03 Classification HVAC

THERMAL THERMAL COMFOR COMFORT T AND A ND INDOOR INDOOR CL CL IMATE Lecture: - CLASS CLA SSIF IFIC ICA A TI TION ON OF HVA HVA C SYS SYSTE TEMS MS

 Assist. Prof. Igor BALEN BALEN

International MSc Programme Sustainable Energy Engineering

Why HVAC system? - heat and mass transfer between indoors indoors and outdoors not controlable by passive means → Thermal Comfort indoors cannot be achieved - very strict IAQ requirements requirements (operating theaters, chip chip production, production, ...) - natural natural ventilatio ventilation n not posible/res posible/restricte tricted d •

traffic noise

•

large/deep rooms

•

high wi wind-induced pre pres ssure di differences

Why HVAC system? - heat and mass transfer between indoors indoors and outdoors not controlable by passive means → Thermal Comfort indoors cannot be achieved - very strict IAQ requirements requirements (operating theaters, chip chip production, production, ...) - natural natural ventilatio ventilation n not posible/res posible/restricte tricted d •

traffic noise

•

large/deep rooms

•

high wi wind-induced pre pres ssure di differences

Operation principles Drain Pain •Removes moisture condensed from air stream

Cooling coil •Heat transfer from air to cooling medium •Extended surface coil

Evaporator Condenser Expansion valve Compressor Controls

Operation principles

Heating coil •Heat transfer from heating medi medium um to air  Heat pump (condenser) Furnace Boiler Electric resistance Controls

Operation principles

Blower •Overcom  pressure d of system

Adds heat to stream

Makes noise

Performs di rently at di conditions (a flow and pre drop)

Operation principles

Duct syste (piping for hydronic systems) •Distribute conditioned air  •Remove a from space

Provides ventilation Makes noise

Affects comf

Affects indoo air quality

Operation principles

Diffuser •Distribu condition air withi room

Provides ventilation

Makes noi

Affects com

Affects IA

Operation principles Dampers •Change airflow amounts

Controls outside air fraction Affects building safety

Operation principles Filter •Removes  pollutants •Protects equipment

Imposes substantial pressure drop Requires maintenance

Operation principles Controls •Makes everything work  Temperature Pressure (drop) Air velocity Volumetric flow Relative humidity Enthalpy Electrical Current Electrical cost Fault detection

HVAC system basic classification 1. Low-velocity (low-pressure) - air flow velocity in ducts 2-8 (10) m/s - pressure drop in ducts (external) 500-2000Pa - ducts usually in rectangular shape; sides ratio 1:2 to 1:4,5 - comfort applications: hotels, theaters, museums, concert halls... 2. High-velocity (high-pressure)

- air flow velocity in ducts 10-30 m/s - pressure drop in ducts (external) 1500-3500Pa - ducts usually in round shape - applications: bussiness/office buildings, buildings with limited space placing of the ducts ...

HVAC system typology - Three generic types of HVAC systems: • All-air system • Air-water system • All-water system

HVAC system typology 1. All-air system - low-velocity - high-velocity Unitary

Single duct

Dual duct - warm air duct - cold air duct

- single-package - split

Variable Air Volume (VAV)

Constant Air Volume (CAV)

Single zone

Variable Air Volume (VAV)

Multiple zone - with zone reheat coils - with zone AHU

Constant Air Volume (CAV)

HVAC system typology 2. Air-water  - low-velocity - high-velocity With zone Induction units heating/cooling coils

Two-pipe SUPPLY+RETURN

With changeover between hot and

Fan coil units

Three-pipe HSUP+CSUP RET common

Without changeover 

Radiant heating/cooling

Four-pipe HSUP+HRET CSUP+CRET

Valve control one exchanger 

Damper control two exchangers

Unitary air conditioners

- consist of one or more factory-made assemblies that normally inclu evaporator or cooling coil and a compressor and condenser combina - heating and cooling function, ventilation

- air-source unitary heat pump consisting of one or more factory-ma assemblies, which normally include an indoor conditioning coil, compressor(s), and an outdoor coil → must provide a heating function possibly a cooling function as well.

- water-source heat pump is a factory-made assembly that rejects o extracts heat to and from a water loop instead of from ambient air. - split system is a unitary air conditioner or heat pump having more one factory-made assembly (e.g., indoor and outdoor units)

Unitary air conditioners Rooftop HVAC system (single-package)

- limited to five or six floors because duct space and available blower power become excessive in taller buildings.

Unitary air conditioners  Air-/water-sourced heat pump • single-package reverse-cycle system for both heating and cooling • single source of energy can supply both heating and cooling requirements • heat output can be as much as two to four times that of the purchased (electric) energy input (in kWh). • vents and/or chimneys may be eliminated

Unitary air conditioners Individual room air-conditioning system

Unitary air conditioners Split system

- different types: - mono-split, multi-split, CRV, VRV - new multi-split VRV with up to 50 indoor units connected to one ou

Central HVAC systems

- equipment room for a central system is normally located outside th conditioned area - in a basement, penthouse, service area, or adjac or remote from the building → require space at a central location and potentially large distribution system

- larger air-handling equipment is usually custom-designed and fabric to suit a particular application

- most of the components are available from many manufacturers completely assembled or in subassembled sections that can be bolte together in the field - specific design parameter must be evaluated to balance cost, controllability, operating expense, maintenance, noise, and space - close year-round control of temperature and humidity are possible

 All-air systems Central single-duct, single-zone, constant air volume

-common duct distribution system at a common air temperature feeds terminal apparatus (diffusers) - one controlled space with one thermostat that maintains a set point

 All-air systems Central single-duct, multiple-zone, constant air volume

- zone temperature or zone supply volume flow rate is controlled by terminals - reheat coils are used to control the temperature and/or relative humi

 All-air systems Central single-duct, multiple-zone, constant air volume - system with zone air-handling units (AHU)

 All-air systems Central single-duct, variable air volume

- controls temperature in a space by varying the quantity of supply ai than varying the supply air temperature - VAV terminal unit at the zone varies the quantity of supply air to the - supply air temperature is held relatively constant: while supply air temperature can be moderately reset depending on the season, it mu always be low enough to meet the cooling load in the most demandi zone and to maintain appropriate humidity - greatest energy saving associated with VAV occurs at the perimeter zones, where variations in solar load and outside temperature allow th supply air quantity to be reduced - potential problems with minimum outdoor air supply (increasing CO concentration) and humidity control, where particular care should be t in areas where the sensible heat ratio (ratio of sensible heat to sensib plus latent heat to be removed) is low, such as in conference rooms

 All-air systems Central single-duct, variable air volume

 All-air systems Variable air volume (VAV) box

- VAV box or a cooling VAV box is a terminal device in which the supp volume flow rate is modulated by varying the opening of the air passa means of a single-blade butterfly damper  - pneumatic or direct digital control (DDC) of a damper  - minimum supply air rate ≥30% of design flow rate

 All-air systems Central dual-duct, constant air volume

 All-air systems Central dual-duct, variable air volume

 All-air systems Central dual-duct, variable air volume

- terminal units that function like a single-duct VAV cooling terminal u and a single-duct VAV heating terminal unit in one physical pack

 All-air systems Dual-duct VAV box and operating chart

 All-air systems  Advantages:

• The location of the central mechanical room for major equipment al operation and maintenance to be performed in unoccupied areas. In addition, it allows the maximum range of choices of filtration equipme vibration and noise control, and the selection of high quality and dura equipment.

• Keeping piping, electrical equipment, wiring, filters, and vibration an noise-producing equipment away from the conditioned area minimize service needs and reduces potential harm to occupants, furnishings, processes.

• These systems offer the greatest potential for use of outside air for  economizer cooling instead of mechanical refrigeration for cooling.

• Seasonal changeover is simple and adapts readily to automatic con

 All-air systems  Advantages (continued): • A wide choice of zoning, flexibility, and humidity control under all operating conditions is possible, with the availability of simultaneous heating and cooling even during off-season periods. • Air-to-air and other heat recovery may be readily incorporated.

• They permit good design flexibility for optimum air distribution, draft control, and adaptability to varying local requirements.

• The systems are well suited to applications requiring unusual exhau makeup air quantities (negative or positive pressurization, etc.). • All-air systems adapt well to winter humidification.

• By increasing the air change rate and using high-quality controls, possible for these systems to maintain the closest operating condition ±0.15 K dry bulb and ±0.5% rh. Today, some systems can maintain

 All-air systems Disadvantages: • They require additional duct clearance, which reduces usable floor and increases the height of the building.

• Depending on layout, larger floor plans are necessary to allow enou space for the vertical shafts required for air distribution.

• Ensuring accessible terminal devices requires close cooperation be architectural, mechanical, and structural designers. • Air balancing, particularly on large systems, can be more difficult.

• Perimeter heating is not always available to provide temporary heat during construction.

 Air-water systems

Central primary air, high-velocity system (induction units) or low-veloc system (fan coils)

 Air-water systems Central primary air, with fan coils

 Air-water systems Central primary air and fan coils, separated

 Air-water systems  Advantages: • Individual room temperature control allows the adjustment of each thermostat for a different temperature at relatively low cost.

• Separate heating and cooling sources in the primary air and second water give the occupant a choice of heating or cooling.

• Less space is required for the distribution system when the air supp reduced by using secondary water for cooling and high velocity air. return air duct is smaller and can sometimes be eliminated or combin with the return air system for other areas, such as the interior spaces • The size of the central air-handling apparatus is smaller than that air system because little air must be conditioned.

• Dehumidification, filtration, and humidification are performed in a ce location remote from conditioned spaces.

 Air-water systems  Advantages (continued):

• Ventilation air supply is positive and may accommodate recommend outside air quantities.

• Space can be heated without operating the air system via the secon water system. Nighttime fan operation is avoided in an unoccupied building. Emergency power for heating, if required, is much lower tha most all-air systems.

• Components are long-lasting. Room terminals operated dry have anticipated life of 15 to 25 years. The piping and ductwork longevity equal that of the building. Individual induction units do not contain fan motors, or compressors. Routine service is generally limited to temperature controls, cleaning of lint screens, and infrequent cleanin the induction nozzles.

 Air-water systems Disadvantages: • For most buildings, these systems are limited to perimeter space; separate systems are required for other areas. • More controls are needed than for many all-air systems.

• Secondary airflow can cause the induction unit coils to become dirty enough to affect performance. Lint screens used to protect these term require frequent in-room maintenance and reduce unit thermal performance.

• The primary air supply usually is constant with no provision for shut This is a disadvantage in residential applications, where tenants or room guests may prefer to turn off the air conditioning, or where management may desire to do so to reduce operating expense. • A low primary chilled water temperature is needed to control space humidity adequately.

 Air-water systems Disadvantages (continued):

• The system is not appropriate for spaces with high exhaust requirem (e.g., research laboratories) unless supplementary ventilation air is provided.

• Central dehumidification eliminates condensation on the secondary heat transfer surface under maximum design latent load. However, abnormal moisture sources (e.g., from open windows or people congregating) can cause condensation that can have annoying or damaging results.

• Energy consumption for induction systems is higher than for most systems due to the increased power required by the primary air press drop in the terminal units. • The initial cost for a four-pipe induction system is greater than for all-air systems.

 All-water systems Chilled water systems Two-pipe constant flow

Two-pipe constant flow with primary loop

Two-pipe constant flow with secondary loops

 All-water systems Four-pipe fan coils - separate hot and cold supply and return piping - heating and cooling possible in different rooms at the same time

Induction unit

- centrally conditioned primary air is supplied to the unit plenum at medium to high pressure - medium- to high-velocity air flows through the induction nozzles an induces secondary air from the room through the secondary coil - secondary air is either heated or cooled at the coil, depending on season and the room requirement

Fan coil Supply Air

Fan

Cooling Coil Heating Coil Filter Ventilation Air

Drain pan - heat, cool, move air by force convection through the condit space, filter the circulating air introduce outside ventilation a available in many configurat

Special systems Dehumidification heat pump

Special systems

 All-water heat pump with thermal storage and optional solar collector

Special systems System with indirect evaporative cooling

EXHAUST

RETURN OUTSIDE

SUPPLY

Special systems System with dessicant rotary wheel