Knowledge Centre – Passive Strategies

Design
Introduction
Sizing
Controls
Equipment Efficiency
Optimized Delivery

Introduction

Following key steps are important for energy efficiency in comfort systems:

  1. Use of sustainable design feature to reduce the energy requirement for heating, cooling, and ventilation
  2. Different spaces have different cooling requirements based on surrounding conditions and functional use. For eg, a space next to a glazed area would have more cooling requirement in summer compared to any space which is less exposed to glazed area. Thus, designer to focus to zone all spaces with similar conditioning requirement together.
  3. Define the optimized set points as per the thermal comfort model of India
  4. Many different systems are available in the market with different efficiency range and cost. Select the correct system applicable based on the functional requirement, energy efficiency concerns, and operational use.
  5. Integrate systems like demand controlled ventilation and energy recovery system to reduce the system size
  6. Application of economizers, evaporative cooling & condenser, and natural ventilation could reduce the operational energy use significantly.
  7. Design the system with optimized pressure drop and frictional losses to reduce the fan and pump sizes. Application of VFD in these systems should also be looked into for best efficiency
  8. Select best possible energy efficient equipment for each component under selected comfort system.
  9. Controls should also be integrated into the design for reducing operational energy use based on the schedule and occupancy.
  10. Explore the possible use of low energy comfort systems like radiant cooling, three stage evaporative cooling etc. to replace the conventional comfort system.

HVAC design and equipment selection majorly depends on:

  • Building functional use, type, and operational schedule
  • Variation in operational schedule and potential of system controls
  • System complexity
  • Commissioning – pre occupancy and post occupancy Design

Sizing

Correct sizing of an air conditioning equipment is one of the key factor for energy efficiency. Installation of oversized system is common mistake in building industry penalizing the building with high capital and operational cost. Designer oversize the system based on thumb rules without estimating the accurate cooling load based on building design. Key disadvantages of oversized equipment are as below:

  1. Non uniform cooling
  2. System running at lower capacity are inefficient. For example, a 300 ton chiller running at 100% capacity is far more efficient than 600 ton chillers running at 50% capacity.
  3. Higher capital cost and operational cost

Effort should be made to assess in detail the occupancy pattern of the space. If the facility is more likely to operate at a fraction of the peak load most of the time, the part-load efficiency of the central plant will be a better indicator of the system performance than peak-load efficiency. If required, different types of ACs may be selected for different parts of the building. For instance, split units may serve guest rooms best, while a packaged outdoor unit may be best suited for an intermittently occupied space like a meeting room.

Controls

Controls are very useful in the commercial buildings to optimize the energy use with respect to varying operational schedule, occupancy schedule, and difference in heating/ cooling requirement in different spaces.  Many types of controls are available in the market like – occupancy controls, set point controls time clock control etc.

Energy saving potential by controlling the fluid flow as per the requirement is substantial. Controls like variable frequency drive and variable speed drive controls the fluid flow when the requirement is not 100% of the design conditions. The controls reduce the pump rate or fan speed and cut down on the energy use.

Equipment Efficiency

Chiller Efficiency
Chiller efficiency is amount energy consumption in watt for per ton of cooling produced and is rated in kW/ ton or coefficient of performance (COP) or energy efficiency ratio (EER). The efficiency are considered either in full peak load or part load (IPLV). ECBC states the minimum requirement of COP for each chiller type and size. The table is listed below. For a NZEB, effort should be made to exceed the efficiency requirement stated in the table.

BEE’s star rating program
Bureau of Energy Efficiency (BEE), a statutory body under Ministry of Power, has launched the standards and labelling program in 2006. The objective of this program is to develop the energy efficiency standards for each appliance. Under this program, for the benefit of general public, the appliance bears a BEE Star Label showing the level of energy consumption by the appliance both in terms of absolute values as well as equivalent number of stars varying from one to five, in accordance with specific stipulation. The greater the number of stars on the label, higher the appliance energy efficiency and lower its electricity consumption. Many appliances have already been covered under this program like refrigerators, air conditioners, washing machine etc. BEE has an objective to star rate all possible appliances with high energy saving potential. Apart from this small scale appliances in residential sector, BEE has also started the program to star rate the large scale appliances used in commercial buildings like chillers, VRFs, transformers etc. Star rating program for buildings has also been developed to star rate the overall efficiency standard of a building.

Optimized Delivery

Some simple steps to ensure correct installation go a long way in realizing optimal performance and energy efficiency. The best rated systems often underperform because of improper installation. For existing systems as well as new systems, it is advisable to pay attention to the location of the supply and return registers, location of the unit itself, insulation of ducts, and placement of the thermostat:

  • Ensure that all ducts are firmly sealed and well insulated
  • Refrigerant piping must have as few bends as possible
  • Supply registers or indoor units are not located close to or opposite doors or entry points
  • Locate the condensing unit away from the space to be served, if possible (these units tend to be noisy)
  • The condensing unit should be located such that it has an uninterrupted flow of air and stays cool and shaded
  • The initial refrigerant charge and air flow rate of the system should be verified to be the same as guaranteed by its manufacturer’s specification
  • The thermostat should be located at a thermally neutral spot, i.e., away from windows, supply registers, light fixtures, and appliances that may produce heat
  • It is a good practice to plan and allow adequate indoor space for the installation, maintenance, and repair of the system.