COMPREHENSIVE RESEARCH FINDS ECONOMIZER PLUS
DEMAND CONTROL VENTILATION DELIVERS HIGHEST ENERGY SAVINGS
Honeywell-Funded Study Yielded Consistent Results Across 8 Control Strategies, 4 Building Types, 20 Locations

MINNEAPOLIS, AUGUST 21, 1998 — A comprehensive new study by two independent experts shows that economizers coupled with demand control ventilation is the best strategy to significantly cut energy costs across a variety of building types and climates.

The study*, funded by Honeywell, found that using a differential enthalpy economizer control with demand control ventilation can save up to 80 percent in energy bills annually in some applications.

The research further found that using a fixed minimum outside air flow strategy is the most expensive option in all applications; and that demand control ventilation alone doesn't always save energy and, in fact, in some locations actually drives up energy costs.

The evaluation is believed to be the first that directly compares the effectiveness of eight leading ventilation strategies across a broad range of building- and geography-specific applications.

"The industry has long known that economizers and demand control ventilation (DCV) can result in energy savings for commercial buildings," said Adrienne Thomle, Honeywell Home and Building Control senior product manager. "But until now, we've lacked really comprehensive, comparative studies.

"This research shows that facilities managers have the tools available to reduce utility bills without sacrificing occupant comfort," she noted. "A differential enthalpy economizer system using inputs from a carbon dioxide sensor is the most effective way to save money while assuring adequate ventilation levels, in most applications."

Research methodology

Two well-known experts in building energy analysis —Michael J. Brandemuehl, University of Colorado at Boulder, and James E. Braun, Purdue University — designed, conducted and reported preliminary findings from the evaluation. To ensure impartial findings, Honeywell did not provide input into the analysis process or the results.

Brandemuehl and Braun scientifically simulated conditions using three sets of variables. First, their simulations encompassed four different buildings: an office building, large retail store, school and sit-down restaurant. The researchers developed their models based on building descriptions and characteristics from commercial building prototypes developed by Lawrence Berkeley National Laboratory.

Second, the study simulated energy use for those buildings in 20 cities, including Boston; Miami; Madison, Wisconsin; Atlanta; Albuquerque; Denver; and Seattle.

And third, the researchers evaluated energy consumption using eight different control strategies:

Basic ventilation control. The buildings' air handling units delivered fixed minimum outside air flow to meet minimum required ventilation rates, per ASHRAE Standard 62-1989.

Basic control plus economizer options. The researchers then evaluated energy consumption using economizer controls with three different inputs: outdoor dry bulb, which measures outside temperature only; single outdoor enthalpy, which measures outside temperature and humidity, and compares those measurements to a set point representing a line on the psychometric chart; and differential enthalpy, which compares the outside temperature and humidity with the return air's measurements, then chooses the optimum cooling option.

Demand control ventilation. The researchers evaluated energy consumption using a CO2 sensor to control ventilation. Carbon dioxide is a byproduct of human respiration, and its levels in a space correlate well with occupancy levels. The study evaluated energy use with a CO2 sensor and the base strategy, and then in conjunction with each of the three economizer control options.

Summary findings

Across all 640 simulated situations, the researchers found:

1. Using a base ventilation control strategy is the most expensive option in every situation.

2. Actual building occupancy generally falls far short of the maximum expected (i.e., design) occupancy. Additionally, occupancy levels can vary dramatically, depending on building type, over the day. Yet many buildings' air handling units provide fresh-air ventilation based on design occupancy, causing significant overventilation and needlessly driving up related energy costs.

3. Economizers helped reduce energy costs in every application. The dry-bulb outdoor air strategy produced minimal savings except in the most arid locations; single and differential enthalpy strategies produced significantly greater savings.

4. In every case, a differential enthalpy economizer plus demand control ventilation saved the most in energy costs (see Figs. 1 and 2 for simulated office building electrical use in three cities). Potential energy savings in the study ranged from 30 percent to more than 80 percent depending on climate and building type.

5. Demand control ventilation, or DCV, resulted in significant energy savings in the heating mode. In the cooling mode, however, DCV alone did not save energy. In more than 50 percent of the simulations, using this strategy actually increased cooling-related energy costs.

For more information on the study, Honeywell's industry-leading economizer™ system controls and its new line of reliable CO2 sensors, call 1-800-345-6770, ext. 7502; send e-mail to info@corp.honeywell.com; or visit Honeywell's Internet site, www.honeywell.com (select the Solutions for Buildings section, then HVAC Commercial Components, and look under "What’s New").

Honeywell Home and Building Control provides products and services to create efficient, safe, comfortable environments. The business offers controls for heating, ventilation, humidification and air-conditioning equipment; security and fire alarms; home automation systems; energy-efficient lighting controls; and building management systems and services.

Honeywell is a global controls company focused on creating value through technology that enhances comfort, improves productivity, saves energy, protects the environment and increases safety. The company services customers worldwide in the home and building, industrial, and aviation and space markets. Honeywell employs 57,500 people in 95 countries, and had 1997 sales of $8 billion.

* All citations come from "Analysis of Energy Requirements for Alternative Ventilation Control Strategies" by Michael J. Brandemuehl, University of Colorado at Boulder, and James E. Braun, Purdue University, submitted to Honeywell April 13, 1998.