IPC Systems Ltd. - APPLICATION
HVAC Energy Efficiency Testing
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 70oF can feel just as comfortable as a facility with a lower
temperature but higher humidity.
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
Of all the systems he evaluated, only the IOtech LogBook/360 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 LogView. 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 days
data. Some sites use an analogue 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
LogBook supplies 5 VDC power directly to the switch contacts to provide its own signal
without ancillary signal conditioning.
The LogBooks are permanently installed in the vertical back plane of an electrical
enclosure, and the sensors connect to the terminal blocks on the LogBook through
DBK15 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 wheels 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
LogView 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 LogBook has
not required calibration since its initial calibration at the factory.
HVAC manufacturers are required to meet both locally and federally regulated efficiency
ratings relative to energy conservation. In order to comply with the rules, many systems
are tested in a lab environment under procedures that let engineers collect data for
calculating the energy efficiency. One lab depends on IOtech LogBook/360 data
acquisition systems to measure temperatures to better than one degree F, as well as
relative humidity, airflow, speed or rpm, and compressor pressure. The system is
remotely located and connects to modems that download one days data to the companys main computer during low-usage times.
For sales and technical information contact:-
IPC Systems Ltd.
Tel: +44(0) 1905 338989
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