Lord Kelvin is credited with the saying "If you can not measure it, you can not improve it." To effectively measure, and ultimately improve, energy and natural resource use in a building, you must first know how much is used. To obtain the most accurate picture, a building must have meters on all the major users of energy and natural resources: electrical, gas and water.
While all buildings have at least those three meters, i.e., one for each, to develop an effective reduction plan, some use needs to be broken down into smaller increments. For instance, one electric meter cannot tell you where the electrical energy is really being used.
At the very minimum, separate electric meters should be installed for lighting, HVAC systems and plug loads. Lighting can be further separated into interior and exterior. In a large building HVAC systems should be separated into air handling equipment, chillers, cooling towers, etc., including any piece of equipment that uses a large amount of power. Plug loads are made up of all the electronic devices plugged into those receptacles in the walls. They typically use 10-20% of the electrical energy in a commercial office building. Surprise!
Only with multiple meters can the real energy over-users be identified. For example, if the energy used by a large water-cooled chiller is constantly increasing on a monthly basis, normalized for weather conditions, it might mean there is a problem with the cooling tower. The problem could be that the condenser coils are getting plugged with minerals, or it could be that the cooling coils are dirty and thus are less efficient in cooling and dehumidifying the air passing across them. With only one electric meter for the entire building, this problem would never be identified as there would not be a specific increase in energy usage that reveals this condition. These are some of the challenges we find when we perform energy audits.
Another example: Water should be separated, at a minimum, into interior and exterior use, i.e., irrigation. Further, the water used by cooling towers should also be separately metered. This way the building may be able to eliminate sewage charges, which can be a considerable percentage of the water charge.
Today’s meters are not only considerably less expensive and more versatile than they used to be, but for many applications can be wireless, which leads to lower installation costs. Measuring the usage of electricity or natural resources and comparing the numbers against what you would have expected in the various areas, as determined by a realistic energy model, is the only way to truly know what is going on in your building. The first cost of good, well-engineered metering will be returned to you many times over during the life of the building.
