​Assignment A6

Window AC

Individual Room System

Window units are designed for use in the individual rooms of a building.  For example, multiple window units are used throughout a builing in order to maintain and regulate cooling throughout.  The system operates by circulating warm air from inside the space to outside the space via electricity.  The heat and disposed water from the air are rejected to the atmosphere thus leaving the cooler air inside the space.  This process repeats over and over to keep the space at a specific temperature.  This system can be considered both Primary and Secondary as well as a major system because it functions on its own without the assistance of additional equipiment.

Limitations

• Limited BTU capacity for large spaces.  Well suited for smaller rooms.

• Must be installed on outer envelope of the space.

• Serves as an aesthetic problem due to look and loss of window space.

• Power supply needs can increase operation costs of unit. 

• Short life cycle as compared to larger units. 

Rooftop Package Unit

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A rooftop air-handling package unit (AHU) is designed for larger commercial needs and is normally placed on the roof of a structure.  This unit regulates and circulates air in order to provide heating, cooling, and ventilation.  This system is considered a Primary system, but also has secondary system functionality.  

Limitations

• Initial Costs can be high due to multiple system parts and repairs.

• Operating costs and maintenance can become expensive.

• Life span is not as long due to exposure to the elements.

  • Life span will vary based on climate of outdoor conditions.

• Can be difficult to install in a pre-existing building versus a newly built one. 

• Large Equipment Loads.

  • Supports must be designed to carry large loads.

• Units are only capable of servicing 5-stories at a time.

  • Multiple units may be necessary based on structure height.

• Lack control of temperature to individual spaces.

Combination Home Air Heating and Cooling

Residential/Commercial

This system type uses a combination of heating and cooling principles in order to service the intended space.  It harnesses a combintation of a heat pump system and a vapor compression system.  Through heating and cooling processes the system circulates heated and cooled air throughout the space and can be adjusted accordingly.  This system is considered both Primary and Secondary due to harnessing the same ductwork in order to circulate the air in the space.  

Limitations

• Higher initial costs.

• Efficiency standards must be met for code reasons.

• Unit sizing effects performance of heat pump.

• Operation in colder temperatures causes the pump system to work harder than normal.  

  • Can decrease life span of pump if overused in colder temperatures.

Active Solar HVAC

Residential/Commercial

Active Solar HVAC systems utilize solar energy to heat a fluid.  Some systems can use air, but others use liquid as the primary fluid.  This system requires a secondary system, on top of the primary fluid system, to distribute or store the heated fluid, usually some type of storage tank that provides circulation.  The primary system is a solar collector which is normally found on the top of the structure.  The fluid present on the collector absorbs solar energy and transfers it to the secondary system.  

Collector Types:

• Flat Plate (Most Common)

• Batch (aka Breadbox)

• Evacuated Tubes

Subsystems:

• Circulation 

• Control

• Storage Tank

Limitations

• Climate effects amount of solar energy absorbed.

• Backup systems are necessary.

• Storage tanks must be kept in room termperature locations.

• Tank weight, and potential freezing hazards can be dangerous to the structure they are installed in. 

Radiant Floor Heating

Residential/Commercial

Radiant floor heating is a common system that even though it is not physically visible, the effects of its radiant can be felt by those individual occupying the space.  Heat is supplied through a network of hot-water tubes embedded into the floor system of the space.  Thermal radiation releases from the floor and transfers itself into any objects it is in contact with.  Air temperatures stay relatively constant, but the surrounding surfaces refrain from stealing warmth from the occupant's body, therefore the occupant stays comfortable.  

Advantages

• Better air quality.

• Silent heating system.

• Units are practically invisible.

• Increased comfort level.

• Possible increase in energy efficiency.

Limitations

• Difficult to install to a pre-existing floor.

• Feasible more for if flooring is being replaced or if a home is being built from scratch.  

• Lack of crawl spaces and/or basements can make it difficult/impossible to install this type of system in a home or building.

VAV

Variable Air Volume

Variable Air Volume or VAV is a system that conditions a space by varying the amount of air flow introducted to a space at a constant temperature.  A constant temperature of about 55 degrees Fahrenheit is blown through the system at various rates to condition the space in such a way that gains and losses of the space are kept under control.  

Components:

• Central Cooling Tower

• Boiler System

• Fan Network

• Duct System

• Thermostats

• Diffusers

Advantages

• Precise temperature control.

• Maintains constant supply air temperature.

  • Reduces energy consumed by fans.

  • Lowers building cooling load.

  • Increases life span of system.

• Humidity control.

• Pressure control. 

Limitations

• Maintenance of comfortable temperatures in spaces that require different heating/cooling loads is limited.

Convective Heating

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Convection heating its the transfer of thermal energy  from one space to another through the movement of a fluid.  Convection heaters utilize air convection currents circulating through the body of the appliance and across its heating element.  This newly heated air, with increased volume, becomes bouyant and rises into, and heats the space.  

Advantages

• Low operational noise.

• Effective to heat small spaces.

• Easy to install & have low proflies.

• Various size and shapes of units.

Limitations

• Inefficient in heating large open spaces.

• Unit is susceptible to overheating.

• Due to heat from unit rising directly to ceiling, large energy loss is common.

• Objects near unit can cause blockage of air/heat flow and damage to objects. 

  • Potential fire hazards.

Chilled Beam

Chilled beams utilize convection to heat or cool a space in a large building.  Beams can be suspended from the ceiling of the space or integrated into the spaced internal structure.  Cool water is allowed to flow through the beam system and in turn "chills" the air surrounding the beam.  This air then sinks to the floor, which allows the warmer air to rise up and repeat the cycle.  Chilled beams are considered a secondary system type.

Types:

• Active

• Passive

Limitations

• Cannot remove particulates from the surrounding air.

• Condensation is a constant issue that requires a separate system to be controlled.

• Small heating capabilities.

• New building system.

  • Needs more exposure to become a more commonly used system.

• Occupy significant ceiling space.

  • Coordination with other systems of the space are necessary.

Geothermal Heat Pump

Geothermal heating systems can be integrated into both commercial and residential buildings.  This system type is an effective alternative to most traditional systems due to its ability to provide heating and cooling at a siginificantly lower price.  No large outdoor equipment, and very practical for its purpose.  

Limitations

• Refrigerants for the system can be expensive to maintain and resupply.  

• Water, which is the safest fluid to use in the system, does not transfer heating and cooling loads as well as refrigerant fluids.

• Materials to construct piping system can be costly.

• Design and construction costs can be expensive due to invasiveness of the systems design.  

• Not many contractors are specialized in installing/designing/maintaining this type of system. 

Hot Water Radiators

Residential

Found commonly in residential homes, hot water radiators provide heating to homes of various sizes.  The Primary system consists of a boiler powered by a gas or an oil that heats the water for the system.  The Secondary subsystems are made up of the individual piping, circulation pump, radiators, and an expansion tank.  These secondary systems connect together and allow the heat within the system to flow throughout the space.  The heat is distributed throughout the residential space via baseboard radiators or stand alone radiators.

Limitations

• Less suitable for large building due to time needed for heat to travel through system.

• Excess amounts of electricity are needed to run the cicrulation pumps and can become costly to keep running. 

• Maintenance can be an issue with older systems.  

High Temperature Radiant Heating

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High temperature radiant heating systems heat the room or space by radiant energy.  Units are normally mounted to the ceiling of the space and allow heat to be radiated throughout the space.  Commonly found in warehouses, air hangars, and high bay facilities.  

Advantages

• Energy Savings

  • Lower thermostat set points.

  • Less heat loss through loading doors.

  • Reduced fan energy consumption.

• Social Benefits

  • Increased occupant comfort.

• Guiding Principles

  • Optimize energy performance (Energy Efficiency)

• Associated LEED Credits

Limitations

• Cost & Temperature Issues for Residential Housing

  • Need for constant heating in residential housing is not always necessary.

  • Can become costly.

• Safety Issue

  • High surface temperatures can cause injury or damage to goods.  Hence why units are normally placed high on the ceiling of the space.

CAV

Constant Air Volume

Constant Air Volume (CAV) is a simple system in which the flow rate of supply air is constant, but with varying temperature.  This is done to meet the thermal loads of the occupied space.  This system is normally small and serves single thermal zones, but with the right variations they can be applied to larger buildings.  

Types:

• Single Duct

• Mixed Air

Limitations:

• Inefficient Use of Energy

• Affects the efficiency of the system when it supplies the same air flow rate when a slower flow rate would be sufficient.

• Oversized Ducts

  • Causes increase in design cost as well as higher chances of air leakage during distribution.

• Limited Temperature Control for Single Ducts

• Need for Additional System

Passive Solar

Trombe Wall

A passive solar, Trombe wall system is one that continuously absorbs heat from the sun during the day and then radiates it to the indoor space during the night when temperatures drop.  Trombe walls are made of high thermal materials with a vent at the top and bottom to circulate warm air.  

Components:

• Aperture (Collector)

• Absorber

• Thermal Mass

• Distribution Control

Advantages

• ​Cost free heating after installation.

• Uses existing wall spaces.

• Simple and relatively effective.

• Positive health effects.

• Provides humidity control.

• Enhances thermal comfort.

Limitations

• Costly to install.

• Complicated design.

• Low thermal resistance.

• Heat gain is unpredictable.

• Overheating can be a problem.

• Must follow specific energy codes.

  • Limitations on amount of allowed glass.

• Can only be controlled by closable vents.