The Air Handling Unit (AHU) preheat coil valve was leaking when signaled closed (0% valve signal), resulting in a preheat discharge temperature that was over 40 degrees warmer than the required temperature. As a result, the cooling coil valve opened simultaneously to maintain the final supply air temperature at its setpoint of 55°F. The simultaneous heating and cooling resulted in excess heating and cooling costs. Continue reading “Simultaneous Heating & Cooling”
The building is 275,000 sq. ft. It has over 7,500 Siemens BAS points monitored, 725,000 samples per day, 4 chillers, 4 cooling towers, 12 pumps, 9 air handling units, and over 1,000 terminal units.
Sample AHU Operating Conditions
Figure below shows the base and post operation of the 3 main AHUs in the building. Prior to the modifications, all 3 AHU supply fans were pegged at 100% speed, the air change per hour (ACH) rates were over 15 in many labs and the building initially had an energy intensity of 366 kBTU/sq. ft./yr. Continue reading “Life Science Building: Sample AHU Operating Conditions”
Pneumatic actuator leak
The building HVAC systems are controlled via a DDC front end connected to pneumatic actuators out in the field. The heating and cooling valves for a large 100% outdoor air-handling unit (AHU) were operating off of a common pneumatic air feed to the valve actuators. The pneumatic line developed an air leak that caused the actuators to not open and close correctly.
In this example we will show you how Analytika service helped to solve simultaneous heating and cooling issue.
The Air handler (AHU) discharge air temperature (DAT) setpoint was overridden from the sequence of operation and reduced from 55˚F to 51˚F. As a result, the cooling coil valve was opening to maintain the lower DAT and consequently requiring additional heating downstream. This resulted in additional heating and cooling costs. Continue reading “Simultaneous heating and cooling issue”
Four (4) large air handling units (AHUs) in one of the buildings have heat recovery; however, only two (2) were operating efficiently.
The heat recovery system supplies a 50% glycol solution to the four (4) heat recovery coils in AHU-1A, AHU-1B, AHU-1C, and AHU-1D. The system utilizes a single 100 HP constant flow pump which operates when the outside air temperature decreases below 54°F and is disabled when the outside air temperature rises above 55°F. Continue reading “Heat Recovery Performance Verification”