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Pre and post thermal load is calculated using before-after whole-building cooling and heating sub-metered measurements.

F-1. HVAC System Types

In order to facilitate the description of measurement methods that are applicable to a wide range of HVAC systems, it is necessary to categorize HVAC systems into groups, such as single zone, steady state systems to the more complex systems such a multi-zone systems with simultaneous heating and cooling. To accomplish this two layers of classification are proposed, in the first layer, systems are classified into two categories: systems that provide heating or cooling under separate thermostatic control, and systems that provide heating and cooling under a combined control. In the second classification, systems are grouped according to: systems that provide constant heating rates, systems that provide varying heating rates, systems that provide constant cooling rates, systems that provide varying cooling rates.

• HVAC systems that provide heating or cooling at a constant rate include: single zone, 2-pipe fan coil units, ventilating and heating units, window air conditioners, evaporative cooling. Systems that provide heating or cooling at a constant rate can be measured using: single-point tests, multi-point tests, short-term monitoring techniques, or in-situ measurement combined with calibrated, simplified simulation.

• HVAC systems that provide heating or cooling at varying rates include: 2-pipe induction units, single zone with variable speed fan and/or compressors, variable speed ventilating and heating units, variable speed, and selected window air conditioners. Systems that provide heating or cooling at varying rates can be measured using: single-point tests, multi-point tests, short-term monitoring techniques, or short-term monitoring combined with calibrated, simplified simulation.

• HVAC systems that provide simultaneous heating and cooling include: multi-zone, dual duct constant volume dual duct variable volume, single duct constant volume w/reheat, single duct variable volume w/reheat, dual path systems (i.e., with main and preconditioning coils), 4-pipe fan coil units, and 4-pipe induction units. Such systems can be measured using: in-situ measurement combined with calibrated, simplified simulation.

F-2. HVAC System Testing Methods

In this section four methods are described for the in-situ performance testing of HVAC systems as shown in Table 27.14, including: a single point method that uses manufacturer's performance data, a multiple point method that includes manufacturer's performance data, a multiple point that uses short-term data and manufacturer's performance data, and a short-term calibrated simulation. Each of these methods is explained in the sections that follow.

• Method #1: Single point with manufacturer's performance data

In this method the efficiency of the HVAC system is measured with a single-point (or a series) of field measurements at steady operating conditions. On-site measurements include: the energy input to system (e.g., electricity, natural gas, hot water or steam), the thermal output of system, and the temperature of surrounding environment. The efficiency is calculated as the measured output/input. This method can be used in the following constant systems: single zone systems, 2-pipe fan coil units, ventilating and heating units, single speed window air conditioners, and evaporative coolers.

Table 27.13: Relationship of HVAC Test Methods to Type of System.

Test Method

HVAC System

Constant Heating or Cooling

Variable Heating or Cooling

Simultaneous Heating and Cooling

1. Single Point with Manufacturer's Performance Data

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