Displacement Ventilation ECO DV logo Displacement Ventilation Systems Presented by Randy Zimmerman - Chief Engineer HVAC Product Design, Development and Application ASHRAE TC 2.6 and TC 5.3 AHRI Engineering and Section Committees BSME – Texas Tech University 1983 LEED Green Associate ashraelogo Displacement Ventilation Systems Question and Answer Panel Randy Zimmerman - Chief Engineer Jim Aswegan – Chief Engineer James Gray – Product Manager ECO DV logo Displacement Ventilation Systems Agenda Basic System Concepts Displacement Diffusers Applications Product Demonstrations So Many Choices There’s a Good, Better and Best System for Every Building Old and New Technology Overhead Air Distribution Underfloor Air Distribution Active Chilled Beams Displacement Ventilation Conventional Overhead Air Distribution Displacement Ventilation Supply air 63 - 68oF Cool air supply displaces warm room air at low velocities Uses the natural buoyancy of warm air to provide improved ventilation and comfort Cold air moves slowly across the floor until it reaches a heat source, then rises Person, computer, etc Basic System Concepts Return Air Outlet located at ceiling level Allows heat from ceiling lights to be returned before it is able to mix with occupied zone Reduced supply volume means higher return temperatures Humidity Issues A potential problem with warmer supply air temperatures is higher humidity Supply system must reduce relative humidity to less than 60% to meet IAQ concerns Condenser water reheat, run-around coils, or face & bypass Use of a separate system to dry outside air or the use of desiccant dehumidification If 55oF supply air is used for dehumidification, return air can be mixed with supply air to achieve 65oF air Chapter 20 (ASHRAE, 2009) System Performance Evaluation and Guidelines for Displacement Ventilation (ASHRAE, 2003) Displacement Ventilation in Non-Industrial Premises (REHVA, 2002) Fundamentals HVAC Applications System Performance for DV REHVA DV Guide Displacement Ventilation Application Guide office equipment, Qoe (Btu/h) Heat generated by overhead lighting, Ql (Btu/h) Heat from the exterior wall and window surfaces including transmitted solar radiation, Qex (Btu/h) Weighting Factors (per ASHRAE RP-949) Occupants, desk lamps and office equipment, аoe = 0.295 Overhead lighting, аl = 0.132 Exterior wall/window surfaces including transmitted solar radiation, аex = 0.185 Calculating the Heat Transfer The heat transfer to the region of interest can therefore be calculated by the following equation: ∆ThfρCpV = аoeQoe + аlQl + аexQex Where: ∆Thf = temperature differential between the head and foot level of occupant (°F) ρ = air density under standard conditions (lb/ft3) Cp = specific heat of air at constant pressure (Btu/lb-°F) V = supply flow rate (ft3/h) Simplifying the Equation Since V = nHA Where: n = the required air change rate (ach) H = space height (ft) A = floor area (ft2) The heat transfer equation can be simplified to ∆Thf = (аoeQoe + аlQl + аexQex ) / (ρCpnHA) Thermal Comfort ASHRAE Standard 55 – Thermal Environmental Conditions for ashraelogo 55-2010 More Calculations The same equation can be used to calculate the required ventilation rate: n = (аoeQoe + аlQl + аexQex ) / (ΔThf ρCpHA) The cooling air volume (cfm), Vh, for a typical office environment can then be calculated using the following equation: Vh = nAH/60 Substituting the ventilation rate, n, into the equation yields: Vh = (0.295Qoe + 0.132Ql + 0.185Qex)/(ΔThf ρCp) °F (for a seated occupant) ρ = 0.075 lb/ft2 Cp = 0.24 Btu/lb-°F This equation can be simplified to: Vh = 0.076Qoe + 0.034Ql + 0.048Qex This equation is very useful for typical applications involving seated occupants. Displacement Ventilation Advantages Reduced cooling power for desired room temperature in the occupied area Improved air quality in occupied area Longer periods of free cooling Displacement Ventilation Smoke Test requirements to deliver air = fan energy savings Cost of Pressure Calculation Tool on Titus Website www.titus-hvac.com/software/onlinetools Fan Energy Savings with Displacement Ceiling diffusers: 24” x 24”, 10” inlet Displacement diffuser: 24” x 79”, 10” inlet ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality Zone Air Distribution Effectiveness, Ez Best Overhead System = 1.0 Displacement Ventilation = 1.2 16.7% Less Fresh Air Required ashraelogo 62 Improved Ventilation contaminants are not redistributed throughout the room Displacement Ventilation Overhead System 207 Difference Dallas 55 °F = 107 Days: 65 °F = 177 Days: 70 Difference Chicago 55 °F = 209 Days: 65 °F = 263 Days: 54 Difference (based on average daily temperatures) Displacement Ventilation & LEED Optimize Energy Performance: EAp2 Increased Ventilation: IEQc2 Thermal Comfort Design: IEQc7.1 ECO DV logo IEQc2 Thermal Comfort Design: IEQc7.1 ECO DV logo Obstructive furniture or partitions Don’t use with mixed air devices The adjacent zone *More about this in a minute from the device Adjacent zone > 50 fpm Stationary occupants should not be located in the adjacent zone Bild2 Adjacent Zone Diffuser design Plenum Mounting Frame Perforated baffle or pattern controller Front Cover Perforated Displacement Diffusers Pattern Controller Design Metal Louver vertical Iso 2 COSMOSFloXpress_snap1 Displacement Diffusers left Split pattern (right & left) Bild2 Displacement Diffusers Displacement Diffusers Standard adjacent zone from factory Modified adjacent zone after adjusting pattern controllers to change pattern Lobbies Restaurants and Casinos Theaters and Auditoriums Classrooms and Meeting Rooms Airports and Train Stations Museums and Public Spaces Application Examples Airports and Train Stations Museums and Public Spaces Application Examples Contaminants are heavier than air (chloramine) In combination with mixing systems Application Examples Where: Qoe = Heat generated by occupants, desk lamps and office equipment (Btu/h) Ql = Heat generated by overhead lighting (Btu/h) Qex = Heat from the exterior wall and window surfaces including transmitted solar radiation (Btu/h) surfaces including transmitted solar radiation (Btu/h) W Where: A = floor area (ft2) L = room length (ft) W = room width (ft) Design Procedure Step 3 – Calculate the Cooling Air Volume, Vh Vh = 0.076Qoe + 0.034Ql + 0.048Qex Where: Qoe = Heat generated by occupants, desk lamps and office equipment (Btu/h) Ql = Heat generated by overhead lighting (Btu/h) Qex = Heat from the exterior wall and window surfaces including transmitted solar radiation (Btu/h) Outdoor Airflow, Voz Vbz = (Rp x Pz) + (Ra x Az) Where: Rp = people outdoor air rate from ASHRAE 62.1 Table 6-1 (cfm/person) Pz = zone population (#) Ra = area outdoor air rate from ASHRAE 62.1 Table 6-1 (cfm/ft2) Az = zone floor area (ft2) Voz = Vbz / Ez Where: Ez = 1.2 from ASHRAE 62.1 Table 6-2 Design Procedure Step 5 – Determine the Supply Air Volume, V Will be larger of either the cooling air volume, Vh, or the zone outdoor airflow requirement, Voz. Step 6 – Calculate the Supply Air Temperature, Ts Ts = Tsp – 3.6 – ((AQt)/(2.33V2 + 1.8 AV)) Where: Tsp = room temperature (°F) ((Qt)/(1.08V)) Step 8 – Select Supply Diffuser(s) Designed to blend well with the architecture of a building Various shapes Rectangular units can be mounted in walls Circular and semicircular units can be installed into columns Displacement Diffusers CFM Accessories Duct Cover 59660 2,400 CFM Accessories Duct Cover Mounting base 60277 Displacement Diffusers 2,400 CFM Accessories Duct Cover Mounting base Displacement Diffusers 59644 Displacement Diffusers Rectangular – Curved Face Flush or floor mount 3–way pattern Max Airflow: 1800 CFM Accessories Duct cover Mounting base Rectangular – “Stair Riser” Steps, Stair Risers applications 1–way pattern Max airflow: 380 CFM Great for auditoriums, concert arenas, and lecture halls Displacement Diffusers 59660 Displacement Diffusers Circular Column or floor mount 360° discharge Max Airflow: 2500 CFM Accessories Duct cover Mounting base 59645 Displacement Diffusers Semi-Circular 180° Sidewall or column applications 180° pattern Max Airflow: 3700 CFM Accessories Duct cover Mounting base Displacement Diffusers U - shaped Semi-circular w straight sides 3–way pattern Max Airflow: 3700 CFM Accessories Duct cover Mounting base 59646 Displacement Diffusers Corner w/ Curved Face Corner mount applications 2–way pattern Max Airflow: 1200 CFM Accessories Duct cover Mounting base 59661 Displacement Diffusers Corner with Flat Face Corner mount applications 2–way pattern Max Airflow: 1200 CFM Accessories Duct cover Mounting base What About Heating? Perimeter heating can not be accomplished with traditional displacement ventilation Separate system required in most applications: Fin tube products Ducting of hot or reheated air Radiant panels Underwindow fan coils Displacement cooling Mixed-air heating Actuated diverter (24V) Air flows up to 1,400 CFM Used in California Public Schools… Dual chamber plenum Displacement diffuser – cooling Linear diffuser – heating