Energy efficiency measures - Commercial - Model National Energy Code for Buildings (MNECB)
The existing MNECB is a prescriptive standard for medium sized buildings that is presently in the process of revision. The current MNECB's envelope minimum requirements are tied to the regional costs of energy. It will remain in effect until 2012, by which time a new code should be ready to replace it. In the existing code there are six major building categories with one, two or three sub-types in each group. The categories (with examples in brackets) are:
Template assignment
A 9,300 m² three story office building is located in¨London, Ontario, Canada. The building volume is 27,900 m³ and the exposed perimeter is 300 m. The HVAC system consists of an under floor air distribution system that is supplied by three air handlers, one per floor. These air handling units (AHUs) are equipped with natural gas fired burners for heating incoming air and condensers for cooling the air. Perimeter space heating uses a gas fired boiler.
Electrical equipment in the building includes lighting, pumps, fans and plug loads. There are two main pumps located in the building, for a total of 6 hp. Each air handler has a supply and exhaust fan. Total fan power for the building is 185 hp, although the fans are variable speed and do not operate at full capacity. All electrical equipment has impact on the heating and cooling load.
Base case
Fuels and schedules
Proposed case
Heating system
Building envelope
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.
The existing MNECB is a prescriptive standard for medium sized buildings that is presently in the process of revision. The current MNECB's envelope minimum requirements are tied to the regional costs of energy. It will remain in effect until 2012, by which time a new code should be ready to replace it. In the existing code there are six major building categories with one, two or three sub-types in each group. The categories (with examples in brackets) are:
- Commercial (boutiques through supermarkets)
- Business (banks, offices, clinics, rental shops, hair dressers, etc)
- Buildings for meetings (theatres, cinemas, auditoriums, schools, churches, libraries, museums, etc.)
- Health and detention centres (hospitals, prisons, orphanages, rest homes)
- Industrial buildings (divided into low, medium and high risk industries)
- Habitation (apartments, college residences, dormitories, hotels, motels, multiunit housing)
Template assignment
A 9,300 m² three story office building is located in¨London, Ontario, Canada. The building volume is 27,900 m³ and the exposed perimeter is 300 m. The HVAC system consists of an under floor air distribution system that is supplied by three air handlers, one per floor. These air handling units (AHUs) are equipped with natural gas fired burners for heating incoming air and condensers for cooling the air. Perimeter space heating uses a gas fired boiler.
Electrical equipment in the building includes lighting, pumps, fans and plug loads. There are two main pumps located in the building, for a total of 6 hp. Each air handler has a supply and exhaust fan. Total fan power for the building is 185 hp, although the fans are variable speed and do not operate at full capacity. All electrical equipment has impact on the heating and cooling load.
Base case
Fuels and schedules
- The building is occupied 9 h/d during the week and is closed on weekends
- Temperature settings are the same as MNECB defaults, 21.1 ºC for space heating, and 23.3 ºC for space cooling, temperature is allowed to vary by 3 ºC during unoccupied periods
- Heating/cooling changeover temperature is 16 ºC
- Electricity rate is $0.106/kWh, natural gas rate is $0.38/m³
- Perimeter heating is provided by a natural gas fired boiler, seasonal efficiency 80%
- AHUs have seasonal heating efficiency of 75% and are used only for conditioning ventilation air
- The hot water heating system is an instantaneous electric boiler
- Cooling is provided by condensers on each of the AHUs, condensers each have a COP of 2.5
- North side of the building faces due north
- Wall areas are: north and south 920 m², east and west 500 m²
- Walls are insulated to 1.82 m²-ºC/W
- Roof insulated to 2.4 m²-ºC/W
- Below grade floor is not insulated on-grade
- The overall window-to-wall ratio is approximately 67%
- Windows are fixed double glazed, wood frame with aluminum spacers
- Solar shading on all windows is 15% during the winter. During the summer it is 15% on the north, 20% on the east and west and 40% on the south
- Natural air infiltration is approximately 0.2 air changes per hour
- Ventilation system operates 15 hours per work day with 10% fresh air and no heat recovery
- AHUs 1 and 2 have air flow rates of 13,000 L/s, AHU 3 has air flow rate of 18,000 L/s, all with reheat coils in the system
- Lighting power density is 18 W/m², lights on when building occupied
- Electrical equipment plug loads are 7.5 W/m² when building occupied
- Instantaneous water heaters provide hot water for the 470 office occupants during business hours. Hot water temperature is 60 ºC
- The perimeter heating fluid is constantly circulated using two pumps with 3 hp standard efficiency motors and load factors of 90%. The pumps operate at constant flow with an efficiency of 60% as per MNECB
- The fans for the AHUs have the following specifications. The motors for the base case fans are variable speed, which allows them to operate at very low load factors.
- AHU 1 and 2 - supply air: 40 hp standard efficiency motor, load factor 20%, forward curved fan, 60% efficiency, variable flow, variable speed, running 15 hours per work day
- AHU 1 and 2 - exhaust air: 15 hp standard efficiency motor, load factor 20%, forward curved fan, 60% efficiency, variable flow, variable speed, running 15 hours per work day
- AHU 3 - supply air: 50 hp standard efficiency motor, load factor 20%, forward curved fan, 60% efficiency, variable flow, variable speed, running 15 hours per work day
- AHU 3 - exhaust air: 25 hp standard efficiency motor, load factor 20%, forward curved fan, 60% efficiency, variable flow, variable speed, running 15 hours per work day
Proposed case
Heating system
- Boiler to be replaced by a modulating boiler, effective seasonal efficiency 88%, at an incremental cost of $10,000
- Air handling unit burners replaced with 85% efficient burners at an incremental cost of $2,000 each
- More effective condensers installed in the air handling units, COP of 2.8, at a cost of $3,000 each
Building envelope
- Windows to be replaced with low-e, double glazed, argon filled units. Frames are thermally broken with insulating spacers
- Walls and roof insulation to be increased to 2.11 m²-ºC/W and 4.3 m²-ºC/W respectively. Assume labour costs equal materials costs
- Floor insulated on-grade with horizontal rigid insulation under the perimeter for a cost of $9,000
- Building infiltration is to be decreased to 0.1 air changes per hour for additional cost of $10,000
- In the ventilation system there will be two differences from the base case:
- First, the ventilation system will be controlled to come on one hour before start of work and remain on for an hour after work
- Second, rotary wheel heat exchangers will be installed in each air handling system for heat recovery, assume 70% efficiency
- Installation of energy efficient lighting will reduce lighting load to 9 W/m² and occupancy sensors are expected to reduce operating hours by 10%. Additional cost for lights and sensors is $6,000. Annual savings for light replacement is expected to be $500
- MNECB modeling guidelines state that the proposed and reference building must have identical electrical equipment plug loads. For an office building these loads are 7.5 W/m² and operating hours are the occupancy schedule
- The perimeter heating system pumps will be replaced with energy efficient, variable speed motor-pump sets with pump efficiency of 75% at $500 per pump
- For the fans in the AHUs, the motors in the proposed case are variable speed, which allows them to operate at very low load factors. The proposed fans for the AHUs have the same specifications as the base case except that all motors are to be replaced with energy efficient motors and all fans will be replaced by 70% efficient fans. Fans operate on the proposed ventilation schedule. Incremental cost for each fan-motor upgrade is approximately $20 per motor hp
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.
