Retrofit Terminal Units

Application Overview


The majority of the terminal units installed in high velocity systems prior to the mid-1970's were constant volume units. These constant volume systems featured relatively high rates of air change, maintaining space comfort by either the continual mixing of hot and cold air (dual duct systems), or by the addition of reheat to the supply air (terminal reheat system). Generally these systems supplied, at a constant air volume rate, the same temperature of cooling air to both interior and perimeter control zones.

When these systems were designed and installed, energy costs were low, and the energy consumption of the constant volume system was not considered to be a penalty at that time.

This is certainly not the case today. For a constant volume system, the total system air volume is the sum of all of the peak cooling loads that could occur on a design day. These individual peak loads occur in various control zones at various times during the day, due to a shifting sun load and variations in occupancy levels.

For a variable volume system, the total system air volume is the total instan­taneous peak cooling load that could occur on a designated day, at a specific time of that day. The instantaneous overall peak load is comprised of some control zones at peak demand, with other control zones at a reduced demand.

By utilizing the inherent diversity and adjusting the total system air volume to accommodate the instantaneous peak load, the total air volume for a variable volume system can be reduced to a much lower level than that for a constant volume system.

This potential reduction in total system air volume can contribute to significant savings in energy consumption. A variable volume system allows the supply air volume in any given control zone to vary as the cooling demand changes. Also the total fan power and the refrigeration load decrease directly in proportion to the actual cooling requirement.

In addition to reduction of fan power and cooling load, savings can be realized due to reduced heating costs when applied to dual duct and reheat systems. Energy wasteful reheat or dual duct mixing can be reduced or eliminated by converting to variable volume from constant volume.

Owners of commercial and institutional buildings are saving energy and money by converting their constant volume heating and air conditioning systems to variable volume. A major step in this conversion is the retrofitting of the existing constant volume terminal units to variable volume operation. This not only saves energy, but cuts heating and air conditioning costs dramatically.

Model IRDV

Design 75 VAV Regulator

Sources of cost saving energy reductions are as follows:

  • Reduced HP requirements for supply and return fans.
  • Reduced heating costs due to the reduction or elimination of reheat.
  • Reduced cooling costs due to the reduction in supply air volume.

Based on current experience with VAV systems, many of the older constant volume systems can be refitted to operate as a VAV system, at a substantial saving in energy, without any loss of occupant comfort.

Price offers a variety of options for retrofitting constant volume terminal units. These units are available with pneumatic, electronic or direct digital controls to suit any application.

Retrofit units are not certified by AHRI. Retrofit units do not currently fall within the scope of the AHRI Standard 880 Certification program.

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