.
When you’re trying to optimize infrastructure such as HVAC (or lighting) for cost, performance, and reliability, it’s never as simple as choosing one technology over another. When you have an existing system where one of these three attributes is below expectations, you must assess the environment in which the system operates. You must also ensure that people who have influence on the decisions are working with the correct information instead of outdated perceptions, and that is often the single biggest challenge in the optimization process.
