Sub-metering is gaining momentum in residential, commercial, and industrial building applications.

The move to Green, eco-friendly construction and business operation has provided a catalyst for savings programs on everything from water to power. Consider that every increase in the cost of a barrel of oil magnifies the importance of conserving energy. Savings can't be accomplished without first tracking the use and potential wasting of electricity.

More than ever sub-metering is being applied in industrial as well as the traditional commercial and residential applications to encourage conservation and increase productivity. This article describes what sub-metering is, why it's important, and how to effectively apply it.

Typically, sub-metering is installed by and for the owner and is not in any way related to the utility company providing the electrical service. An industrial, or commercial/residential multi-tenant building owner installs the sub-metering equipment for the sole purpose of metering distributed power within. Thi9s is done to either allocate costs, or for internal billing purposes. In tenant billing applications, sub-metering guidelines governing usage and installation can be obtained from either the local Public Utility Commissions (PUC) or the local utility.

Although sub-metering can also be used to perform most critical functions, such as equipment monitoring, trending, alarming, some maintenance, communication, and power quality analysis, the cash savings will come primarily from monitoring energy consumption.

Since the utility provides electrical service to a building or facility, they install their own electrical meter to measure the Kwh and, in many cases, the electrical demand. These installations are referred to as either master- metered or direct-metered. They should not be confused with sub-metering.

1. By installing a Master meter, the utility provides a single metering point at the electric service entrance for the purpose of metering all electrical usage within the building. This is common for industrial and many commercial buildings where a single business entity exists. It is also common in multiple tenant buildings such as high-rise commercial or residential structures where the building owner is billed for the entire buildings energy usage. The owner or building manager must then, however, rely on some technological means to determine each tenant's actual usage. This allocation is accomplished by either sub-metering or approximation.

2. By installing individual electrical meters for each tenant in the building, the utility can Direct Meter to accurately read and bill each tenant with the correct energy information based on actual usage. This method has become common practice in multiple tenant applications and has both advantages and disadvantages over master metering.

Sub-metering has been in use for many years to measure water and gas consumption. Generally, building owners in urban areas provide all utility services to their tenants including electricity, water, and gas. Many building owners saw the advantages of combining a single utility service for the entire facility with a privately owned sub-metering system for allocating actual electrical usage to the tenants.

Many cost savings were realized in new construction by simply billing the building owner for total energy usage. Thus, the "master-metered" concept was born. The utilities provide one main meter for the building for each utility feed and the building owner would try to allocate the proper cost to each tenant. Although far from accurate, this concept stood the test of time because utilities in the past were relatively inexpensive.

The RUB (Ratio Utility Billing) method can be based on the number of tenants, square footage of the leased space, number of people, or a combination of all these factors. While RUB is logical and a master meter is inexpensive to install, the method is never accurate for allocating power costs. Tenant lifestyles might be totally different. One apartment with three tenants might consume less electricity than a similar apartment with one tenant. If everyone is sharing the bill, who cares if we turn up the air conditioning or leave the windows open and the heat on? It all gets averaged out among all the tenants. Not much help for going Green or conserving greenback dollars.

Sub-metering can determine actual energy usage of leased commercial tenant space as a basis for energy billing or cost recovery. In commercial space, energy costs are typically included as part of the lease if they are not direct metered by the utility. Sub-metering can be very useful in assigning actual energy costs to each tenant. Applications of sub-metering may also be found in any master metered multiple tenant buildings and are very useful in determining common area energy costs such as lighting, parking lot lighting and HVAC (heating and air conditioning).

Sub-metering potential benefits in residences come from knowing which areas of the home are using what portion of the total electric bill. The use of power by family members can also be monitored and adjusted. Finally, problem areas of insulation and air leaks can sometimes be discovered by variations in zoned power usage within a home.