D-PAC Functionality Factory Testing Ease of Installation Ease of Maintenance Energy Efficiency

Digital Precise Air Control System D-PAC Functionality Factory Testing Ease of Installation Ease of Maintenance Energy Efficiency AAON • 2425 South Yukon Avenue • Tulsa, Oklahoma 74107 • (918) 583-2266 • Fax (918) 583-6094 • www.aaon.com Total Control Indoor Air Quality and Comfort ndoor air quality (IAQ) and occupant comfort are two of the most Scroll compressor, return important factors to consider with any HVAC system design. One air bypass, and modulating ofI the leading causes of poor IAQ and occupant discomfort is too hot gas reheat for energy much moisture in the air, commonly referred to as high humidity. efficient load matching IAQ problems associated with high humidity include mold growth, humidity control. An AAON condensation and increased sickness and allergic reactions. As for D-PAC controller is also occupant comfort, the saying goes “It’s not the heat, it’s the humidity”. factory installed to provide Improving indoor air quality and occupant comfort by controlling optimum performance of the the humidity and the temperature will help with these problems, system. Thus, the D-PAC boost productivity, and even improve the general well-being of the system provides an energy occupants. efficient, cost effective solution for temperature One way to improve IAQ and occupant comfort is with uniform and humidity control. humidity and temperature control. Ideally indoor conditions should remain consistently around 75°F dry bulb and 45% relative humidity. This will keep the occupants comfortable and decrease the likelihood The Competition of IAQ issues. ome in the HVAC industry assume that as Energy Use theS dry bulb temperature ontrolling both temperature and humidity can be very energy is being controlled the intensive. This is because both the sensible (temperature) and humidity will be controlled latentC (humidity) loads require energy from the HVAC equipment to as well. This, however, is be controlled. With a conventional rooftop unit extra energy is used to not true at many ambient satisfy the sensible load during part load conditions because cooling is conditions and space loads staged with only a few compressors which will not always match the with higher humidity. load. To satisfy the latent load the system must either satisfy the latent Humidity is also especially load while satisfying the sensible load, include an energy recovery uncontrollable when in wheel to reduce the outside air load, or there must be some form of ventilation mode, when cooling and reheating to dehumidify the air and avoid overcooling the the mechanical cooling is space. Satisfying the latent load while satisfying the sensible load and off and outside air is being including an energy recovery wheel will not control the humidity at introduced into the system. all conditions. Cooling and reheating will control the humidity at all Previously there have been conditions, however, it uses extra energy. only a few solutions for controlling both temperature The Solution and humidity. he AAON energy efficient rooftop unit solution to improving One method is to have a indoor air quality and occupant comfort by controlling both chiller and boiler system temperatureT and humidity is the patented Digital Precise Air Control with air handling units. This System, D-PAC (Patent No. 6,792,767). method allows modulation The system uses a Digital Scroll™ compressor, with modulating of both cooling and capacity control, for energy efficient load matching temperature control. reheating for tight control of For humidity control the system uses a combination of the Digital temperature and humidity. 2 The D-PAC System The problems with this system are that it is large, expensive to implement, and energy is wasted controlling the humidity because both the chillers and boilers must be running. Figure 1: Loaded State Figure 2: Unloaded State The second solution is a conventional rooftop unit with on/off hot gas reheat. What is D-PAC? The problems with this he D-PAC control system consists of a Digital Scroll compressor, system are there is poor modulating hot gas reheat, an economizer with three independently control of the amount controlledT sections - outside air, return air, and return air bypass - and an of reheat, there will be AAON D-PAC controller. uncomfortable discharge air temperature swings during The Digital Scroll Compressor varies the volume of refrigerant that operation, especially in flows through the cooling system. This allows the compressor to match make up air applications, the load needed by the unit. The compressor can modulate from 10-100% and finally the temperature of its cooling capacity. This allows the unit to have tighter temperature is still only controlled by a control than a conventional few compressor stages. unit. The compressor will 16 Digital Scroll 14 also run for a longer period r 12.8 so es The last solution is to use pr m of time, dehumidifying the 12 o C y 10.4 an energy recovery wheel it c air more and cycling the a 10 p a rd to control humidity. This, C da le n compressor on and off less. b ta 8 ia S r or however, is not a total a ss V pre 6 om y C solution because at higher The compressor operates cit pa Ca 4 d xe latent loads humidity will in two states, loaded and Fi Energy EciencyEnergy Ratio still be an issue. unloaded, to be able to 2 % modulate from 10-100 0 Reduced Load & Maximum Load & (Figure 1 and 2). The loaded Ambient Temperature Ambient Temperature state is the standard scroll Figure 3: Unit with a Digital Scroll compressor compressor operation. compared to a unit with a fixed capacity scroll During the unloaded state compressor and hot gas bypass. a solenoid valve opens and the top of the scroll moves up separating from the bottom of the scroll allowing refrigerant to circulate back to the suction line and keeping it from leaving out the discharge line. There is a power reduction during this unloaded state that allows the compressor and unit to save energy at part Digital Scroll load conditions (Figure 3). By pulsing between the loaded and unloaded Compressor states the capacity of the compressor can be varied for energy saving load matching capability. 3 Evaporator Mixed Air (MA) The Return Air Bypass Reheat Coil Coil Filters feature consists of an economizer with three independently controlled sections - outside air, return air, and return air bypass (Figure 4). The outside air damper routes all of the Outside Air (OA) ventilation air through the evaporator coil. The return Return Air Bypass air damper routes return Economizer air through the evaporator coil. The return air bypass damper routes up to 50% of the return air around the Supply Air after Return Air Bypass Cooling Coil Return Air (RA) evaporator coil. This allows and Modulating Hot Gas Reheat Leaving Air (CCLA) the mixed return and outside (RAB + MHGR) air to be dehumidified by the evaporator coil and Figure 4: D-PAC Airflow then reheated by the return air bypassed around the The Modulating Hot Gas Reheat feature coil. The cooling load is consists of a reheat coil downstream of the increased when return air is evaporator coil, a modulating reheat hot bypassed because the mixed gas valve, a modulating condenser hot gas air entering the evaporator valve, and a reheat controller (Figure 5). The coil contains a greater evaporator coil cools the mixed air to below percentage of outside air; the the dew point and then reheats the air with mixed air is not pre-cooled the reheat coil. The modulating valves allow by the bypassed return air. only the needed amount of reheat to be used, Return air bypass is an creating consistent supply air temperature. To energy efficient solution to minimize energy usage, reheat begins only controlling light humidity after the return air bypass damper is fully loads. open with the D-PAC System. Modulating hot Modulating Hot Gas gas reheat is an energy efficient solution to Reheat Control Valve controlling high humidity loads. The AAON D-PAC Controller controls the fans, outside air, return air, and return air bypass actuators, modulating hot gas reheat, compressors, heating, and optional AAONAIRE® energy recovery wheel. Using these components, the controller controls the temperature and humidity of the space under all conditions in the most energy efficient manner. The controller is factory installed and tested to ensure proper operation. The WattMaster WattMaster VCM-X controller and the AAON JENEsys controller are VCM-X Controller available for the D-PAC system to meet any controls application. With a choice of these factory installed controllers a D-PAC unit can used as a stand alone unit or integrated into an existing building automation system. The factory installed and tested D-PAC unit controller optimizes performance of the complete D-PAC system. AAON JENEsys Controller 4 Why Use a Digital Scroll Compressor? Sequence of Operation There four common ways to modulate the refrigerant capacity of a s the space temperature cooling system: hot gas bypass, multiple compressors, an inverter driven Aincreases or decreases, compressor and a Digital Scroll compressor. the controller modulates A hot gas bypass system mixes hot refrigerant gas from the compressor the compressor’s capacity with cool refrigerant liquid at the evaporator to control the cooling capacity. to maintain the space Hot gas bypass is an inefficient modulation technique because it is adding temperature setpoint. a false load that the system must satisfy. As the space humidity rises, A multiple compressor system stages the compressors on and off to the controller modulates control the cooling capacity. The problem with this system is that it has the compressors capacity to a finite number of capacity steps for modulation and will have inefficient maintain a low evaporator operation at many part load conditions.

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