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Combined heating & cooling - Heat pump - Ground-source - Penitentiary / Canada
Case study assignment
You are an engineer with Public Works Canada who is charged to head the tendering process for the heating, ventilation and air-conditioning (HVAC) system at a new women's prison. The prison is to be built to accommodate Correctional Service Canada's Green Plan. You want the contractors to consider a ground source heat pump (GSHP) heating/cooling system but you first need to verify that this option could be financially viable.
Site information
The new facility will be located in Truro, Nova Scotia. The ground overburden material is about 16 m thick and consists of damp clay and gravel. Beneath this the sandstone and siltstone bedrock begins. According to the geotechnical study for the facility, the mean earth temperature is reported to be about 8°C with an annual amplitude of 14 °C. The facility is a "campus style" design consisting of 12 one and two story buildings that include residential units, gymnasium, recreation building, education building, office areas, health and food services and an enhanced security building. The total occupancy is intended to be 35 inmates and staff. The campus grounds cover 25,000 m².
All of the buildings have high levels of insulation and high performance windows. Security concerns led to the selection of an in-floor heating system for all buildings. While all of the buildings are heated, only about 30% of the space (the administration and staff areas) is cooled. The inmate areas and gymnasium are not cooled. The alternate conventional system being considered consists of split system air-conditioners with cooling tower and high efficiency oil-fired boilers in a central location.
The design-day and annual heating/cooling energy requirements have been determined via detailed calculations. The peak heating demand is 211 kW with annual heating energy requirements of 440 MWh. The peak cooling demand is 63 kW with an annual cooling requirement of 33 MWh.
Currently Nova Scotia is supplying 70% of its electricity generation with coal and the remaining 30% is split between natural gas, oil and small hydro.
Financial information
Eighty percent of the cost will be paid for in debt and the interest paid on the debt will be 8% over a 20-year term. The current discount rate used by Correctional Service of Canada is 8% and the inflation rate is 2%. Fuel costs are expected to rise at roughly a half-point above the inflation rate. Both the GSHP and the conventional HVAC system are expected to last 25 years.
Currently electricity costs 8.2¢/kWh. While heating oil (diesel #2 oil) prices have been volatile, they are expected to average 60¢/l. You can assume that maintenance costs will be similar for both the GSHP and the conventional systems. Heat pumps for the GSHP system are expected to cost about $330/kW (on a cooling capacity basis). For the conventional HVAC system, the cost of the split system air-conditioners with one cooling tower has been estimated at $103,000, while the high efficiency oil-fired boilers would cost about $26,300 in total. To simplify the analysis, you can assume that the cost of the cooling and heating distribution system inside the buildings (e.g. ducts and piping) will be approximately equal for both the GSHP and the conventional HVAC.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Real project
Results
The Federally Sentenced Women's Facility in Truro, Nova Scotia was constructed in 1994. A ground source heat pump (GSHP) system was installed to heat and cool the prison. The GSHP system was selected in part because the Green Plan of Correctional Service Canada encourages the department to reduce its greenhouse gas (GHG) emissions. The site has also been used as a research facility and several types of ground heat exchangers have been installed to compare their performance. Monitoring of these systems has been carried out.
System description
Three different types of ground heat exchanger have been used at the site: a "slinky" heat exchanger; a cylindrical spiral heat exchanger ("Svec spiral"); and a vertical heat exchanger loop. Since the initial project was built, two new heat pumps have been installed, along with additional ground loops. One of the new heat pumps uses propane gas as the refrigerant. In total, some 20 individual heat pumps have been installed to serve the various buildings and zones within buildings.
During the winter months the heat pumps are used to move energy from the ground to the facility's in-floor heating system. During the summer months however the heat pumps are bypassed and heat from the buildings is rejected directly to the ground.
One novel energy efficiency measure that was implemented involves rejecting the waste heat from refrigeration units in the food preparation area into the ground-source loop. This reduces the heat gain in the kitchen and delivers it to other areas of the building where it is most needed.
Lessons learned
The big picture
Greenhouse gas emission reduction projects at government facilities can serve as effective demonstration projects and lead the way for the acceptance of renewable energy technologies. Ground source heat pumps are particularly effective at reducing GHG emissions in markets where they displace heating fuels with high carbon content (e.g. oil and coal) and where electricity is generated primarily from low carbon sources (e.g. natural gas, hydro, wind).
GSHPs are based on technologically mature compression-expansion devices that are simple and easy to maintain. Their acceptance in the marketplace is expected to increase with greater awareness of their benefits. This will be helped by detailed monitoring and publication of results for high-visibility GSHP installations, as is being done at the Truro Prison Complex.
Photo
Penitentiary - Heat pump - Ground-source, Nova Scotia, Canada
References
Case study assignment
You are an engineer with Public Works Canada who is charged to head the tendering process for the heating, ventilation and air-conditioning (HVAC) system at a new women's prison. The prison is to be built to accommodate Correctional Service Canada's Green Plan. You want the contractors to consider a ground source heat pump (GSHP) heating/cooling system but you first need to verify that this option could be financially viable.
Site information
The new facility will be located in Truro, Nova Scotia. The ground overburden material is about 16 m thick and consists of damp clay and gravel. Beneath this the sandstone and siltstone bedrock begins. According to the geotechnical study for the facility, the mean earth temperature is reported to be about 8°C with an annual amplitude of 14 °C. The facility is a "campus style" design consisting of 12 one and two story buildings that include residential units, gymnasium, recreation building, education building, office areas, health and food services and an enhanced security building. The total occupancy is intended to be 35 inmates and staff. The campus grounds cover 25,000 m².
All of the buildings have high levels of insulation and high performance windows. Security concerns led to the selection of an in-floor heating system for all buildings. While all of the buildings are heated, only about 30% of the space (the administration and staff areas) is cooled. The inmate areas and gymnasium are not cooled. The alternate conventional system being considered consists of split system air-conditioners with cooling tower and high efficiency oil-fired boilers in a central location.
The design-day and annual heating/cooling energy requirements have been determined via detailed calculations. The peak heating demand is 211 kW with annual heating energy requirements of 440 MWh. The peak cooling demand is 63 kW with an annual cooling requirement of 33 MWh.
Currently Nova Scotia is supplying 70% of its electricity generation with coal and the remaining 30% is split between natural gas, oil and small hydro.
Financial information
Eighty percent of the cost will be paid for in debt and the interest paid on the debt will be 8% over a 20-year term. The current discount rate used by Correctional Service of Canada is 8% and the inflation rate is 2%. Fuel costs are expected to rise at roughly a half-point above the inflation rate. Both the GSHP and the conventional HVAC system are expected to last 25 years.
Currently electricity costs 8.2¢/kWh. While heating oil (diesel #2 oil) prices have been volatile, they are expected to average 60¢/l. You can assume that maintenance costs will be similar for both the GSHP and the conventional systems. Heat pumps for the GSHP system are expected to cost about $330/kW (on a cooling capacity basis). For the conventional HVAC system, the cost of the split system air-conditioners with one cooling tower has been estimated at $103,000, while the high efficiency oil-fired boilers would cost about $26,300 in total. To simplify the analysis, you can assume that the cost of the cooling and heating distribution system inside the buildings (e.g. ducts and piping) will be approximately equal for both the GSHP and the conventional HVAC.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- Greenhouse gas (GHG) reductions are low because it is assumed that the existing grid mix is the base case electricity system in Manitoba, where most of the electricity generation is from hydroelectric facilities. However, since the GSHP requires less energy than conventional electric resistance heating systems and air-conditioners, it increases the potential for the local utility to sell its cleaner surplus electricity to neighbouring utilities that might have more GHG emissions per unit of electricity production (e.g. coal plants in Ontario).
- No initial cost credits are available since this is a retrofit situation where the GSHP is replacing an electric heating and cooling system that does not need to be replaced.
- A tax analysis is not included because municipal facilities generally do not pay income or property taxes.
Real project
Results
The Federally Sentenced Women's Facility in Truro, Nova Scotia was constructed in 1994. A ground source heat pump (GSHP) system was installed to heat and cool the prison. The GSHP system was selected in part because the Green Plan of Correctional Service Canada encourages the department to reduce its greenhouse gas (GHG) emissions. The site has also been used as a research facility and several types of ground heat exchangers have been installed to compare their performance. Monitoring of these systems has been carried out.
System description
Three different types of ground heat exchanger have been used at the site: a "slinky" heat exchanger; a cylindrical spiral heat exchanger ("Svec spiral"); and a vertical heat exchanger loop. Since the initial project was built, two new heat pumps have been installed, along with additional ground loops. One of the new heat pumps uses propane gas as the refrigerant. In total, some 20 individual heat pumps have been installed to serve the various buildings and zones within buildings.
During the winter months the heat pumps are used to move energy from the ground to the facility's in-floor heating system. During the summer months however the heat pumps are bypassed and heat from the buildings is rejected directly to the ground.
One novel energy efficiency measure that was implemented involves rejecting the waste heat from refrigeration units in the food preparation area into the ground-source loop. This reduces the heat gain in the kitchen and delivers it to other areas of the building where it is most needed.
Lessons learned
- Maintenance costs for GSHP systems are comparable to those of conventional HVAC systems but special training for personnel is required. This facility experienced some start-up problems and has since implemented a comprehensive preventative maintenance program.
- After the initial difficulties, the system has operated reliably.
- The client is satisfied with the ground source heat pump system. Compared to conventional oil-fired heating, the GSHP provided similar greenhouse gas emission reductions as another alternative that was considered: a high-efficiency propane-fired heating system. The GSHP however had much lower operating costs than the propane system.
The big picture
Greenhouse gas emission reduction projects at government facilities can serve as effective demonstration projects and lead the way for the acceptance of renewable energy technologies. Ground source heat pumps are particularly effective at reducing GHG emissions in markets where they displace heating fuels with high carbon content (e.g. oil and coal) and where electricity is generated primarily from low carbon sources (e.g. natural gas, hydro, wind).
GSHPs are based on technologically mature compression-expansion devices that are simple and easy to maintain. Their acceptance in the marketplace is expected to increase with greater awareness of their benefits. This will be helped by detailed monitoring and publication of results for high-visibility GSHP installations, as is being done at the Truro Prison Complex.
Photo
Penitentiary - Heat pump - Ground-source, Nova Scotia, Canada
References
- Green, Troy, "Personal communication," Earth Energy Utility, 2002.
- Kemp, Steve, "Personal communication," Enermodal Engineering Ltd., 2002.
- Natural Resources Canada, Federally Sentenced Women's Facility, Ottawa, Canada, 1999.
- O'Blenes, Brian, "Personal communication," Correctional Service Canada - Atlantic Region, 2002.
