Dedicated outdoor air systems (DOASs) provide HVAC designerswith opportunities for advantages in simplicity, efficiency, and economy.This book represents the most complete and up-to-date guidance onthe design, installation, and operation and management of DOASs innonresidential applications. Guided by the information in this book, HVAC system designers will beable to optimally incorporate DOASs into their projects. Architecturaldesigners, building developers and owners, maintenance professionals,students, teachers, and researchers may also find the contents useful. Keywords: DOAS, dedicated outdoor air systems, systems design, outdoor air, system heating and cooling, efficiency<\/p>\n
| PDF Pages<\/th>\n | PDF Title<\/th>\n<\/tr>\n | ||||||
|---|---|---|---|---|---|---|---|
| 6<\/td>\n | Chapter 1: Introduction 1 Chapter 2: Outdoor Air and Load Requirements 9 Chapter 3: System Selection 29 Chapter 4: Detailed Design Considerations 49 <\/td>\n<\/tr>\n | ||||||
| 7<\/td>\n | Chapter 5: Controls 77 Chapter 6: Construction 107 Chapter 7: Operation and Maintenance 119 <\/td>\n<\/tr>\n | ||||||
| 8<\/td>\n | Appendix A: Sample DOAS Installation Checklist 127 Appendix B: Sample DOAS Operational Checklist 135 References 137 <\/td>\n<\/tr>\n | ||||||
| 14<\/td>\n | Figure 1.1 Changing seasons. <\/td>\n<\/tr>\n | ||||||
| 15<\/td>\n | Why This Book Was Written Humidity Control <\/td>\n<\/tr>\n | ||||||
| 16<\/td>\n | Figure 1.2 Annual cumulative latent (dehumidification) and sensible-cooling load from ventilation air. <\/td>\n<\/tr>\n | ||||||
| 17<\/td>\n | Figure 1.3 Design extremes. Energy Impacts <\/td>\n<\/tr>\n | ||||||
| 18<\/td>\n | Figure 1.4 Demand-controlled ventilation benefits. <\/td>\n<\/tr>\n | ||||||
| 19<\/td>\n | Ventilation Control Systems without Ventilation Capabilities First Cost Reduction <\/td>\n<\/tr>\n | ||||||
| 22<\/td>\n | Figure 2.1 A heavy occupant load. <\/td>\n<\/tr>\n | ||||||
| 24<\/td>\n | \u2022 Code-Driven Airflow. The outdoor airflow delivered is based on the minimum required by building codes or standards. \u2022 Exhaust-Driven Airflow. Certain spaces\/buildings require more exhaust air than outdoor air (for example laboratories or facilities with many bathrooms). To make up for (or replace) this exhausted air, more outdoor air is brought into the building… \u2022 Load-Driven Airflow. For a DOAS, the types of loads that may result in increasing outdoor airflow typically involve dehumidification or humidification. As an example, if chilled ceilings or passive chilled beams are being used in a space, the des… Example Calculations <\/td>\n<\/tr>\n | ||||||
| 25<\/td>\n | Figure 2.2 Example office building. Vbz = (Rp \u00d7 Pz) + (Ra \u00d7 Az) <\/td>\n<\/tr>\n | ||||||
| 26<\/td>\n | Voz = Vbz \/Ez Table 2.1 Zone Air Distribution Effectiveness Ez <\/td>\n<\/tr>\n | ||||||
| 27<\/td>\n | Table 2.2 DOAS Ventilation Calculations for Example Office Building (Cooling Design) <\/td>\n<\/tr>\n | ||||||
| 28<\/td>\n | Vot = sum of Voz <\/td>\n<\/tr>\n | ||||||
| 29<\/td>\n | Figure 2.3 Occupancy-driven variations in outdoor air requirements. <\/td>\n<\/tr>\n | ||||||
| 30<\/td>\n | (b) Figure 2.4 Dallas-Fort Worth, TX, outdoor design conditions, (a) I-P, (b) SI. Variability <\/td>\n<\/tr>\n | ||||||
| 31<\/td>\n | Figure 2.5a Variability in outdoor air conditions (I-P). <\/td>\n<\/tr>\n | ||||||
| 32<\/td>\n | Figure 2.5b Variability in outdoor air conditions (SI). <\/td>\n<\/tr>\n | ||||||
| 33<\/td>\n | Figure 2.6 Preconditioning benefits of enthalpy energy exchangers. <\/td>\n<\/tr>\n | ||||||
| 34<\/td>\n | Figure 2.7 Total-energy (enthalpy) wheel in cooling mode. <\/td>\n<\/tr>\n | ||||||
| 35<\/td>\n | Dehumidification Figure 2.8 Using DOAS to address latent loads. <\/td>\n<\/tr>\n | ||||||
| 36<\/td>\n | Figure 2.9 Wraparound heat pipe. <\/td>\n<\/tr>\n | ||||||
| 37<\/td>\n | QL = 0.69 \u00d7 Voz \u00d7 (Wspace \u2013 Wca) I-P QL = 3.0 \u00d7 Voz \u00d7 (Wspace \u2013 Wca) SI Cooling <\/td>\n<\/tr>\n | ||||||
| 38<\/td>\n | Table 2.3 Required Dew Point of Conditioned OA for Example Office Zones Humidification <\/td>\n<\/tr>\n | ||||||
| 39<\/td>\n | Figure 2.10 DOAS unit used to add humidity to outdoor air during cold\/dry seasons. Heating Air Cleaning <\/td>\n<\/tr>\n | ||||||
| 40<\/td>\n | Figure 2.11 Los Angeles skyline. <\/td>\n<\/tr>\n | ||||||
| 42<\/td>\n | Figure 3.1 Making choices. <\/td>\n<\/tr>\n | ||||||
| 43<\/td>\n | Conditioned Outdoor Air Supplied Directly to Each Zone <\/td>\n<\/tr>\n | ||||||
| 44<\/td>\n | Figure 3.2 Direct to zone\u2014local units. <\/td>\n<\/tr>\n | ||||||
| 45<\/td>\n | Figure 3.3 Direct to zone\u2014central AHU. <\/td>\n<\/tr>\n | ||||||
| 46<\/td>\n | Conditioned Outdoor Air Supplied to Intake of Local Units <\/td>\n<\/tr>\n | ||||||
| 47<\/td>\n | Figure 3.4 Air supplied to intake of local units. Conditioned Outdoor Air Delivered to Supply Side of Local Units <\/td>\n<\/tr>\n | ||||||
| 48<\/td>\n | Figure 3.5 Air supplied to supply side of local units. <\/td>\n<\/tr>\n | ||||||
| 49<\/td>\n | Conditioned Outdoor Air Supplied to Plenum near Local Units Figure 3.6 Air supplied to ceiling plenum. <\/td>\n<\/tr>\n | ||||||
| 50<\/td>\n | \u2022 Supply and\/or exhaust fans \u2022 Variable-speed drives \u2022 Air-to-air energy recovery devices (wheels, plate heat exchangers, heat pipes, and coil loops) \u2022 Desiccant dehumidification wheels \u2022 Cooling coils (DX and chilled-water) \u2022 Heating coils (hot-water, indirect gas-fired, or electric) \u2022 Humidifiers \u2022 Condenser heat recovery (reheat) coils \u2022 Motorized dampers \u2022 Filters or other air cleaning devices Cooling Coil and Reheat <\/td>\n<\/tr>\n | ||||||
| 51<\/td>\n | Exhaust Air Energy Recovery <\/td>\n<\/tr>\n | ||||||
| 52<\/td>\n | (a) <\/td>\n<\/tr>\n | ||||||
| 53<\/td>\n | (a) <\/td>\n<\/tr>\n | ||||||
| 54<\/td>\n | Energy Recovery and Sensible Reheat Energy Recovery and Desiccant Wheel <\/td>\n<\/tr>\n | ||||||
| 55<\/td>\n | (a) <\/td>\n<\/tr>\n | ||||||
| 56<\/td>\n | Climate Considerations <\/td>\n<\/tr>\n | ||||||
| 57<\/td>\n | (a) <\/td>\n<\/tr>\n | ||||||
| 58<\/td>\n | Figure 3.11 World map showing climate regions. <\/td>\n<\/tr>\n | ||||||
| 59<\/td>\n | Application Type\u2014New or Retrofit Additional Considerations <\/td>\n<\/tr>\n | ||||||
| 62<\/td>\n | Figure 4.1 Getting the details right. <\/td>\n<\/tr>\n | ||||||
| 63<\/td>\n | \u2022 Minimum equipment efficiencies <\/td>\n<\/tr>\n | ||||||
| 64<\/td>\n | \u2022 Fan power limitations \u2022 Use of an economizer \u2022 Use of exhaust air energy recovery \u2022 Requirements for simultaneous heating and cooling (as applicable to dehumidification) Minimum Equipment Efficiency Meeting ANSI\/ASHRAE\/IES Standard 90.1 Economizer Requirements <\/td>\n<\/tr>\n | ||||||
| 66<\/td>\n | Conditioned Outdoor Air Considerations \u2022 If outdoor air (OA) is delivered directly to the space through ceiling-mounted diffusers, Ez = 1.0 as long as the temperature of the conditioned OA is cooler than the temperature in the space. \u2022 If the OA is delivered to the intake of a local HVAC unit (a water-source heat pump or variable-refrigerant-flow terminal, for example) then Ez = 1.0 when the local unit delivers cool air, but may be 0.8 when it delivers warm air. \u2022 If the OA is delivered directly to the space through floor-mounted grilles or diffusers, Ez may be 1.0 or 1.2 (depending on velocity) as long as the temperature of the conditioned OA is cooler than the space temperature. If the air is delivered w… Demand-Controlled Ventilation <\/td>\n<\/tr>\n | ||||||
| 67<\/td>\n | Figure 4.2 Demand-controlled ventilation with a DOAS. <\/td>\n<\/tr>\n | ||||||
| 68<\/td>\n | Exhaust Air Considerations <\/td>\n<\/tr>\n | ||||||
| 69<\/td>\n | Louver Placement and Sizing <\/td>\n<\/tr>\n | ||||||
| 70<\/td>\n | Air Duct Design Recommendations \u2022 Outdoor air, supply air, and exhaust air ducts (leaving the DOAS unit) located indoors should be insulated and have a vapor barrier. \u2022 Insulated duct supports should be used to avoid compressing the duct insulation. \u2022 Exposed supply air ductwork routed within conditioned spaces should be constructed with double-wall insulation. \u2022 Consider ducted distribution rather than using ceiling or floor plenums for supply and recirculated return air. Plenums are very difficult to seal and clean, and can lead to problems with condensation. \u2022 Ducts should be sized for minimal pressure drop and duct fittings should include long radius elbows, smooth transitions, and takeoffs. <\/td>\n<\/tr>\n | ||||||
| 71<\/td>\n | Cooling Coil Design Tips <\/td>\n<\/tr>\n | ||||||
| 72<\/td>\n | Desiccant Wheels <\/td>\n<\/tr>\n | ||||||
| 73<\/td>\n | Preheating Cold Outdoor Air Reheating Dehumidified Air \u2022 Exception 1 allows simultaneous cooling and reheating of the same airstream if \u201cThe system is configured to reduce supply air volume to 50% or less of the design airflow rate or the minimum outdoor air ventilation rate specified in ASHRAE Stand… <\/td>\n<\/tr>\n | ||||||
| 74<\/td>\n | Figure 4.3 Neutral air drawbacks\u2014cooling wasted by delivering air to spaces at near space dry-bulb temperature (\u201cneutral\u201d). \u2022 Exception 5 allows simultaneous cooling and reheating of the same airstream if: \u201cAt least 90% of the annual energy for reheating\u2026 is provided from a site- recovered or site-solar energy source.\u201d Hot-gas reheat, an air-to-air energy recovery… <\/td>\n<\/tr>\n | ||||||
| 75<\/td>\n | \u2022 The greater the outdoor air requirements, the more operational savings will be achieved. This is true for applications with significant ventilation requirements as well as those with longer operating hours. <\/td>\n<\/tr>\n | ||||||
| 76<\/td>\n | Figure 4.4 Energy recovery wheel. \u2022 During humid weather, a dehumidification device is still needed. Even technologies that include latent heat exchange are not substitutes for a dehumidifier; they simply reduce and stabilize the dehumidification load. \u2022 Consider downsizing major cooling and heating plants. (In critical facilities such as operating rooms, the effects of reducing the size of cooling and heating equipment should be carefully reviewed.) \u2022 Consider installing bypass dampers. Depending on climate, there may be many hours during the year when outdoor air temperatures are cooler than the exhaust air but not so cold that heat is required; at these times, operating a heat exchanger coul… <\/td>\n<\/tr>\n | ||||||
| 77<\/td>\n | Total-Energy Recovery Devices Figure 4.5 Total-energy wheels. Sensible Energy Recovery <\/td>\n<\/tr>\n | ||||||
| 78<\/td>\n | Figure 4.6 Heat pipe operating principle. <\/td>\n<\/tr>\n | ||||||
| 79<\/td>\n | \u2022 there are more rows of pipes in the array, \u2022 the fin spacing is closer together, \u2022 air velocity through the array is slower, or \u2022 the heat pipe is inclined to promote liquid returning to the \u201cwarm\u201d end. Figure 4.7 Plate-type heat exchanger in a packaged system. <\/td>\n<\/tr>\n | ||||||
| 80<\/td>\n | ERR = (h1 – h2)\/(h1 – h3) (1) et = (mOA\/mmin) \u00d7 (h1 \u2013 h2)\/(h1 \u2013 h3) (2) <\/td>\n<\/tr>\n | ||||||
| 81<\/td>\n | Figure 4.8 Energy recovery example. <\/td>\n<\/tr>\n | ||||||
| 82<\/td>\n | Figure 4.9 Impact of unbalanced flow on energy recovery effectiveness and ERR. Space Pressurization and Energy Recovery <\/td>\n<\/tr>\n | ||||||
| 83<\/td>\n | Frost Prevention Figure 4.10 Frosted air-to-air heat exchangers: (a) plate heat exchanger and (b) wheel heat exchanger. <\/td>\n<\/tr>\n | ||||||
| 84<\/td>\n | Table 4.1 Common Frost Prevention Strategies for Air-to-Air Energy Recovery Devices \u2022 Integral Steam Absorption Coils. These are typically factory-installed devices located between the cooling coil and supply fan. Steam is generated using a gas- or electric-driven steam generator and introduced to the airstream through dispersion … <\/td>\n<\/tr>\n | ||||||
| 85<\/td>\n | \u2022 Duct-Mounted Steam Absorption Coils. These are typically installed in a straight section of ductwork adjacent to the outlet of the DOAS unit. Similar to integral coils, the steam is often generated locally using a gas- or electric-driven steam ge… \u2022 Evaporative Humidifiers. These are typically installed integral to the DOAS unit and are fed from either a pressurized water-atomizing or compressed air- fogging device located adjacent to the unit (Figure 4.11). Foggers produce many small drople… Particulate Contaminant Removal <\/td>\n<\/tr>\n | ||||||
| 86<\/td>\n | Figure 4.11 Compressed air fogger. Gaseous Contaminant Removal <\/td>\n<\/tr>\n | ||||||
| 87<\/td>\n | Figure 4.12 Particulate filter options. Prefilter <\/td>\n<\/tr>\n | ||||||
| 88<\/td>\n | Table 4-2 Optimal Solutions for VAV and DOAS Filters Giving Equal Performance Figure 4.13 Enthalpy wheels unprotected by filters. <\/td>\n<\/tr>\n | ||||||
| 90<\/td>\n | Figure 5.1 Mission Control Center at NASA\u2019s Johnson Space Center. <\/td>\n<\/tr>\n | ||||||
| 92<\/td>\n | Figure 5.2 Schematic diagram at left gives a quick overview of system function compared to plan view at right. <\/td>\n<\/tr>\n | ||||||
| 93<\/td>\n | Figure 5.3 DOAS unit control modes (outdoor air control). Table 5.1 DOAS Unit Control Modes <\/td>\n<\/tr>\n | ||||||
| 94<\/td>\n | Resetting Dehumidification Capacity Humidity Control During Unoccupied Hours <\/td>\n<\/tr>\n | ||||||
| 95<\/td>\n | Figure 5.4 After-hours humidity control. <\/td>\n<\/tr>\n | ||||||
| 96<\/td>\n | Methods to Avoid Too-Low Space Temperatures <\/td>\n<\/tr>\n | ||||||
| 97<\/td>\n | Figure 5.5 Demand-controlled ventilation. \u2022 To Avoid Low Space Temperatures at Part-Load Conditions. As a zone\u2019s sensible-cooling load decreases (because of milder outdoor air conditions, reduced solar heat gain, and\/or internal loads) the cold air supplied by the DOAS may provide more s… \u2022 Where Zone Sensible-Cooling Loads Are Highly Variable. In spaces such as hotels or dormitories, the sensible-cooling loads can vary significantly from room to room. This can potentially result in too-low space temperatures in those areas that hav… <\/td>\n<\/tr>\n | ||||||
| 98<\/td>\n | Figure 5.6 Activating heat in local units. \u2022 When Very Low Conditioned Outdoor Air Dew Point Is Required. For applications that have very high latent loads or require lower than normal space dew points, the outdoor air will need to be dehumidified to a very low dew point. In this case, the … <\/td>\n<\/tr>\n | ||||||
| 99<\/td>\n | \u2022 To Avoid Condensation in Ceiling Plenum. If outdoor air is introduced directly into a ceiling plenum space near the intake of local HVAC units (see Figure 3.6), it should be supplied at a dry-bulb temperature above the expected dew-point temperat… \u2022 Reset DOAS Leaving Air Temperature Based on Outdoor Air Temperature. A possible control approach is to activate the DOAS unit reheat coil (or air-to-air recovery device) based on outdoor air temperature (Figure 5.7). For example, if the outdoor a… The building automation system shall continuously monitor the outdoor dry- bulb temperature. \u2022 When the outdoor dry-bulb temperature is warmer than 55\u00b0F (13\u00b0C) (adjustable [adj.]), the DOAS leaving air dry-bulb temperature (DBTCA) set point shall be 52\u00b0F (11\u00b0C) (adj.). \u2022 When the outdoor dry-bulb temperature is between 45\u00b0F (7\u00b0C) (adj.) and 55\u00b0F (13\u00b0C) (adj.), the DOAS DBTCA set point shall be reset proportionally (see chart) between 52\u00b0F (11\u00b0C) (adj.) and 67\u00b0F (19\u00b0C) (adj.). If DBTOA > 52\u00b0F (11\u00b0C) (adj… <\/td>\n<\/tr>\n | ||||||
| 100<\/td>\n | (b) Figure 5.7 (a) Typical DOAS configuration with (b) supply air temperature reset based on current outdoor air temperature. <\/td>\n<\/tr>\n | ||||||
| 101<\/td>\n | \u2022 When the outdoor dry-bulb temperature is colder than 45\u00b0F (7\u00b0C) (adj.), the DOAS DBTCA set point shall be 67\u00b0F (19\u00b0C) (adj.). \u2022 Activate Reheat Based on Coldest Zones. In this scenario, the building automation system (BAS) monitors the terminal equipment in each zone served by the DOAS unit, and determines if local heat has been activated in any zone (or if the temperatur… Figure 5.8 Reheat activated by coldest zone. This strategy delivers the conditioned outdoor air at a temperature that offsets much of the zone sensible-cooling loads without creating too-low zone temperatures while reducing the need for the zone equipment to operate in heating mode. Of course, … <\/td>\n<\/tr>\n | ||||||
| 102<\/td>\n | The building automation system shall continuously monitor the dry-bulb temperature in all zones served by the DOAS unit. Exclude any zones that are in unoccupied mode. \u2022 When local heating has been activated in at least two (adj.) zones, or if the space temperature is colder than its heating set point \u20131\u00b0F (0.6\u00b0C) (adj.) in at least two (adj.) zones that are not equipped with local heat, the DOAS leaving air … \u2022 When the space temperature in all but one (adj.) zone is warmer than its heating set point +1\u00b0F (0.6\u00b0C) (adj.), the DOAS DBTCA set point shall be reset downward in increments of 1\u00b0F (0.6\u00b0) at a frequency of 10 minutes, until the space tempera… \u2022 The cooling coil leaving temperature shall remain at 52\u00b0F (11\u00b0C) (adj.) as required for dehumidification when the outdoor air temperature is above 52\u00b0F (11\u00b0C) (adj.). Total-Energy Recovery Control <\/td>\n<\/tr>\n | ||||||
| 103<\/td>\n | Figure 5.9 DOAS unit configured with a total-energy wheel and bypass dampers. 1. Full recovery (cooling)\u2014OA conditions exceed the enthalpy\/temperature of the exhaust air (EA). 2. No recovery (cooling)\u2014OA conditions are lower than the enthalpy\/temperature of the EA, but warmer than (or near) the CA set-point temperature. 3. Partial recovery (heating)\u2014OA conditions are lower than the enthalpy\/temperature of EA, and colder than the conditioned air set-point temperature. However, the OA is warm enough that the total-energy wheel can provide all the heat necessary, wit… <\/td>\n<\/tr>\n | ||||||
| 104<\/td>\n | Figure 5-10 Total-energy wheel control modes. Figure 5-11 Total-energy wheel control modes on the psychrometric chart (region A is applicable to enthalpy control). <\/td>\n<\/tr>\n | ||||||
| 105<\/td>\n | 4. Full recovery (heating)\u2014OA conditions are cooler than the CA set-point temperature, and cold enough that even with the total-energy wheel operating at full capacity, some supplemental heating is also required. 5. Frost prevention (heating)\u2014OA conditions are cold enough that frost may be an issue. <\/td>\n<\/tr>\n | ||||||
| 106<\/td>\n | Figure 5.12 Total-energy wheel control on a mild, rainy day. <\/td>\n<\/tr>\n | ||||||
| 108<\/td>\n | Figure 5.13 Total-energy wheel control on a cool, dry day. <\/td>\n<\/tr>\n | ||||||
| 110<\/td>\n | Sensible-Only Heat Exchangers Figure 5.14 Psychrometric chart showing modes of interest for sensible heat exchanger control. <\/td>\n<\/tr>\n | ||||||
| 111<\/td>\n | Total-Energy Recovery <\/td>\n<\/tr>\n | ||||||
| 112<\/td>\n | \u2022 Reduce the Capacity of the Wheel. Modulating a supply-side bypass damper decreases the amount of heat transferred, thereby raising the surface temperature of the device to prevent frost from forming. This approach is often used in climates and ap… \u2022 Preheat the Outdoor (or Exhaust) Air Before it Enters the Wheel. Raising the temperature of the air entering either the supply or exhaust side of the wheel prevents the exhaust air from reaching a condition at which frost might begin to form. Thi… Sensible-Only Heat Exchangers <\/td>\n<\/tr>\n | ||||||
| 113<\/td>\n | Figure 5.15 Demand-controlled ventilation with a DOAS. <\/td>\n<\/tr>\n | ||||||
| 116<\/td>\n | \u2022 Be careful to avoid kinks in pressure tubes extending from the differential building pressure sensor (both outdoor and indoor). \u2022 Use filters ahead of any airflow measurement devices. \u2022 Design for the entire range of operation when planning a building pressurization system, not just maximum airflows. \u2022 Work with architects and engineers to design a tight envelope\u2014it is much easier to pressurize an airtight building, and it will save energy as well. \u2022 If fan speed offset is chosen as a strategy to provide building pressurization, make sure to design and test for the entire range of airflow situations. A fixed fan speed offset is not likely to succeed over a broad range of flows. \u2022 Do not use a duct pressure sensor to measure the building pressure. A whole-building pressure sensor has to be sensitive to very low pressures. \u2022 Use a slow response or timed average sensor reading for controlling the building pressure to avoid unnecessary ramping of the exhaust fan when someone opens or closes a door or otherwise affects the building pressure reading for a short period of… <\/td>\n<\/tr>\n | ||||||
| 120<\/td>\n | Figure 6.1 Well-designed, poorly constructed. <\/td>\n<\/tr>\n | ||||||
| 121<\/td>\n | Submittal Review \u2022 Ensure that air velocity, water velocity, air pressure drop and water pressure drop fall within specified limits (these can vary considerably from standard air- handling unit coil parameters). \u2022 Confirm that both the latent and sensible capacities meet design requirements with 100% outdoor air. \u2022 Verify that performance data has been corrected for the type of antifreeze solution specified. \u2022 For DX cooling coils, confirm that they have sufficient capacity and modulation capability to achieve the required humidity removal at all operating conditions. <\/td>\n<\/tr>\n | ||||||
| 122<\/td>\n | \u2022 Confirm that there is sufficient clearance at the electrical panel. \u2022 Review the location of access doors to ensure that each major component can be easily serviced and\/or removed for cleaning. \u2022 Confirm that the conditioned outdoor air dew point is at (or below) the indoor air dew point during peak outdoor dew-point design conditions. \u2022 Verify that cooling coil traps follow the manufacturer\u2019s guidance for allowing condensate to drain completely out of the drain pan (Figure 6.2). \u2022 Confirm that the manufacturer\u2019s required trap depth can be accommodated by the equipment pad or roof curb. \u2022 If a preexisting trap does not meet specified requirements, a custom trap should be made. \u2022 Confirm that the fan and motor are capable of delivering the required maximum airflow at the specified external and submitted highest internal pressure loss (i.e. dirty filter, wet coil etc.). \u2022 Verify that the type and efficiency of the fans are as required. \u2022 Confirm that the correct types of recovery devices have been submitted. \u2022 Confirm that the effectiveness of each device meets the required effectiveness. \u2022 The pressure drops across the air-to-air recovery devices must be as required or lower. \u2022 Confirm that filters and racks meet the performance criteria specified in the design documents. \u2022 Verify that the pressure drop across filters does not exceed design limits at the conditions specified in the design documents (e.g., clean, midlife, dirty). \u2022 Make sure that filters are located where they can be easily accessed for inspection and replacement. Review the manufacturer\u2019s required clearances and verify that the planned installation provides adequate clearance. \u2022 Bypass dampers must be sized large enough to avoid causing an excessive pressure drop. \u2022 Damper type must be selected to allow for range of control specified in the control sequences. <\/td>\n<\/tr>\n | ||||||
| 123<\/td>\n | \u2022 Verify that controlled devices match the building automation system (BAS) submittal. For example, \u2022 Does the DOAS unit have factory-fitted or field-supplied controllers (or both)? \u2022 Are all BAS-required control points available from the DOAS controller? \u2022 Are there duct smoke detectors on supply and\/or return connections? \u2022 Are motorized dampers provided with the DOAS unit, and will they operate via signals from the BAS? \u2022 If a factory-fitted controller is provided with the DOAS unit, confirm that control points in the BAS submittal match those in the DOAS submittal. \u2022 Ensure that factory controllers share the same protocol as the BAS system (e.g., BACNet\u00ae, LONWorks\u00ae). \u2022 Verify that the DOAS will operate to dry (or heat) any incoming air provided to conditioned spaces, whenever exhaust fans are operating to remove conditioned air from the building. \u2022 Verify that during unoccupied mode, the DOAS will either stop operation or will recirculate and dry the indoor air rather than bringing in humid or cold outdoor air. \u2022 Ensure that comprehensive flow diagrams state the air volume, air dry-bulb temperature and humidity ratio after each component in the system, and that separate flow diagrams are provided for at least three outdoor air entering conditions: peak de… \u2022 Ensure that the capacity required of each component in the system is defined on all three flow diagrams, when operating the stated outdoor air entering conditions. \u2022 Verify that the sum of the building\u2019s exhaust air flows is equaled or exceeded by the sum of the intake air flows from systems that provide conditioned outdoor air or makeup air. \u2022 Verify that all required alarms are communicated from the DOAS unit to the BAS. DOAS units are often located on roofs or other locations that are difficult to access, so visual inspection may occur less frequently than with other equipment. Addit… <\/td>\n<\/tr>\n | ||||||
| 124<\/td>\n | Installation Start-Up Testing <\/td>\n<\/tr>\n | ||||||
| 125<\/td>\n | Figure 6.2 Example of condensate drain trap for a draw-through fan. Test and Balance Verification <\/td>\n<\/tr>\n | ||||||
| 126<\/td>\n | Figure 6.3 Testing and balancing. \u2022 Not enough outdoor air supplied, which can negatively affect IAQ \u2022 Too much outdoor air supplied, which may increase energy use \u2022 Unbalanced outdoor (intake) and exhaust airflows that cause overly positive or negative building pressure, which may negatively affects IAQ, increase energy use, and\/or make entry doors stand open or difficult to open <\/td>\n<\/tr>\n | ||||||
| 127<\/td>\n | System Performance Testing <\/td>\n<\/tr>\n | ||||||
| 128<\/td>\n | Figure 6.4 System performance testing. An engineer and building operator conduct a system performance test. <\/td>\n<\/tr>\n | ||||||
| 129<\/td>\n | Training Figure 6.5 Operators and users training session. Closeout Documentation <\/td>\n<\/tr>\n | ||||||
| 130<\/td>\n | \u2022 DOAS equipment runtime schedules \u2022 Set points for DOAS equipment \u2022 Outdoor air requirements \u2022 Any variations in schedules or set points for different seasons, days of the week, or times of day \u2022 Systems narrative describing the mechanical systems and equipment \u2022 Preventive maintenance plan for the mechanical equipment \u2022 Commissioning program narrative that includes periodic commissioning requirements, ongoing commissioning tasks, and continuous tasks for critical facilities <\/td>\n<\/tr>\n | ||||||
| 132<\/td>\n | Figure 7.1 Filter replacement for rooftop DOAS unit. <\/td>\n<\/tr>\n | ||||||
| 133<\/td>\n | \u2022 All submittal information, testing, adjusting, and balancing (TAB) reports, manufacturer\u2019s operating instructions for major equipment, etc. \u2022 Describing how the systems work, the components included in each system, and how the components will work together. Also summarizes maintenance requirements. \u2022 Construction documents updated to reflect how the system was actually installed. <\/td>\n<\/tr>\n | ||||||
| 134<\/td>\n | \u2022 Include recorded training sessions. \u2022 A description of the purpose of the DOAS in the control sequence, with schematic drawings of the DOAS \u2022 A DOAS training document for operators, which should also be accessible to future operators Recommended Control Points \u2022 General \u2022 Entering outdoor air dry-bulb temperature \u2022 Entering outdoor air humidity \u2022 Fan(s) \u2022 Supply fan status and speed \u2022 Exhaust fan status and speed, if equipped \u2022 Dampers \u2022 Position of dampers \u2022 Cooling \u2022 Leaving coil dry-bulb temperature \u2022 Position of chilled-water coil valve actuator or modulation (or staging) of compressors \u2022 Fault status of each compressor \u2022 Heating \u2022 Leaving coil dry-bulb temperature \u2022 Position of gas valve, hot-water coil valve actuator, or modulation (of staging) of electric heater <\/td>\n<\/tr>\n | ||||||
| 135<\/td>\n | \u2022 Filter(s) \u2022 Differential pressure across filters \u2022 Airflow measurement device(s) \u2022 Total airflow at each sensor \u2022 Energy recovery device \u2022 Entering supply-side dry-bulb temperature (and humidity, if enthalpy recovery) \u2022 Leaving supply-side dry-bulb temperature (and humidity, if enthalpy recovery) \u2022 Entering exhaust-side dry-bulb temperature (and humidity, if enthalpy recovery) \u2022 Leaving exhaust-side dry-bulb temperature \u2022 Control points for any actuators\/speed control associated with the energy recovery device \u2022 Wraparound heat exchanger (if used) \u2022 Leaving upstream-side dry-bulb temperature \u2022 Leaving downstream-side dry-bulb temperature Monitoring \u2022 Ventilation. Verify that the unit provides the correct amount of outdoor air as defined in the construction documents. \u2022 Dehumidification. Verify that the leaving air humidity ratio (or dew point) is as specified, and that space humidity levels fall in the acceptable range. \u2022 Air-to-Air Energy Recovery. Verify that outdoor and exhaust airflows are as specified, and that the effectiveness of the recovery device meets design\/installation expectations. Confirm that the bypass function of the energy recovery device is per… Air Quality Maintenance \u2022 Inspect and change filters on a regular interval (monthly, or as needed to maintain desired collection efficiency). Make sure filters fit tightly and do not bypass air, as this will cause downstream components to become dirty. <\/td>\n<\/tr>\n | ||||||
| 136<\/td>\n | \u2022 Confirm that the following components are clean: \u2022 Cooling coils and drain pans should be inspected to make sure there is no visible biological growth or fouling. \u2022 Air-to-air energy recovery devices on both the exhaust side and supply side should be inspected to make sure all openings are clear and free of obstructions. \u2022 Heating coils should be unobstructed. \u2022 Fans should not have accumulated dust. \u2022 Control components should not be covered or plugged by dust. \u2022 Grease bearings as necessary. <\/td>\n<\/tr>\n | ||||||
| 137<\/td>\n | Figure 7.2 Trends showing high humidity levels in dormitory residential suite. (a) (b) Figure 7.3 Airflow measurement device (a) before and (b) after cleaning. <\/td>\n<\/tr>\n | ||||||
| 150<\/td>\n | AHRI. 2013. AHRI Standard 1060. Standard for performance rating of air-to-air exchangers for energy recovery ventilation equipment. Arlington, VA: Air- Conditioning, Heating, and Refrigeration Institute. AHRI. 2016. AHRI Standard 920-2016. Performance rating of DX dedicated outdoor air system units. Arlington, VA: Air-Conditioning, Heating, and Refrigeration Institute. Ahmed, R., and J. Appelhoff. 2013. Frost-protection measures in energy recuperation with multiple counterflow heat exchangers. REHVA Journal: October. ASHRAE. 2013a. ASHRAE handbook\u2014Fundamentals. Atlanta: ASHRAE. ASHRAE. 2013b. ASHRAE Standard 84. Method of testing air-to-air heat\/ energy exchangers. Atlanta: ASHRAE ASHRAE. 2014. Standard 90.1-2013 user\u2019s manual. Atlanta: ASHRAE. ASHRAE. 2015a. ASHRAE handbook\u2014HVAC applications. Atlanta: ASHRAE ASHRAE. 2015b. Guideline 13. Specifying building automation systems. Atlanta: ASHRAE. ASHRAE. 2016a. ANSI\/ASHRAE Standard 62.1-2016. Ventilation for acceptable indoor air quality. Atlanta: ASHRAE. ASHRAE. 2016b. ANSI\/ASHRAE\/IES Standard 90.1-2016. Energy standard for buildings except low-rise residential buildings. Atlanta: ASHRAE. ASHRAE. 2016c ASHRAE handbook\u2014HVAC systems and equipment. Atlanta: ASHRAE. ASHRAE. 2016d. Standard 62.1 user’s manual. Atlanta: ASHRAE. Crocker, S., and P. Smith. 2013. Service clinic: Servicing desiccant system enthalpy wheels. ContractingBusiness.com. http:\/\/contractingbusiness.com\/ service\/service-clinic-servicing-desiccant-system-enthalpy-wheels. Crowther, H., and Y. Ma. 2016. Design considerations for dedicated OA aystems. ASHRAE Journal: March. <\/td>\n<\/tr>\n | ||||||
| 151<\/td>\n | Fisk, W.J. 2000. Health and productivity gains from better indoor environments and their relationship with building energy efficiency. Annual Review of Energy and the Environment 25:537. Harriman, L.G., D. Plager, and D. Kosar. 1997. Dehumidification and cooling loads from ventilation air. ASHRAE Journal: November. Harriman, L.G., J. Lstiburek, and R. Kittler. 2000. Improving humidity control for commercial buildings. ASHRAE Journal: November. Harriman, L.G., G. Brundrett, and R. Kittler. 2001. Humidity control design guide for commercial and institutional buildings. Atlanta: ASHRAE. Harriman, L.G., and J.W. Lstiburek. 2009. The ASHRAE guide for buildings in hot and humid climates. Atlanta: ASHRAE. ICC. 2012. International energy conservation code. Washington, D.C.: International Code Council. ICC. 2015. International mechanical code. Washington, D.C.: International Code Council. IEA. 2017. Building energy efficiency policies database (BEEP). Paris: International Energy Agency. https:\/\/www.iea.org\/beep\/. Jeong J., and S. Mumma. 2007. Binary enthalpy wheel humidification control in dedicated outdoor air systems. ASHRAE Transactions 113(2). Kosar, D., M. Witte, D. Shirey, and R. Hedrick. 1998. Dehumidification issues of Standard 62-1989. ASHRAE Journal: March. Kumar, S., and W.J. Fisk. 2002. IEQ and the impact on employee sick leave. ASHRAE Journal: July. Mumma, S. 2001. Dedicated outdoor air-dual wheel system control requirements. ASHRAE Transactions 107(1). Mumma, S. 2005a. Role of economizers in DOAS: Part 1. ASHRAE IAQ Applications, Fall 2005. Mumma, S. 2005b. Tempering cold outdoor air. ASHRAE IAQ Applications, Summer 2005. Mumma, S. 2006. Role of economizers in DOAS: Part 2. ASHRAE IAQ Applications, Winter 2006. Mumma, S. 2008. DOAS supply air conditions. ASHRAE IEQ Applications, Spring 2008. Mumma, S. 2009. Contaminant transport and filtration issues with DOAS. ASHRAE Transactions 115. Mumma, S. 2010. DOAS and building pressurization. ASHRAE Journal: August. Mumma, S. 2011. Pros and cons of operating a DOAS EW continuously. Presented at the ASHRAE Annual Conference, Montreal. Mumma, S. 2014. DOAS short course. University Park, PA: Penn State University. Mumma, S. T. McGinn, and J. Murphy. 2013. Dedicated outdoor air systems. ASHRAE Webcast, edited for publication by Sustainable Engineering Group, LLC. <\/td>\n<\/tr>\n | ||||||
| 152<\/td>\n | Murphy, J. 2006. Smart dedicated outdoor air systems. ASHRAE Journal: July. Murphy, J. 2008. Resetting the dedicated OA system leaving-air temperature setpoint. Slide presentation. Personal communication. Murphy, J. 2012. Total energy wheel control in a dedicated OA system. ASHRAE Journal: March. Murphy, J., and B. Bradley. 2009. Air-to-air energy recovery in HVAC systems. La Crosse, WI: Trane. NREL. 2003. Laboratories for the 21st century: Best practices. Golden, CO: National Renewable Energy Laboratory, Persily, A., J. Gorfain, and G. Brunner. 2005. Ventilation design and performance in U.S. office buildings. ASHRAE Journal: April. Phillips, E.G., R.E. Chant, B.C. Bradley, and D.R. Fisher. 1989a. A model to compare freezing control strategies for residential air-to-air heat recovery ventilators. ASHRAE Transactions 95. Phillips, E.G., R.E. Chant, D.R. Fisher, and B.C. Bradley. 1989b. Comparison of freezing control strategies for residential air-to-air heat recovery ventilators. ASHRAE Transactions 95. Quinnell, J. 2016. Improving energy recovery in Minnesota C&I buildings. Energy Design Conference, Conservation Applied Research and Development Presentation, Center for Energy and Environment, Minneapolis. http:\/\/ www.duluthenergydesign.com\/Content\/… Rubel, F., and M. Kottek. 2010. Observed and projected climate shifts 1901\u20132100 depicted by world maps of the Koppen-Geiger climate classification. Meteorologische Zeitschrift 19: 135. Smart Contractor Products. 2015. Weather guards. www.smarthvacproducts.com\/ product\/weather-guards. Stanke, D. 2002. Minimum outdoor airflow using the IAQ procedure. ASHRAE Journal: June. Stanke, D. 2005. Single-path multiple-zone system design. ASHRAE Journal: January. Taylor, S., and C. Cheng. 2010. Economizer high limit controls and why enthalpy economizers don\u2019t work. ASHRAE Journal: November. USGBC. 2013. LEED reference guide for building design and construction. Washington, DC: U.S. Green Building Council. WHO. 2016. Global urban ambient air pollution database. Geneva: World Health Organization. http:\/\/www.who.int\/phe\/health_topics\/outdoorair\/databases\/ cities\/en\/. <\/td>\n<\/tr>\n<\/table>\n","protected":false},"excerpt":{"rendered":" ASHRAE Design Guide for Dedicated Outdoor Air Systems (DOAS)<\/b><\/p>\n |