ASHRAE Journal - August 2012 - 33

buildings. Payback years are esMeasured Standard 62.1-2007 Test Percent Outside Air vs. Excess Air timated averages from audited Outside Air Outside Air Requirement (cfm) Building ASHRAE Required* (cfm) (cfm) building stock. Typically, build1 145,040 694,448 479% 549,408 ing managers and owners can only regulate the energy used by 2 94,120 210,978 224% 116,858 the base building. Tenant use is 3 234,040 282,026 119% 47,986 generally not under management 4 49,452 72,986 148% 23,534 control. 5 97,800 177,017 181% 79,217 In many cases, summer comfort 6 124,599 163,266 131% 38,667 cooling uses a significant share of * Dampers open to minimum position. the energy consumed. One of our key findings is that many NYC Table 4: Excess outside air is common in these large, commercial vintage buildings. buildings are overventilated, resulting in cooling of warm excess outBase Building Tenant side air. 51% 45%

Air-Handling Systems Excess Outside Air
During an early demand controlled ventilation (DCV) multiyear study in one major office building (see Test Building 1 in Table 4), we discovered that the CO2 level seldom varied much above the outdoor level of roughly 450 ppm. When the outside air quantities were eventually field tested, it was apparent that leaking dampers allowed significant amounts of excess outside air to be introduced into the building. Moreover, upon further testing, even with ostensibly closed dampers the leakage rate exceeded 40%, which results in more outside air than suggested by the ASHRAE Standard 62.1-2007; sometimes, several times more. Testing in subsequent buildings confirmed that a large majority of older commercial office buildings are overventilated, resulting in wasted energy, some for heating, but mostly for cooling (Figure 1). Understandably, many of these dampers date from the original construction of the building. Table 4 shows the results of air testing of several properties. If a majority of Manhattan office buildings have excess outside air quantities similar to Table 4, installing new dampers would significantly reduce CO2 emissions, as well as overall energy costs. Clearly, unless new tight-closing dampers are installed in these overventilated buildings, DCV will not be fully effective. Using Test Building 1 as an example, Figure 2 shows the
August 2012

Fans and Pumps 20%

16% Lighting 23% 84%

Cooling 12% Heating 11%

Plug Loads 13% Data Centers 8%

Elevators 4%

Overhead Losses 4%

Other 4%

Domestic Hot Water 1%

Incremental Savings of Implementing DCV After New Dampers Savings with New Low-Leakage Dampers

Figure 1: Typical commercial office building end use. extent to which installing low-leakage dampers can be crucial to effective use of DCV. Unfortunately, some dampers constructed by local shops have not been engineered adequately to minimize excessive outside air. The linkages and damper motors do not properly close the large damper assemblies (often 10 ft [3 m] high and as much as 20 ft [6 m] wide) and the damper blades become misaligned. Outside air dampers must be installed on a modular basis, with appropriate damper motors and linkages, to provide adequate torque to close the dampers leaktight. Only when good dampers are installed can DCV become effective. In many of these vintage buildings, even with relatively tight-closed dampers on the interior air systems, we rarely see interior air CO2 levels exceed 600 or 800 ppm, well below the 1,100 ppm

Figure 2: Test Building 1 proportional outside air savings; low-leakage dampers vs. demand controlled ventilation (DCV). (400 outside + 700) recommended by ASHRAE Standard 62.1-2007 for indoor air quality. This is in part due to the perimeter induction air systems, which are generally fixed at 50% to 60% outside air (in some cases, 100%), which contribute significant amounts of fresh air to the system.

Variable Speed Drives
Installing variable speed drives (VSDs) on the fan motors and upgrading to premium efficiency motors permits staff to reduce fan speed during the shoulder seasons by as much as 15% without adversely affecting occupant comfort. During periods of peak cooling or heating demand, the fan may require 100% airflow. Encouraging owners to implement variable air volume (VAV) interior systems in these older buildings will save the most energy. Many tenants
ASHRAE Journal 33

ASHRAE Journal - August 2012

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