Application Summary
Manufacturers of heating, ventilating, air conditioning, and refrigeration appliances are under intense pressure, now more than ever before, to design and produce the most energy efficient equipment that they can. Often, potential customers, particularly US government facilities that must meet the Energy Policy Act of 1992, demand that the manufacturer have proof or evidence from qualified testing labs that the equipment does indeed meet the advertised or claimed efficiency ratings. One such widely used testing lab has been characterizing appliances and HVAC equipment for many years and has an impeccable reputation for its work.

The lab currently instruments such appliances to measure and collect data on a variety of electrical signals, input power, relative humidity, temperature, pressure, gas volume, and airflow — variables that are used to compute the energy efficiency. Major measurement issues hinge around the prevailing outdoor air temperature and humidity as well as the indoor values. Often, reducing the temperature of a large facility to improve comfort without considering the humidity can consume more electrical energy than dropping the humidity while ignoring the higher temperature. For example, reducing humidity to 25% at a temperature of 70°F can feel just as comfortable as a facility with a lower temperature but higher humidity.

Potential Solution
The data acquisition system intended to monitor these variables must be able to resolve a temperature measurement to better than one degree and contain sufficient input channels to accurately map the entire temperature and humidity space. A supervisor recently purchased equipment for his test lab that had no previous data acquisition equipment. He evaluated several systems, all based on a personal computer for measurement and control, but decided he needed equipment that could be left unattended, remotely located, and connected to a modem to download data to a company computer at regular intervals. Moreover, two additional critical factors were its price-to-performance ratio and construction. It had to be rugged enough to withstand some vibration and wide temperature variations.

IOtech's Solution
Of all the systems he evaluated, only the IOtech system was able to meet every requirement. The LogBook was a perfect fit because it uses an internal memory card and does not depend on the media of a separate PC to store data. As a result, the supervisor purchased five systems; four are currently in service and the fifth is a spare. Another feature he likes is . The bundled software is easy to program and communicate with through a modem from the central office. Each evening, about midnight, the office computer interrogates the various bases and downloads the day's data. Some sites use an analog instrument, such as a utility meter, that feeds pulses to the LogBook. The moving contacts of a switch generate the pulses that correspond to some known quantity such as one cubic foot of gas or one kW of electrical power. The supplies 5 VDC power directly to the switch contacts to provide its own signal without ancillary signal conditioning.

The are permanently installed in the vertical back plane of an electrical enclosure, and the sensors connect to the terminal blocks on the LogBook through signal conditioners. Each collection site measures between 18 and 20 channels of analog input, two to four counters, 24 VDC, and 4 to 20 mA loops. The 24 VDC power supply feeds up to 16 instrumentation loops and simultaneously powers the LogBook. The sensors measure dry bulb temperature and relative humidity from numerous points in systems under test. For example, airflow sensors, relative humidity sensors, and temperature sensors are placed in groups to measure outdoor air temperature, supply air temperature and flow, and a desiccant wheel's input and output relative humidity. Air passes through the slowly revolving desiccant wheel containing silica gel to remove the moisture regardless of the air temperature, a method that is more efficient than controlling just the air temperature in both small and large auditorium-size facilities.

In addition to the simplified hardware connections, the lab supervisor found the software package straightforward and easy to use. Within about only two days, he was able to set up the system and begin acquiring data. And the has not required calibration since its initial calibration at the factory.