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by Paul Nalewajk

Why should a retailer perform post construction HVAC inspections?

Post Construction Surveys are essential for the following reasons:

  1. Equipment, ductwork, piping, etc. are not always installed properly
    • Engineers and architects do not typically visit store sites prior to developing a design. If field conditions require that the installed system does not exactly follow the design drawings, the installing contractor makes design changes which may or may not be appropriate.
    • HVAC contractors and subcontractors can make honest mistakes.
    • Unscrupulous contractors and subcontractors will delete items from the work scope to increase their profits, or to reduce their losses, if there is no threat of a detailed inspection.
    • Sometimes, a general contractor will allow a subcontractor to make changes to the work scope in order to meet a budget price.
    • HVAC contractors may order or obtain equipment, which differs from the specified equipment.
    • HVAC contractors do not necessarily use skilled service technicians to perform the commissioning and start-up of new equipment.
  2. HVAC system deficiencies do not appear on the project manager’s punch list
    • Most HVAC system components are not visible.
    • It takes a great deal of specialized training to determine if the equipment was installed properly with the correct accessories.
    • Equipment operation can only be checked fully by a trained technician.
    • A system may be started up during the heating season and operate in a satisfactory manner, however it may not operate during the cooling season.
    • Many HVAC problems are only noticeable to laymen, and occupants when the system is operating under full load conditions.
    • Some deficiencies may not be noticeable to occupants, however they shorten equipment life, cause excessive energy usage, or affect indoor air quality.
    • Some deficiencies cause problems, which may not appear for years.
    • Project managers are not trained adequately to inspect HVAC systems.
  3. Examples of deficiencies found on post construction inspections of retail stores
    • Found that economizers were neither furnished or installed. Units would heat and cool, but no outdoor air was brought in for ventilation there was no ability to provide cooling using outdoor air. (A process which saves 25% of compressor run time.)
    • Found no toilet exhaust, but test and balance report shows toilet exhaust to be operating at 10% above the specified capacity. Found the duct to toilet exhaust fan blanked off below the fan. There is no way this fan ever moved any air from the bathrooms at this facility.
    • Found the contractor used unshielded cable between the thermostat and the remote temperature sensor. The thermostats would lock-up on an intermittent basis, not allowing a change of set point and causing continuous heating and cooling.
    • Found thermostats configured to use internal temperature sensors rather than remote temperature sensors. All thermostats at this location were responding to the temperature in the manager’s office rather than the temperatures within the conditioned zones. When the manager’s office got warm, the entire store got cooling. When the office got cool the entire store received heat.
    • Found two remote sensors wired to the wrong thermostats. When thermostat #1 called for cooling, the space served by unit #2 was over cooled, causing thermostat #2 to call for heat, overheating the space served by unit #1. This caused one unit to remain constantly in the cooling mode, one unit to remain constantly in the heating mode, the store to be severely uncomfortable, and extremely high utility costs.
    • Found contractor had energized compressors without opening discharge service valves, causing the head gaskets to be blown on 6 compressors. Start-up of equipment occurred in winter therefore store was heated adequately, and cooled adequately by the economizer.
    • Found a unit set flush to wrong side of the roof curb. Approximately 25% of the return opening in the bottom of the unit was open to the outdoors, causing the unit to bring in at least 50% outdoor air.
    • Found that the contractor had installed a 4 in waste vent below and within 3 feet of the outdoor air intake for a rooftop unit. The store staff couldn’t understand why the break room smelled like a sewer.
    • Found units circulating 50% of the specified air volume. The store was comfortable but the compressors were cycling off on low-pressure safety controls, and gas heat was cycling on and off on the high limit safety controls.
    • Found control transformers set up for 230 volts when actual line voltage was 208 volts. Units were operating fine, but during peak load days, drops in the utility line voltage would cause these units to drop out as the control voltage dropped below the minimum acceptable threshold.
    • Found no low ambient controls were installed. The unit was operating fine in mild weather, however the compressor would be destroyed if the unit were allowed to operate during winter.
    • Found that not all air outlets were connected to supply duct. One department of the store seemed too warm. The technician found that a 20-foot section of supply trunk duct was never installed, eight ceiling diffusers were not receiving any air, and the unit was discharging into the ceiling plenum space.
    • Found a roof curb was assembled wrong. One department appeared too warm and the roof membrane was billowing near one unit. The technician found that the wrong areas of the roof curb had been blanked off. The unit was discharging into the corrugations between the Q deck and the roof insulation instead of discharging entirely into the supply duct.

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