Comparative Evaluation of Use of Heat Exchanger, Ground Source Heat Pump and Conventional Heating Systems in Grow-Finish Rooms
Initial results reveal that a heat recovery ventilator with a forced-convection heater and the ground source heat pump system reduced energy consumption for heating by 52 per cent and for ventilation by 39 per cent compared to a conventional forced-convection heater, according to Leila Dominguez, Bernardo Predicala and Alvin Alvarado of the Prairie Swine Centre in the Centre's latest newsletter.
Energy cost is one component of swine production cost that can be further reduced by using energy as efficiently as possible, particularly for many barns currently in use that have not been optimized due to low cost of energy in the past. Results from our previous work showed that space heating is an area where energy reduction can be achieved (PSC Annual Report 2008, pp. 19-20). Thus, the performance of different heating systems: a heat recovery ventilator with a forced-convection heater, a ground source heat pump, and a stand-alone forced-convection heater, in terms of energy consumption and animal productivity was evaluated in this study.
The three heating systems were installed in three 120-head grow-finish rooms at PSC barn facility. Room assignment was as follows: the room heated with the stand-alone-forced convection heater was the Control room, the one heated with the heat recovery ventilator was the HRV room and one heated with the ground source system was the GSHP room. The rooms had similar building construction, pen configuration and pig capacity. For each grow-finish cycle, a total of 360 pigs were distributed equally to the three rooms. Metering equipment were installed to monitor the electric consumption of the heat pump, heaters, lights, ventilation and recirculation fans, as well as the natural gas consumption of the forced-convection heaters in the heat exchanger and control rooms.
The heat exchanger installed was a 1500-cfm aluminum core heat recovery ventilator (Figure 1), which recovers the heat energy from exhaust air stream by heat transfer to the incoming fresh air stream.
The ground source heating system, alternatively known as geothermal heat pump, geoexchange, earth-coupled or earth-energy system was composed of a heat pump and 1,800 feet of ¾-inch diameter polyethylene pipes buried in 8.5-to 10-feet deep trenches in the ground beside the PSC barn (Figure 2). The buried pipes contained 20 per cent methanol–80 per cent water solution for absorbing heat from the ground for heating and for using the ground as heat sink when cooling is needed.
Data collection from two grow-finish cycles was conducted from October to December 2010 and January to March 2011. The mild weather conditions during the first cycle did not necessitate the use of heating. For the second cycle, energy consumption for heating and ventilation of each of the three rooms are presented in Figure 3. The energy consumption for heating included both the electrical and heating fuel consumption of the heat pump and heaters while that for ventilation included the electrical consumption for both ventilation and recirculation fans. The energy consumption data were all converted to gigajoules (GJ) to provide a better comparison of the systems.
Among the three heating systems, the heat exchanger required the least energy for heating but had the highest consumption for ventilation. The heating requirement was reduced as the heat exchanger pre-heated the incoming cold air with heat from the warm exhaust air. In terms of function, the heat exchanger basically replaced the stage 1 fan and because its power rating was higher than that of a regular stage 1 fan, the energy requirement for ventilation for the room was increased. Nevertheless, the use of heat exchanger led to 52 per cent less total energy used for heating and ventilation compared to the conventional room with forced-convection heater.
The GSHP required less energy to extract heat from the ground and heat the room air compared to the conventional heater. The use of the GSHP system led to 39 per cent reduction in total energy needed for heating and ventilation compared to the control room.
Pig performance in all three rooms was similar, as shown in Table 1, although feed intake tended to be lower in the rooms with GSHP and heat exchanger compared to the conventional room.
| Table 1. Average daily gain (kg/day) and feed intake (kg/day-pig) in the three rooms for the January to March 2011 cycle. | ||
| Room | Average daily gain (ADG) (kg/day)* |
Average daily feed intake (ADFI) |
|---|---|---|
| (kg/day-pig) | ||
| Ground source heat pump | 0.99 | 2.48 |
| Heat exchanger | 0.97 | 2.37 |
| Control | 0.99 | 2.55 |
| * BW start 20 kg, BW end 120 kg | ||
The Bottom Line
The use of the heat recovery ventilator with a forced-convection heater and the ground source heat pump system resulted in 52 per cent to 39 per cent reduction in energy consumption for heating and ventilation, respectively, relative to the conventional forced-convection heater after one heating season. However, data collection from multiple heating and cooling seasons is still needed to be able to fully compare the performance and feasibility of these three systems. Reduced energy costs will translate to reduced production cost and will help improve the profitability or minimize losses in swine operations.
Acknowledgement
Project funding provided by Advancing Canadian Agriculture and Agri-Food Saskatchewan and Saskatchewan Agriculture Development Fund.
Strategic funding provided by Sask Pork, Alberta Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund.
December 2011
