System Model, Performance Improvement, Heat Pump
Improving Performance of an Existing Heat Pump: A Case Study Vijay Bahel, Scott Lanzer and Suresh Shivashankar Emerson Climate Technologies Sidney, Ohio 45365, USA Phone: 937-498-3643, Fax: 937-498-3203 Email: Vijay.Bahel@EmersonClimate.com Abstract This paper presents the findings of a case study used to identify the design options for upgrading the performance of an Air Source Heat Pump with minimum design changes to the system chassis. We used Emerson’s Steady-State System Model to identify opportunities for improving the baseline SEER. Our starting point was a nominal Fixed Capacity 5 ton, 14 SEER Heat Pump using Refrigerant R-410a. In this exercise we identified opportunities to improve SEER by selecting a Variable Speed: (i) Compressor, and (i) Indoor and Outdoor Fans. These changes are relatively easy to implement and don’t require changes in the indoor and outdoor heat exchanger surfaces, circuiting etc. Additional improvements opportunities were found by optimizing Refrigerant Charge. SEER changed from 14.0 Btu/Wh to 16.6 Btu/Wh a gain of about 19%. We ended with a HSPF value of 10.6 Btu/Wh. As a first step, several Scroll Variable Speed Compressors models with different rated capacities and efficiencies were evaluated. Once the system model identified the best compressor candidate, we performed a validation run in the laboratory to confirm the findings of the system model before determining the other design options. Our findings show that the model provides excellent correlation between measured and simulated results. Next, we simulated several cases with different combinations of Compressor Speeds and Indoor and Outdoor Air Flow Rates for maximizing Cooling and Heating Performances. An additional benefit of the Indoor Fan Strategy is improved dehumidification with a lower Sensible Heat Ratio for cooling mode and higher delivered temperature for heating mode operation. We next performed simulations to find the best refrigerant charge for various combinations of Subcooling and Compressor Superheat settings. Once the design options were identified we proceeded to validate the simulated results with experimental data per guidelines listed in AHRI Standard 210/240 for both cooling and heating mode operation. Our findings show, the model’s accuarcy is within 5% for a variety of operating conditions. Using the simulation tool to model the system and analyze numerous design changes can eliminate several weeks of expensive laboratory testing and evaluation. While, the real cost of engineering time will vary by organization, it can safely be shown that there is a significant cost benefit associated in using the model to rapidly identify design options. It also offers opportunity to streamline the product development process and speed of the time it takes to get new products to market.