Efficiency Recommendations

All equipment must meet DOE and local building code standards, which usually reference ASHRAE 90.1. By law, DOE is required to maintain the federal minimum-efficiency standards at levels at least as stringent as the most recent revision of ASHRAE 90.1. ACEEE recommends buying more efficient equipment instead of baseline units. In general, the premium price of more efficient equipment is recovered quickly for commercial unitary equipment because it is generally used many more hours per year than residential equipment in the same climate zone. The recommended minimum level from the New Buildings Institute is also the Consortium for Energy Efficiency Tier 2 level.

Consortium for Energy Efficiency Tier 2 recommendations, corresponding to ENERGY STAR for units larger than 65,000 Btuh, point toward very efficient packaged air conditioners and heat pumps. Federal Energy Management Program materials are also excellent; the site includes cost-effectiveness calculation methods. ENERGY STAR and CEE both set 85% AFUE as their recommendation for efficient "small" boilers. In cold climates, condensing boilers may be very cost-effective (AFUE at least 90%).

Sizing

There are enough unique situations in selecting the proper packaged air conditioning unit that a heating and cooling load calculation should always be done. Using rules of thumb for sizing is inaccurate and not recommended. Correctly sizing the cooling capacity of a unit must take into consideration the envelope load (orientation, windows, walls, and roof), the internal heat gains (lights, people, and equipment), and the ventilation load. Ask the designer to submit calculations for your records. At least you will know if she/he did them. ASHRAE and other sources have proven methods for calculating heating and cooling loads.

Once the calculations are complete, the unit should be sized to barely meet the maximum demand under the ASHRAE design temperature for the location. Oversized units consume more energy than units sized for the expected load. Furthermore, oversized units cause space temperature fluctuations as the compressors "short-cycle" in an attempt to meet part-load conditions. A common refrain from designers is that they oversize equipment so that it will have capacity to warm up or cool down the space quickly after a prolonged night setback. However, during the unoccupied warm-up cycle the ventilation air is off and any capacity in the equipment for ventilation serves as a cushion.

Layout and Installation

Lifecycle efficiency depends on access and clearance for service and maintenance. Units that are not serviced regularly become energy "hogs." When equipment is crammed into a ceiling or attic space, and a service technician has to stand on a ladder in a busy office to service the unit, chances are the unit will not be serviced regularly. When planning for proper maintenance access, take into consideration that filters must be changed (sometimes quarterly); electrical panels must be accessible; and compressors, fans, belts, shafts, bearings, and coils must occasionally be replaced.

Adequate clearance must be afforded to the intake and exhaust of the air-cooled equipment. Locating an air-cooled unit too close to a wall or in a pit can restrict the proper airflow or cause recirculation of the heat rejected from the fan. Putting multiple condensers near each other in a "pen" or enclosure can lead to cross-feeding hot exhaust air from one to the cooling fins of adjacent units under some conditions. Split-system air conditioners and heat pumps require careful design of refrigerant piping. Returning lubricating oil from the piping and coils to the compressor is a major concern. Outdoor units should be located as close to Indoor units as possible. There are restrictions on how high above and how far below the outdoor unit can be relative to the indoor unit. Improper refrigerant piping design can waste energy and operating dollars.

In selecting outdoor packaged equipment for either humid locations or very cold climates, special attention needs to be paid to cabinet insulation and sealing. Additional insulation may be needed to prevent condensation from forming on the outsides of casings, and doors may need to be tightly sealed to prevent leakage. Since packaged units are manufactured on an assembly line, careful inspection must be given at the time of installation to assure that these issues are addressed.

Completion (Commissioning) Requirements

Of prime importance to successful long-term energy efficiency are the steps taken at the time of project completion to assure that the packaged equipment and systems are working properly and that an orderly transition occurs from the contractor to the owner. Activities include:

• Startup and testing of all equipment

• Owner training on operation

Reports documenting these activities include:

• Testing, adjustment, and balancing (TAB) reports
  
  
• Drawings of the as-built installation
  
  
• Narrative descriptions of all systems (may not be required on through-the-wall and single-zone systems)
  
  
• Complete operation and maintenance manuals including:
  
  
  • locations of qualified service agencies
    
    
  • data on each piece of equipment (i.e., capacities, options, etc.)
    
    
  • operating instructions for each piece of equipment
    
    
  • preventative maintenance measures
    
    
  • electrical wiring diagrams
    
    
  • spare parts list
    
    
  • control sequences

Service and Maintenance

Some owners of larger buildings (or multiple buildings) employ full-time maintenance staff, but owners of smaller buildings usually make other arrangements. If you do not have full-time staff available for maintenance, it is wise to retain a qualified maintenance service organization. Some owners choose to wait until the equipment fails before calling a service company, but this may cost more in the long run in repairs and higher bills. Even smaller buildings with packaged equipment may be complicated enough to require the services of a qualified service company.

Your maintenance program should at minimum include the following:

• Regular air filter changes (this may be required on a quarterly basis)
  
  
• Annual verification of the operation of critical elements such as fan belts, compressors, and dampers
  
  
• Cleaning cooling coils, condenser coils, fans, and condensate drains
  
  
• Verification and calibration of controls
  
  
• Checking refrigerant levels-too low or too high impacts energy performance
  
  
• Checking gas-burning equipment