In order to access the energy savings it is necessary to estimate, in the absence of accurate data, the break down of energy usage between production/process, miscellaneous loads and the environmental services.
Once the environmental load has been broken down in terms of electrical energy and prime fuel, such as gas or oil, it is necessary to further break down the electrical load to isolate the lighting load from it. Having arrived at this breakdown it is possible to apply the energy savings where each of the following BEMS techniques is used.
Centralized set point adjustment
Most areas tend to be overheated or overcooled. Say trimming the temperature set points by 1 deg F, produces a saving of approx. 10% of the energy supplied to meet these steady state heat losses or gains. It applies also to humidity control.
Time and calendar scheduling
- Anticipated savings 0.5%-20% (Htg. energy) depending on whether time override switches are fitted and how accurate they are etc.
- NB: Assume current controls do not shut valves on a Facility shutdown.
Time temperature profiling (set back etc)
- If usable, anticipated savings 3%-20%, Optimum start-stop, greater savings expected on heated areas.
- Anticipated range after time-scheduling has been taken into account is 5%-15% (heating & electrical energy).
Load cycling
- Applies to heating and ventilating and air conditioning but not heating only.
- Anticipate range 3%-10% if it can be applied. NB: significant savings possible if this technique can be applied
Supply air reset
- Applies to heating and ventilating and air conditioning but not heating only.
- Anticipated range 2%-5%.
- Savings taken into account with centralized SP adjustment.
Supply water reset
- Anticipated range 1%-3%.
Supply air pressure reset
- Applies to VAV air conditioning system.
- Anticipated range 3%-12%.
Mixing damper temperature switch over
- Applies only to recirculation. Air systems.
- Anticipated range 1%-4%.
Mixing damper economy enthalpy switch over
- Applies only to air conditioning system.
- Anticipated range 1%-2%.
Zero energy bands
- Applies only to air conditioning system.
- Anticipated range 1%-2%.
Summer reset
- Applies only to air conditioning system.
- Anticipated range 1%-2%.
Air quality
- Control of fresh air content
- Varies greatly depending on type of building.
- Anticipated range 1%-5%.
Chiller optimization
- Applies only to air conditioning system or more strictly to the chillers which supply it.
- Anticipated range 2%-7%.
Demand limiting (maximum demand control)
- A cost savings and an energy savings.
- Amount will depend on present demand charges.
Boiler sequencing
- Applies only to heating system.
- Anticipated range 1%-3%.
Lighting controls
- There are huge potential savings to be obtained on control of lighting. These range from going the whole way and using occupancy detection and the use of interior/exterior lux level sensors to vary the degree of lighting, to just using an output with manual override.
Labor Savings
- Savings in maintenance labor costs would be brought about by the more efficient use of personnel.
- While experience suggests that this does not generally mean reductions in head count, as most present day companies run with minimum staffing levels, the use of the BEMS will allow remote Facility operation, alarm monitoring (including environmental checks), Facility optimization (tuning) & fault diagnosis. It is not unreasonable to estimate that on a large site, savings in the order of 2 – 3 labor days per week can be easily achieved.
Management Information
- A BEMS can provide easily obtainable information on individual Facility performance. It has to be said that in order to make best use of an installed BEMS system some consideration may need to be given to extending the level of primary services monitoring (Gas, Elec., Steam, LPHW etc.) on a Facility by Facility basis. In general it has to be said that the management facilities afforded by the BEMS do not provide direct payback in themselves but do allow informed decisions to be made on future Facility investments and operational practices.
Miscellaneous Benefits
- Reduced Equipment Costs – For instance a motor with an estimated life of 20,000 operating hours should last 5.5 years if used 10 hours per day. If its average running time can be reduced to 7.5 hours per day its life should be extended to 7.3 years. Additionally, an item of a Facility which is monitored on an exact hours run basis rather than a speculative figure, could be periodically maintained at the correct interval either through a Planned Maintenance package or otherwise. Such situations may also be pro-active as well as re-active, allowing optimum Facility usage and maintenance personnel’s time.
- Reduced Facility Depreciation costs – While more applicable to new buildings, it is worth noting that if an installed Facility has an initial value of say $2.2m and its life is extended from 10 to 11 years the annual straight line depreciation is reduced from $220,000 per annum to $200,000 per annum.
Intangible Benefits
In addition to the tangible benefits highlighted above there are less tangible benefits which should also be taken into account. These include:
- Improved efficiency of those working in the building due to improved environmental conditions.
- The reduction in down time of a Facility and the possible reduction in frequency of failures of services which cause occupants dissatisfaction and disturbance.