Mediterranean Commercial Important Species

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Ball State Architecture | ENVIRONMENTAL SYSTEMS 2 | Grondzik 1

HVAC DISTRIBUTIONand DELIVERY

SYSTEMS


REMINDERS

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

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Reminder: HVAC System Functional Parts

Source components (provide heat/coolth; chiller, boiler, furnace, cooling tower, etc.)

Distribution components (transfer heating/cooling effect from source to zones; ductwork, piping, etc.)

Delivery components (introduce heating/cooling effect into zones; diffusers, radiators, convectors, fan-coils, radiant panels, etc.)

Controls (for comfort, efficiency, safety; 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 within occupied spaces; controls are generally small and behind the scenes


Reminder: Central HVAC System Types

Three primary system classifications:

All-air systemsAir-water systemsAll-water systems

and there are some hard-to-categorize systems (such as interconnected heat pumps)

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Defining Central HVAC Types

What enters the zone to provide climate control?

If only a duct= all-air

If only a pipe= all-water

If a duct and a pipe

= air-waterroom

plenum

zone


Basic Central HVAC System Sub-types

All-Air

Single zone

Terminal reheat

Multi-zone

Dual-duct

Variable air volume

Hybrids (mixing aspects of the above)

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Basic Central HVAC System Sub-types (cont’d)

Air-Water

Induction

Fan-coil with supplemental air

Radiant with supplemental air


Basic Central HVAC System Sub-types (cont’d)

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

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Choosing ADistribution Medium

Air vs. WaterSpecific 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 3,410)

x 2*

usually x 2*

*supply and return

Heating, Cooling, Lighting: Lechner

“want list” –cheap,easy to move,effective,safe


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 is often used to convey heat/coolth from sources to central air-handling units – but not to the zones

• Various system types (such as VAV) are used to deal with various project contexts

• 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 “hot” all-air design trends include

• Dedicated outdoor air systems (DOA)• Underfloor air distribution (UFAD)

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Basic All-Air System Types

• Single zone

• Terminal reheat

• Multi-zone (not the same as “multiple” zone)

• Dual-duct

• Variable air volume (VAV)


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• Surprisingly common system (residences, big box, interior zones)

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System Components

ahu = air-handling unit; fil = air filter; cc = cooling coil; hc = heating coil;

T = thermostat;

oa = outdoor air; ra = return air; sa = supply air

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

to maintain pressure balance in the building, a volume of air flow equal to the oa must be exhausted or relieved from the building


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 conditions (via temperature sensing)

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

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All-Air Single Zone Example

a packaged rooftop single zone HVAC for a residence

refrigeration air handling ductwork

distributionsource


All-Air Terminal Reheat System

• A simple all-air system with terminal control (this adds flexibility)• Provides constant volume air flow (fan is on or off)• Can provide numerous zones (2, 30, 400, …) with good control• Relatively low first cost• Can heat and cool zones simultaneously (this adds 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)

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All-Air Terminal Reheat

Example

terminal reheat coil—thermostat control is exerted here

one zone,

with multiple (future) diffusers

(serving one facade orientation)


All-Air Multi-Zone System

• 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)• Control is exerted at the air-handling unit (zones not easily changed)• A moderate-cost system (involves lots of ductwork)• Can heat and cool zones simultaneously• Complicated coordination of ducts near AHU because each zone

requires a separate supply duct connection

md = mixing dampers(combining hot and cold air) >>

requires a separatesupply air ductfor each zone

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All-Air Multi-Zone Example

showing discharge from multi-zone AHU; cylinders are pneumatic control damper actuators; four zone ducts can be seen above

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All-Air Multi-Zone Example

note the center supply duct expanding (to reduce friction and noise); all zone ducts are doing the same–essentially scrambling for space

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All-Air Dual-Duct System

• 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 zones simultaneously (thus is flexible)• Two supply ducts (one with hot air, one with cold air) run

throughout the system (an entire building, or a floor or two)

box controls mixingof hot and coldsupply air streams


All-Air Dual-Duct Example

hot and cold supply air ducts

flexible ducts connecting to

mixing box

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All-AirDual-Duct Example

the two supply ducts are not the same size,because heating/cooling loads and hot/coldsupply air delta-t values are not the same


All-Air VAV (Variable Air Volume) System

• 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 provided numerous zones with terminal control (is flexible)• Relatively low first- and life-cycle cost (it is energy efficient)• Air-side usually just cools (requiring a supplemental heating system)• A very, very common system• Numerous VAV box types are available (including reheat)

box controls volumeof supply air admitted to zone

<< supplementalheating element

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All-Air VAV Example

VAV box

todiffusers

VAV box

from AHU


All-Air VAV Box (with induction)

air is pulled in from plenum

SA from AHU

mixed air to diffusers

induction feature allows AHU to supply a variable air quantity (saving energy) while zones see a more or less constant airflow

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VAV Box (with hot water reheat)

no control, yetcontrol point

if you knew this was going to be exposed to view …

AHU

presented under “all-air” because system does not reduce size of supply ducts


Lots of Choices (with more to come)

Each system presented above has plusses and minuses. If there were 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 design intents and criteria (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 (as in a hospital or lab) 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

Mediterranean Commercial Important Species

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