ASHRAE Journal - August 2012 - 38

Controls
Many of the preceding improvements must be matched with appropriate controls. A BMS centralizes monitoring and automated control of all building equipment and setpoints interfaced to the system. In some buildings, the installation of dashboard displays of real-time energy use has motivated the building engineering staff to tweak operation still further. We have observed that some operating staff manually change VSDs or change setpoints to lower peak demand based on the dashboard display. Once the controls are centrally located, further improvements to their function are possible. Anomalies in operation are quickly alarmed and observed. Moreover, building engineers can implement many simple no- or low-cost retrocommissioning procedures through the BMS such as: adjusting equipment start/stop schedules, modifying off hours/setback temperatures, selected tenant overtime operation, etc.

Pump and Chiller Energy (kW)

through the chiller is generally only possible with newer chillers. The combination of pump and chiller consumption energy is often lower at 2 gpm/ton than 3 gpm/ton (0.037 L/s·kW than 0.054 L/s·kW) (Figure 6). In some cases, varying the condenser water flow depending on cooling load may be advantageous.

750 700 3 gpm/ton CW 650 2 gpm/ton CW 600 550 500 450 400 350 300 250 200 150 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 Cooling Load

Figure 6: Pump and chiller energy use at 2 vs. 3 gpm/ton (0.037 L/s·kW vs. 0.054 L/s·kW) condenser water in a sample 1,000 ton (3517 kW) plant demonstrating reduction in total energy use with lower condenser water flow. • Other, more profitable investment opportunities. On the other hand, many corporate tenants are demanding improvements in building performance, including LEED compliance, prior to lease renewal, which is motivating property owners to invest in their assets. Also as noted, some state or municipal codes are mandating more stringent requirements. As engineers who work in the built environment, upgrading the energy efficiency of the large stock of existing buildings is perhaps our most important challenge and legacy.

Cogeneration
Generating electricity on-site and using the waste heat for heating or cooling has been an option in some office buildings. The author has designed both microturbine and reciprocating engine installations in a number of NYC office buildings. Other types of facilities with constant thermal loads, like hospitals, can be even more cost-effective. Significant incentives from NYSERDA are offered provided that emissions and the overall annual thermal efficiency exceed a minimum annual threshold. From the perspective of overall sustainability, generating electricity and using the waste heat for useful cooling or heating is much more efficient than central utility plant electricity. Usually, by the time the utility electricity reaches the consuming device, the thermal efficiency (typically gas in the NYC area) is only 30%. 7 Seventy percent is lost to the environment either at the power plant or in transmission. On the other hand, typical cogeneration plants using the waste heat effectively are at least 60% efficient on an annual basis. The most important criterion for selecting a cogeneration plant size is the availability of waste heat use.

References
1. City of New York. 2011. “Inventory of New York City Greenhouse Gas Emissions September 2011.” Jonathan Dickinson and Andrea Tenorio (ed.). N.Y.: Mayor’s Office of Long-Term Planning and Sustainability. 2. Con Edison. 2011. “Steam System.” www.coned.com/newsroom/ energysystems_steam.asp. 3. Con Edison. 2011. Personal correspondence with author. 4. Meckler, M. 2011. “The sustainable carbon neutral hybrid chiller.” Engineered Systems 28(5). 5. Rishel, J. 2010. “Save chiller plant energy with Guideline 222008.” ASHRAE Journal 52(2). 6. SPX Cooling Technologies Inc. 2010. Product Data. 7. EIA. 2011. “Annual Energy Review 2010.” Energy Information Administration. http://www.eia.gov/totalenergy/data/annual/ archive/038410.pdf. 8. NYC.gov. 2012. “Energy Aligned Clause.” www.nyc.gov/html/ gbee/html/initiatives/clause.shtml. One of the mayor’s energy conservation committees, of which this author was a part, included an initiative to remove the landlord/tenant split incentive by creating an Energy Aligned Clause benefiting both parties while reducing energy use. Property owners offset the amortized cost of a capital improvement that reduces operating expenses. 9. Taylor, S., C.H. Cheng. 2010. “Why enthalpy economizers don’t work.” ASHRAE Journal (52)11. ashrae.org August 2012

Conclusions
As much as energy saving projects might be compelling, building owners have other criteria affecting their decisions, such as: • How long they plan to own the property; • Whether provisions in the tenant leases incentivize the owner to upgrade;8 and
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ASHRAE Journal - August 2012

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