Chapter 11: DESCRIPTION OF HVAC SYSTEMS

Chapter 11: DESCRIPTION OF HVAC SYSTEMS
Agami Reddy (rev-May 2017) Photos Recap: Building loads, human comfort and ventilation Basic HVAC components The complete system with HX loops Classification of HVAC systems Single zone systems for residences (split and packaged) Single zone and multi-zone systems for large buildings Central plant systems for campus buildings Condensers General classification of secondary systems Examples of all-air and air-water systems HVAC&R design considerations HCB 3-Chap 11: HVAC Systems Description

HCB 3-Chap 11: HVAC Systems Description

Large OLD Building in New York City, Oct 2011 Older buildings had very obtrusive and ugly HVAC equipment – Roofs had to be reinforced to structurally support them Water tanks Cooling tower HCB 3-Chap 11: HVAC Systems Description

Packaged rooftop units supplying conditioned air to different apartments HCB 3-Chap 11: HVAC Systems Description

RECAP HCB 3-Chap 11: HVAC Systems Description From Kolderup, 2009

LOAD CALCULATIONS Design Conditions
Location specific tables are available for Outdoor Design Conditions: DBT and WBT, Solar Indoor Design Conditions: DBT and RH Energy Calculations Energy consumed over season or whole year Need climatic data (such as TMY3) HCB 3-Chap 11: HVAC Systems Description

From Kolderup, 2009 HCB 3-Chap 11: HVAC Systems Description

ASHRAE Comfort Chart Valid for: Sedentary or slightly active person Summer: light slacks & Short sleeve shirt (0.5 clo) Winter: Heavy slacks,long sleeve & sweater or jacket (1.0 clo) Air motion: < 30 ft/min in winter < 50 ft/min in summer No direct solar or other radiation incident on body HCB 3-Chap 11: HVAC Systems Description

ASHRAE Standard 62 HCB 3-Chap 11: HVAC Systems Description

0.3 HCB 3-Chap 11: HVAC Systems Description

Elements of a Building Energy Simulation Program
HCB 3-Chap 11: HVAC Systems Description

Basic Components of a HVAC System
Heating source: adds heat to a fluid Boilers (water or steam); furnaces, chimneys… Cooling source: removes heat from a fluid Chillers, air-conditioners, evaporative coolers.. Distribution system: ducts & pipes to carry fluid (s) Equipment to move fluids: fans, pumps Devices to transfer heat between fluid and air Primary systems Secondary systems HCB 3-Chap 11: HVAC Systems Description

Basic Boiler and Air Conditioner
Fig Basic boiler schematic Fig Components of a vapor compression cycle. HCB 3-Chap 11: HVAC Systems Description

Fig Example of furnaces for residential space heating: vertical. HCB 3-Chap 11: HVAC Systems Description

The complete system with HX loops Fig Complete sketch of an all-air secondary system with a water cooled primary system showing some of the important components. Note that the five heat transfer loops needed to remove the heat gains to the space. As the space loads get smaller, some of these loops can be combined or eliminated. HCB 3-Chap 11: HVAC Systems Description

Fig Two types of hydronic terminal units: (a) old-fashioned cast-iron radiator and (b) the fan coil unit Fig Schematic of zone terminal box and room air flows Ducted return and plenum return HCB 3-Chap 11: HVAC Systems Description

Classification of HVAC Systems
One way is based on size, construction, and operating characteristics: Unitary or packaged Central or built-up Campus or district Packaged Roof-top AHU Room Air Conditioner Chiller HCB 3-Chap 11: HVAC Systems Description

Single zone systems for residences Fig. 11.6 Typical residential heating system – all air - Here the HVAC is quite simple: a furnace provides heating in the winter and an air-conditioning unit provides cooling in the summer. - Just about the only required maintenance is the annual replacement of the furnace filter and an occasional inspection of the air conditioning unit. - Occupants of many houses pay almost no attention to these systems (until something goes wrong) HCB 3-Chap 11: HVAC Systems Description

Fig Layout of a hydronic system with terminal heaters in each room. A series piping layout is shown though other types of layouts (such as parallel or series-parallel) are also common. HCB 3-Chap 11: HVAC Systems Description

Fig. 11.8(a) Split A/C system for a central air system for residential and small commercial buildings HCB 3-Chap 11: HVAC Systems Description

Fig (b). Photograph showing the numerous air cooled condensers of various sizes (except for two water cooling towers in the forefront) which take up most of the roof space of tall apartment buildings in cities HCB 3-Chap 11: HVAC Systems Description

Packaged Rooftop Unit (single zone large spaces)
Fig Assembled view of a packaged roof top unit Fig Sketch of a roof top unit showing individual Components and air flows HCB 3-Chap 11: HVAC Systems Description

Multi-zone: Larger buildings need to be zoned to maintain comfort
Zone: A room or group of rooms in which comfortable conditions can be maintained by a single controlling device - Similar thermal disturbance (weather, solar, internal) - Share one set of Sensor, Controller, AC system HCB 3-Chap 11: HVAC Systems Description

Fig Large AHU Fig Typical commercial building HVAC system components There are many more components to the HVAC system. Major equipment groups: A mechanical room in the basement: boiler, chiller, and central air-handling unit. - A series of pipes and ductwork for distributing conditioned water and air to the distribution system - Terminal boxes within the spaces Fig Cooling plant with three large centrifugal chillers HCB 3-Chap 11: HVAC Systems Description

Example of Diurnal Electric Profile of a Building kW HCB 3-Chap 11: HVAC Systems Description

Example of Relative Contribution of Cooling Plant Sub-systems HCB 3-Chap 11: HVAC Systems Description

Central Plants Fig Basic water distribution loop for a campus HCB 3-Chap 11: HVAC Systems Description

Condensers Fig Air-cooled condenser HCB 3-Chap 11: HVAC Systems Description

Fig Mechanical draft cooling tower (Courtesy of O’Neal and Bryant, 2001) HCB 3-Chap 11: HVAC Systems Description

Fig Induced draft cooling tower system (four separate towers are shown) HCB 3-Chap 11: HVAC Systems Description

Importance of HVAC&R for Green or Low-Energy Buildings
Secondary systems and primary equipment are much more critical in terms of energy efficiency than envelope features in non-residential buildings These sub-systems are undergoing a lot of innovation! All the more need to understand the basic scientific principles Study of HVAC systems is complex because of: - numerous components - large variety of HVAC systems for different building types - variable operating conditions (diurnal and seasonal) HCB 3-Chap 11: HVAC Systems Description

General Classification of HVAC Secondary Systems
All-water systems fan coil, unit ventilator All-air systems single zone, reheat systems, VAV, dual- duct, … Air-water systems or hybrid systems induction, reheat (water), heat pump systems chilled beam, underfloor, DOAS HCB 3-Chap 11: HVAC Systems Description

All-air Central Systems: CAV and VAV Supply air meets both building loads and ventilation loads- VAV system modulates air supply flow rate depending on load in each room- supply temperature remains constant One of the most widely used energy efficient system- used widely in office buildings,…. Heat/cooling from primary equipment transferred to air thru coils HCB 3-Chap 11: HVAC Systems Description

All Air Systems Fig Pneumatic actuator on outdoor air dampers Fig Single duct AHU HCB 3-Chap 11: HVAC Systems Description

Fig Heat recovery device HCB 3-Chap 11: HVAC Systems Description

Common Type of Air-Water System Closed-Loop Water Source Heat Pump 1/2
System has separate loops for: - conditioning fresh or outdoor air - meeting heating/cooling building loads terminal unit supplies both heat and cool HCB 3-Chap 11: HVAC Systems Description

Closed-Loop Water Source Heat Pump 2/2
Outdoor air brought in to meet ventilation needs- This air needs to be conditioned- Requires its own heating and cooling equipment Inside the rooms Terminal box Plan view HCB 3-Chap 11: HVAC Systems Description

Design and Operation Design- first cost: selecting equipment (furnace, air-conditioners,..) which can keep occupants comfortable Operation – over life of system: running expenses (electricity, gas, maintenance,…)- design has a large impact on operating costs HCB 3-Chap 11: HVAC Systems Description

HVAC&R System Design Considerations
What type of building (performance requirements)? Climate? Load dynamics (how uniform are the loads from one zone to another)? How precise should indoor environment be controlled? Spatial constraints of HVAC system Where can the system be located? Importance given to first cost, energy consumption, operating costs (Life Cycle Costing)? Simplicity/ Reliability of systems Flexibility (in case building use is changed in the future) Serviceability/ Maintainability Electric and gas price structure Special considerations? HCB 3-Chap 11: HVAC Systems Description

Outcomes Understanding of the importance of nation-wide energy use in buildings Appreciation of the fact that HVAC systems on buildings can be very obtrusive Review of thermal comfort, building loads and ventilation calculations Knowledge of some of the basic components of HVAC systems Understanding of the several heat transfer loops needed to condition a space Understanding of the three different generic HVAC system types Knowledge of some of the generic HVAC systems and their functioning Knowledge of the different types of condensers Understanding of the three different generic classes of secondary systems Understanding the functioning of some all-air and air-water systems Familiarity with the numerous considerations dictating HVAC&R design selection HCB 3-Chap 11: HVAC Systems Description

Chapter 11: DESCRIPTION OF HVAC SYSTEMS

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Chapter 11: DESCRIPTION OF HVAC SYSTEMS

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