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Heating Controls
Heating Controls
In most instances, parking garages are heated with hydronic unit heaters fed from a centralized boiler system. The heaters operate from a wall-mounted thermostat which is often tampered with, resulting in wasted fan energy and heat. These systems usually have a dedicated circulation pump that operates all winter long, regardless if there is any call for heat in the garage.
Built Climate offers a packaged control solution which resolves these issues. A central controller replaces the thermostats. Remote space temperature sensors are installed in the garage as needed. The control panel reads the temperature in the garage, when a zone calls for heat, the corresponding unit heaters begin to operate.
When no zone calls for heat, the circulator pumps are shut off. The system is entirely disabled when the outdoor temperature is above set point (2 C). When the outdoor temperature is above this threshold, there is no need to operate any heaters in the garage as there is no risk of pipes freezing.
Energy savings are derived from these areas:
Energy savings are derived from these areas:
- Pump electrical energy- pumps are not operational when the outdoor temperature is above threshold.
- Fan electrical energy - electric fan motors on on the unit heaters operate less often.
- Heat loss from pipes- pumps are not circulating hot water when they are shut off and heat loss through the pipes is reduced when no heat is needed.
- Heat loss from the garage - the amount of heating hours is reduced resulting in less heat loss from the garage to the environment.
CASE STUDY
CASE STUDY
High rise building in Toronto with 300 parking spaces, 72,000 FT2 on 2 floors.
4.5 kw hot water circulation pump.
10 hydronic unit heaters with 0.52 kw fan motors.
The boilers are started for the season from September 15 to June 1st, total of 6120 hours.
The garage is maintained at a constant 10 C.
Total of 2,240’ of insulated pipe with an inner surface temperature of 160 F.
Originally, the pumps operate continuously during the heating season. With the controls implement the pumps only operate when the outdoor temperature is below 2 C (36 F). During this time, the pumps will only operate 47% of the time since this is the average call for heat demand. This equates to 22,363 kw-hrs saved per year.
In the base case, the fan motors cycle with an average heat demand of 32% in order to maintain the garage temperature at 10 C throughout the heating season. With the new controls implemented, the fans only operate when outdoor temperature is below 2 C and during this time they will cycle 47% of the time. This saves 2,131 kw-hrs per year.
Heat loss through the pipes is eliminated when the pumps are no longer circulating hot water. Assuming 2,240’ of insulated 2” pipe results in annual savings of 181,640,190 Btu’s.
Lastly, the demand for heat in the garage is eliminated when the outdoor temperature is 2 C or higher. This results in heat transfer savings when the outdoor air is between 2 and 10 C. Heat transfer through the 36,000 ft2 roof deck covered with 3’ of soil results in 83,325,243 BTU’s saved per year
Total Electrical savings: 24,495 kw-hrs or $3.674
Total Gas savings: 8,756 m3 or $2,627
A total annual savings of $6,301!
Assumptions
- Cost of natural gas at $0.30 / m3
- Cost of electricity at $0.15 / kw-hr
- and ambient temperature of 50 F or 16.23 BTU/HR per foot of pipe
- The design heating condition for the garage is -20 C (-4 F), during this time the heater fans operate at 100%. As the outdoor ambient approaches the set point (10 C), the fans cycle with an average weighted run time of 32% when the ambient is below 10 C or 47% of the time when the ambient is below 2 C.
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