Comparative Evaluation of Infra-Red Radiant and Forced-Air Convection Heating Systems for Hog Barns

by 5m Editor
29 June 2010, at 12:00am

Compared to a room with conventional forced-air convection heating, the room with infrared radiant heating system consumed more gas but used less electrical energy and had more uniform temperature distribution within the room, according to Dr Bernardo Predicala and colleagues in the latest Centred on Swine from the Prairie Swine Research Centre. The heating system did not affect pig performance.

Bernardo Predicala

The overall goal of this study was to compare a gas-fired infra-red radiant heating system with a conventional forced-air convection heater for supplying supplemental heat to pig production rooms. Forced-convection air heaters that are widely used in commercial barns typically heat the air near the ceiling, and in turn, the heated air has to be physically moved, using fans and inlets, to the animal-occupied zones. A radiant heater transmits heat to surfaces, e.g. floor, pen wall, animals, through radiation heat transfer, thus facilitating the heating process at the pig’s level and at the same time the heated surfaces serve as a thermal reservoir that help maintain the setpoint conditions in the room. Because of this difference in mode of heat transfer, it is hypothesized that infra-red radiant heating could help reduce heating costs in pig production rooms.

Experimental Approach

The two heating systems (forced-convection versus radiant heating) were compared for energy efficiency and impact on indoor air quality and hog performance. The comparative evaluation will be conducted over three trials, two of which are already completed. The study will cover the seasonal variation in ambient environmental conditions throughout the year.

Two grow-finish rooms at PSCI research facility were used; one room had a 80,000 BTUh forced-air heater (control) while a 80,000 BTUh gas-fired infra-red radiant heater (treatment) was installed in the other room (shown in Figure 1). Both heater units were brand new when installed. Each room has inside dimensions of 66 × 24 × 10 feet and has 20 pens that could accommodate five pigs per pen, each pig averaging between 25 to 30kg starting weight. The rooms were identical in terms of building construction, pen configuration, animal capacity, and care and management.

Figure 1. Experimental rooms. A: Treatment room with a 50-ft long infrared radiant heater (inset- heater part); B: Conventional production room with a forced-air convection heater (inset).

Various monitoring instruments were set up in each room to assess the performance of the two heater types. A gas metre equipped with a pulser was installed in each room to monitor gas consumption. Energy loggers were also used to record electrical energy consumption of ventilation fans, lights, and heater blower motor. Sensors used to monitor air temperature and relative humidity, ventilation rate and gas concentrations were also deployed in the room. In addition, performance indicators for the pigs were recorded throughout each trial.

Results from Completed Trials

Gas and electrical energy consumption

The first trial was started in late spring in 2008, during which the ambient conditions became warm enough that the infrared radiant heater was needed only for the first two weeks while the forced-air heater ran intermittently only for the first three weeks. Gas consumption by the radiant heater was slightly higher in the first week but lower in the following 2 weeks than the forced-air heater.

Trial 2 was started in early winter and the gas consumption of both heaters is shown in Figure 2. It can be observed that both heaters were barely in operation after week 7, which was expected since the setpoint room temperature at this stage of growth is lower and the pigs are large enough to generate adequate heat to meet the setpoint. However, for the weeks of the trial when both heaters were operating, the infrared radiant heater consumed 98 cubic metres of gas more than the forced-air heater.

Figure 2. Gas consumption of infrared radiant heater and forced-air convection heater in trial 2

The average amount of electrical energy consumed (trial 1 and 2) in both the infra-red radiant heater and forced-air heater rooms is shown in Figure 3. Throughout the 12-week test period, electrical consumption was relatively similar in both rooms. However, total electricity use was 205kWh higher in the Control room than the Treatment room. This could be attributed to the additional electrical energy consumed by the recirculation fan in the control room. It should be noted that the recirculation fan is part of the heating and ventilation system necessary to distribute heat more uniformly throughout the control room; no recirculation fan was required for the treatment room.

Figure 3. Total electrical energy consumption in the rooms with forced-air convection heater and with infra-red radiant heater

Indoor air quality

Air quality parameters monitored within each room include air temperature, relative humidity, ventilation rate and gas concentrations.

Figure 4 shows the average temperature readings at the different locations within the Control and Treatment rooms during the first three weeks of each trial when both heaters were in operation. It can be observed that temperatures near the middle of the room were slightly higher than those at the peripheral locations of the room, especially near the exhaust fan. This slight temperature variation could be due to heat loss through the outside wall where the exhaust fans were installed.

A comparison between the first and second trials showed that temperature variation was slightly higher in the second trial; this could be due to the colder ambient temperature since the average ambient temperature during the trial was 19.2°C colder than during the first trial. Additionally, the set-point temperatures for both rooms during the first three weeks of the test period was 23.7, 22 and 20°C for the first, second and third week, respectively. The observed range of deviation above and below the setpoint temperature in all the locations in the Treatment room were 0.9 and 1.8°C respectively, while the corresponding values in the Control room were 0.4 and 1.3°C, respectively.

Figure 4. Average temperature distribution within the treatment (A) and control (B) rooms during the first three weeks of the test period

The average relative humidity readings recorded in the middle and near the exhaust fan in the forced-air heater room (59 per cent) was slightly higher than those in the radiant heater room (57 per cent). With regard to ventilation, average rates observed in the control and treatment rooms were 3269.7 and 3125.0L/s, respectively, during the first trial and 836.7 and 644.8L/s, respectively, in the second trial.

Over the course of the trials, hydrogen sulphide (H2S) and carbon monoxide (CO) concentrations in both rooms were usually at levels barely detectable by the sensors with average concentrations of less than 1 ppm for either gas. However, during pit pulling events, concentrations of H2S were observed to spike to considerably high levels with peak concentration of 91 and 97ppm in the control and treatment rooms, respectively. Ammonia and carbon dioxide levels were relatively similar in both rooms with average concentrations below 10 and 2,000 ppm, respectively.

Pig performance

The average daily gain (ADG), average daily feed intake (ADFI), and mortality rate were monitored during the two trials to evaluate the effect on hog performance.

ADG and ADFI were found to be similar in control and treatment rooms. Average ADG values from the two trials were 0.95 and 0.94kg/pig-day, while ADFI values were 2.64 and 2.55kg/pig-day for the control and treatment rooms, respectively.

Feed intake of pigs in the control room was slightly higher than in the treatment room, hence resulting to a slightly faster growth rate. During the first trial, average mortality rates of 1.8 per cent and 4.0 per cent were recorded in the control and treatment rooms, respectively, and zero mortality was recorded in both rooms during the second trial.

Based on observations during daily animal health checks, mortalities in both rooms were health related, such as incidence of lameness and infections, and were unlikely to be related to heater performance.

The Bottom Line

Observations from the two completed trials so far indicated that compared to a grow-finish room with conventional forced-air convection heater, the room with infra-red radiant heating system has consumed more gas but used less electrical energy, had a more uniform temperature distribution within the room, and had no adverse impact on the growth performance of the pigs. These observations will need to be verified after all trials are completed and appropriate statistical tests are conducted.

June 2010