1222 The EMCS Retrofit

Without the benefit of a DDC EMCS the operator of the example building must incur after-normal hours operating costs and allocate them over the entire leasing cost. This unfairly spreads the costs generated by a few tenants over the lease costs of all tenants. The overall effect are higher leasing charges for all.

The most cost effective way to retrofit a DDC EMCS in a building controlled by a reasonably maintained pneumatic control system is to interface it with the existing pneumatics in a supervisory mode by eliminating night thermostats, replacing time clock contacts with DDC outputs, direct hard wiring for start/stop control of the equipment not under the influence of the pneumatic system (i.e. toilet exhaust fans, domestic service hot water circulators, and corridor, lobby and exterior lighting); direct hard wiring boilers, chillers and hot water and chilled water circulators for start/ stop control, and direct hard wiring to enable/disable the equipment under control of the pneumatic system (i.e. the AHUs and dampers). Enabled equipment is allowed to operate under the control of the pneumatic system. Disabled equipment is shut down (Figure 12.2).

With a supervisory DDC system the building operator can effect a dramatic reduction in energy usage by incorporating a simple timed on/off control strategy for all HVAC and lighting zones that segregates the operation of the equipment into discrete tenant zones. The control strategy would shut down the tenant zones when outside of normal lease times. If a tenant wished to utilize a space after hours, he/she could initial an override (using a simple automated telephone interface from his/her office) to signal the system to preserve his/her working environment. Additionally, on weekends and holidays the entire building can be kept in the unoccupied mode unless a tenant requires extended occupancy of a particular zone. That tenant could initiate an override from any outside telephone to ensure occupied conditions for his/her space upon arrival at the building. Whenever an override is initiated, an operator interface level personal computer could track the energy consumption and/or runtimes of that zone's HVAC equipment for the purpose of billing the tenant an after hours usage charge.

Experience at a multiple tenant, high rise commercial office building on Long Island, New York, has shown that this "tenant strategy" not only results in a dramatic reduction in energy usage but also allows the building operator to reduce the base rental and recover after normal hours operating cost directly from those tenants responsible for the use.

By installing a DDC system as a supervisor of and existing pneumatic control system the building operator

AI-1 Boiler #1 water supply temperature

AI-2 Boiler #2 water supply temperature

AI-3 Common boiler water supply temperature

AI-4 North loop supply temperature

AI-5 South loop supply temperature

AI-6 North loop return temperature

AI-7 South loop return temperature

AI-8 Outside air temperature sensor

AI-9 Ambient light sensor

BI-1 Circ Pump #1 flow

BI-2 Circ Pump #2 flow BI-3 Circ Pump #3 flow BI-4 Circ Pump #4 flow

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