HVAC DISTRIBUTION and DELIVERY SYSTEMS (Part 1) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 1 REMINDER HVAC = Heating, Ventilating, Air-Conditioning The AC part of HVAC implies a system that can provide simultaneous control of Air temperature Air relative humidity Air distribution Air quality AC systems may be local, central, or district in scale and come in many, many configurations local systems were addressed previously (unitary and split systems); district systems are multi-building implementations of central systems Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 2 1
Reminder: HVAC System Functional Parts Source components (provide heat/coolth; may include chiller, boiler, furnace, cooling tower, etc.) Distribution components (transfer heating/cooling effect from source to zones; include ductwork, piping, etc.) Delivery components (introduce heating/cooling effect into zones; include diffusers, radiators, convectors, fan-coils, radiant panels, etc.) Controls (for comfort, efficiency, safety; include thermostats, valves, dampers, smoke detectors, pressurestats, etc.) source components tend to be large, but hidden; distribution can be voluminous, but is often concealed; delivery components are typically small but located within occupied spaces; controls are generally small and unobtrusive Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 3 Reminder: Central HVAC System Types Three primary system classifications: All-air systems Air-water systems All-water systems Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 4 2
Defining Central HVAC Types ask: what distribution elements must enter a zone to provide climate control? if only a duct = all-air? plenum if only a pipe = all-water if a duct and a pipe = air-water? zone room Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 5 Basic Central HVAC System Sub-types HVAC All-Air local central district Single zone Terminal reheat Multi-zone Dual-duct Variable air volume Hybrids (mixing aspects of the above) single zone term reheat multi-zone dual duct VAV hybrids all-air air-water all-water Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 6 3
Basic Central HVAC System Sub-types Air-Water Induction Fan-coil with supplemental air Radiant with supplemental air fairly simple; no diagram necessary Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 7 Basic Central HVAC System Sub-types All-Water Fan coil without supplemental air Radiant heating / cooling It is questionable whether an all-water system can meet the ASHRAE definition of air-conditioning relative to current expectations for control of air quality fairly simple; no diagram necessary Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 8 4
Choosing A Distribution Medium Air vs. Water Specific heat (Btu/lb deg F) 0.244 vs. 1.0 Density (lb/cu ft) 0.075 vs. 62.4 Heat capacity (Btu/cu ft deg F) (0.244)(0.075) = 0.018 (1) (62.4) = 62.4 Ratio (0.018) / (62.4) = 0.0003 (or 3410) distribution medium want list cheap, easy to move, effective, safe x 2* usually x 2* *supply and return Heating, Cooling, Lighting: Lechner Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 9 Choosing A Distribution Medium distribution medium want list functional, easy architectural integration Air vs. Water projection into usable space ^^ << no intrusion into room volume Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 10 5
Thoughts On All-Air Distribution Only air is distributed to the various zones for climate control (no heating/cooling water goes to the zones) Water may be used to convey heat/coolth from sources to central air-handling units (AHU) but not from the AHUs to the zones Various system types (such as VAV) are used to provide control of zone conditions in response to specific project OPR (budget, IAQ, energy, ) All-air is a very common system choice, because There is good potential for acceptable IAQ There is minimal intrusion of equipment into occupied spaces Water leakage and condensate disposal issues are centralized The system might also be used for smoke control (fire protection) Current all-air system design trends include: Dedicated outdoor air systems (DOAS) Underfloor air distribution (UFAD) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 11 Basic All-Air System Types Single zone Terminal reheat Multi-zone (not the same as multiple zone) Dual-duct Variable air volume (VAV) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 12 6
All-Air Single Zone System Simplest type of all-air system Provides constant volume air flow (fan is on or off) Permits only one zone of control (there is one thermostat) Lowest-cost all-air system (due to simplicity) System can heat or it can cool (but it cannot do both simultaneously) Control is exercised at the air-handling unit (via coil modulation) Surprisingly common system (residences, big box, interior zones) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 13 System Components notes: if sa = say 100 cfm, then ra is typically around 90 cfm and oa is around 10 cfm (10% of supply) except under economizer operation (using outdoor air for free cooling); ra is NOT normally below the floor ea ea ahu = air-handling unit; fil = air filter; cc = cooling coil; hc = heating coil; T = thermostat; oa = outdoor air; ra = return air; sa = supply air; ea = exhaust air to maintain pressure balance in the building, a volume of air flow roughly equal to the oa must be exhausted (fans) or relieved (leaked) from the building Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 14 7
Component Functions air-handling unit: condition and circulate air to support comfort/iaq/process air filter: remove some contaminants from air fan: overcome friction to move air through the system cooling coil: sensibly and latently cool air heating coil: sensibly heat air thermostat: control zone air temperature (via in-zone sensor) outdoor air: provide ventilation air to improve IAQ return air: reduce energy use by recycling conditioned air supply air: provide air that can successfully condition zones Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 15 All-Air Single Zone Example refrigeration air handling ductwork source distribution a packaged rooftop single zone HVAC for a residence (refrigeration + air handling in a box ductwork to rooms) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 16 8
All-Air Terminal Reheat System A simple all-air system with terminal control (this gives flexibility) Provides constant volume air flow (fan is on or off) Can provide numerous zones (2, 30, 400, ) with excellent control Relatively low first cost Control is exercised near the zones via the reheat coils (by modulation) Can heat and cool different zones simultaneously (flexibility) Seriously frowned upon or prohibited by energy codes because added heat is used to compensate for overcooling (an example of a system that is very effective and very inefficient) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 17 All-Air Terminal Reheat Example one zone, with multiple (to be installed) diffusers (serving one facade orientation) sa from AHU terminal reheat coil thermostat control is exerted here Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 18 9
All-Air Multi-Zone System md = mixing dampers (combine hot and cold air) >> requires a separate supply air duct for each zone A fairly complex all-air system Provides constant volume air flow (fan is on or off) Can provide multiple zones of control (but around 12 zones is the maximum per AHU due to spatial constraints) Control is exerted at the air-handling unit (zones not easily changed) A moderate-cost system (involves lots of ductwork) Can heat and cool different zones simultaneously Complicated coordination of ducts near AHU because each zone requires a separate supply duct connection Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 19 All-Air Multi-Zone Example 1 2 3 4 showing discharge from multi-zone AHU; the cylinders are pneumatic control damper actuators; four zone ducts can be seen above Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 20 10
All-Air Multi-Zone Example note the center supply duct expanding (to reduce air speed, thus friction and noise); all zone ducts are doing the same essentially scrambling for space Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 21 All-Air Dual-Duct System box controls mixing of hot and cold supply air streams A complex all-air system with terminal control (thus flexible) Provides constant volume air flow (fan is on or off) Can provide numerous zones of control (thus is flexible) A fairly high-first-cost system Can heat and cool different zones simultaneously (thus is flexible) Two supply ducts (one with hot air, one with cold air) run throughout the system (serving a floor or an entire building) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 22 11
All-Air Dual-Duct Example hot and cold supply air ducts flexible ducts connecting to mixing box Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 23 All-Air Dual-Duct Example the two supply ducts are not the same size, because heating/cooling loads and hot/cold supply air delta-t values are not the same Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 24 12
All-Air VAV (Variable Air Volume) System box controls volume of supply air admitted to zone << supplemental heating element A simple all-air system from an equipment perspective A potentially complex system from a control perspective Provides a variable supply air flow (which has several implications) Can provide numerous zones with terminal control (is flexible) Relatively low first- and life-cycle cost (it is energy efficient) Air-supply usually just cools (requiring a supplemental heating system) A very, very common system Numerous VAV box types are available (including reheat) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 25 All-Air VAV Example VAV box to diffusers VAV box from AHU Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 26 13
All-Air VAV Box (with induction) mixed air to diffusers air is pulled in from plenum induction feature allows AHU to supply a variable air quantity (saving energy) while zones see a more-or-less constant airflow Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 27 supply air from AHU VAV Box (with hot water reheat) as an architect you knew this was going to be exposed to view AHU control point no control, yet presented under all-air because system does not reduce size of supply ducts Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 28 14
Lots of Choices (with more to come) Each system presented above has plusses and minuses. If there was a one-size-fits-all system then the others would have disappeared into history. Even terminal reheat, with its abject energy waste, has resurfaced in VAV systems. The correct system choice for a given project depends upon the OPR (which need to be clear and explicit). A demand for low-first-cost will favor a simple system A demand for low-life-cycle-cost will favor an energy-efficient system A demand for energy efficiency will favor a VAV system A demand for close control of pressure relationships (as in a hospital or laboratory) will favor a constant volume system A demand for flexibility will favor a terminal-control system A demand for outstanding IAQ will tend to favor a constant volume system (or a carefully-designed VAV system) A demand for consistent noise will favor a constant volume system Limited space/volume for distribution will favor a single-duct system Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 29 and Lots of Ductwork Choices www.metroheatcool.com metal externally insulated www.salaair.com durkeesox.en.busytrade.com/ www.directindustry.com flex www.boatdesign.net fabric internally lined glass fiber Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 30 www.vacsysint.com 15