13.6. NA7.5.2 Constant Volume, Single-Zone, Unitary Air Conditioner and Heat Pumps Systems Acceptance

NA7.5.2 Constant Volume, Single-Zone, Unitary Air Conditioner and Heat Pumps Systems Acceptance

Use Document NRCA-MCH-03-A

Purpose of the Test

This test verifies the components of a constant volume, single-zone, unitary air conditioner and heat pump system function correctly, including: thermostat installation and programming, supply fan, heating, cooling, and damper operation.

Testing of the economizer, outdoor air ventilation, and demand-controlled ventilation are located in the following sections of the Reference Appendices

NA7.5.1.2 Constant Volume System Outdoor Air Acceptance

NA7.5.4 Air Economizer Controls (if applicable)

NA7.5.5 Demand Control Ventilation (DCV) Systems (if applicable)

Instrumentation

Temperature meter, amp meter

Test Conditions

Unit and thermostat installation and programming must be complete.

HVAC system must be installed and ready for system operation, including completion of all start-up procedures, per manufacturer’s recommendations.

Document the initial conditions before overrides or manipulation of the setpoints and schedules. All systems must be returned to normal at the end of the test.

Estimated Time to Complete

Construction inspection: 0.5 to 1 hour (depending on familiarity with thermostat programming)

Equipment test: 1 to 2 hours

Acceptance Criteria

The following are verified through inspection:

Thermostat is located within the space conditioning zone that is served by the respective HVAC system.

Thermostat meets the temperature adjustment and dead band requirements of §120.2(b).

Occupied, unoccupied, and holiday schedules have been programmed per the schedule of the facility.

Preoccupancy purge has been programmed to meet the requirements of §120.1(c)2.

The following modes of operation function correctly:

Occupied heating mode operation: The supply fan operates continuously, all heating stages operate, cooling is not enabled, and the outdoor air damper is at minimum position.

Occupied operation with no heating or cooling load: The supply fan operates continuously, heating or cooling is not enabled, and the outdoor air damper is at minimum position.

Occupied cooling mode operation: The supply fan operates continuously, all cooling stages operate, heating is not enabled, and outside damper is at minimum position.

Unoccupied operation with no heating or cooling load: The supply fan shuts off, heating or cooling is not enabled, and the outdoor air damper is closed.

Unoccupied operation with heating load: The supply cycles ON, heating is enabled, cooling is not enabled, and the outdoor air damper is either closed or at minimum position.

Unoccupied cooling mode operation: The supply cycles ON, cooling is enabled, heating is not enabled, and the outdoor air damper is at minimum position.

Manual override mode: System reverts to occupied mode, the supply fan turns ON for duration of override, heating or cooling is enabled as necessary, and the outdoor air damper opens to minimum position.

Potential Issues and Cautions

Ensure that the supply fan runs continuously in occupied mode and cycles appropriately in unoccupied mode. Cycling refers to the supply fan running only when heating or cooling is enabled.

When testing the manual override, adjust the length of the override period to minimize test time. Be sure to reset the override period back to the correct length of time.

Tip: Overall test time may be reduced (especially for rooftop HVAC units controlled by thermostats) if two people perform the test − one to manipulate the thermostat while someone else verifies operation at the packaged unit.

The Energy Standards do not mandate the actual differential between occupied and unoccupied setpoints, only that the system must be adjustable down to 55°F for heating and up to 85°F for cooling and that the thermostat can be set for a 5°F dead band.

Setback control is only required for climates where the winter median of extremes is less than or equal to 32°F.

Setup control is only required for climates where the 0.5 percent summer design dry-bulb temperature is greater than or equal to 100°F.

Newly Constructed and Additions/Alterations: Applies only to new constant-volume, single-zone, unitary units with direct expansion (DX) cooling. These units may be cooling only or heating and cooling.

The following acceptance test procedures are applicable to systems controlled by thermostats, internal DDC, or central DDC systems. Most of the tests can be performed through simple manipulation of the thermostat or the DDC system controlling each packaged HVAC unit. Specific details and examples of how to perform each test are provided below.

1. Thermostat, or temperature sensor, is within the zone that the respective HVAC system serves.

2. Thermostat is wired to the HVAC unit correctly. This can be inferred from the acceptance tests.

3. In particular, ensure that multiple stage terminals (that is, first and second stage wires) on the thermostat, both cooling and heating stages, are wired to the corresponding circuits at the HVAC unit.

4. Verify that no factory-installed or field-installed jumpers exist across the first and second stage cooling terminals at the unit. (This will ensure that only the economizer can be enabled as the first stage of cooling.)

5. For heat pumps only, verify the “O” terminal on the thermostat is wired to the reversing valve at the unit.

6. For heat pumps only, verify thermostat dip switch or programmable software is set to heat pump.

7. Thermostat meets the temperature adjustment and dead band requirements of §120.2(b): The thermostat shall allow a heating setpoint of 55°F or lower and a cooling setpoint of 85°F or higher. The dead band shall be at least 5°F, where heating and cooling is shut off. On the acceptance document MECH-04A, note the minimum heating setpoint, maximum cooling setpoint, and dead band.

8. Occupied, unoccupied, and holiday schedules have been programmed per the schedule of the facility.

Preoccupancy purge has been programmed to meet the requirements of §120.1(c)2. This is typically accomplished by scheduling the unit to start one hour prior to actual occupancy. Check the method used to determine preoccupancy purge:

• The lesser of 15 cfm per person, or the conditioned floor area times the ventilation rate from the Energy Standards Table 120.1-A,

The following procedures are applicable to systems controlled by a programmable thermostat, internal DDC (packaged systems only), or central DDC system.

As you complete each step, check the appropriate operating mode boxes on the acceptance document.

Step 1: Disable economizer control and demand-controlled ventilation systems (if applicable) to prevent unexpected interactions.

The economizer can be disabled by temporarily adjusting the high-limit setpoint. The demand-controlled ventilation system can be disabled by setting the CO₂ setpoint well below current zone CO₂ concentration.

• Either set the “occupied” time schedule to include actual time or adjust the time to be within the “occupied” time schedule.

• Ensure all available heating stages operate; the heater stages on. This may require raising the heating setpoint even further so that multiple heating stages can become enabled. For example, many programmable thermostats and DDC control algorithms use time delays and deviations from setpoint to enable multiple heating stages. Setting the heating setpoint very high should prevent the first stage of heat from meeting setpoint and allow the system adequate time to enable the second or third stages.

• Outdoor air damper is open to minimum ventilation position (Note: Outdoor ventilation air requirements will be tested under section NA7.5.1.2 Constant Volume System Outdoor Air Acceptance).

Step 3: Simulate operation in the dead band (no-load condition) during occupied condition.

• Set “occupied” time schedule to include actual time or adjust time to be within the “occupied” time schedule (whichever is easier).

• Adjust heating and cooling setpoints so that actual space temperature is between the two values.

• Set “occupied” time schedule to include actual time or adjust time to be within the “occupied” time schedule (whichever is easier).

• Ensure all available cooling stages operate; the compressor stages on. This may require lowering the cooling setpoint even further so that multiple cooling stages can become enabled. For example, many programmable thermostats and DDC control algorithms use time delays and deviation from setpoint to enable multiple cooling stages. Setting the cooling setpoint very low should prevent the first stage of cooling from meeting set point and allow the system adequate time to enable the second stage.

Step 5: Simulate operation in the dead band (no-load condition) during unoccupied condition.

• Set “unoccupied” time schedule to include actual time or adjust time to be within the “unoccupied” time schedule (whichever is easier).

• Ensure actual space temperature is in between unoccupied heating and cooling setpoints. Adjust each setpoint as necessary to achieve desired control.

• Set “unoccupied” time schedule to include actual time or adjust time to be within the “unoccupied” time schedule (whichever is easier).

• Engage the manual override, which may entail pushing an override button, triggering an occupant sensor, or enabling some other form of override control.

• System reverts back to an “occupied” condition. For a DDC control system, verify the “active” heating and cooling setpoints correspond to those programmed for the occupied condition. For a programmable thermostat, the thermostat may display that it is in the “occupied” mode.

• System reverts back to an “unoccupied” condition when manual override period expires. It may be necessary to adjust the length of the override period to minimize test time.

Ensure all schedules, setpoints, operating conditions, overrides, and control parameters are placed back at the initial conditions. Confirm testing results on the certificate of acceptance document NRCA-MCH-03-A.