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fatfallenleafElectronics - Devices

Nov 15, 2013 (4 years and 8 months ago)


Heating, Ventilating,
and Air Conditioning

Donald Fournier

Adjunct Professor

Dept of Urban & Regional Planning

University of Illinois

Heating and Cooling

Space Conditioning:
~40% of building
energy consumption.

Most of the US has
both heating and
cooling demand over
a normal year.

Quantify using
Heating and Cooling
degree days.

Boilers / Furnaces


Used to heat water

either for space heating, providing
domestic hot water or both.


Directly heat the air.

Use boilers in larger structures, furnaces in small structures. Old
boilers generate steam, now hot water.

Combustion gases are separated from heating medium.





Condensing Boilers

Hydrogen in fossil fuels is converted to water by
combustion using significant amounts of the fuel energy.

Condensing the vapor, and reducing flue gases to a
lower temperature can get us higher efficiencies.

Higher Heating Value vs. Lower Heating Value

Issues with doing so:

More Expensive.

Capture and manage condensate (corrosive).

Needs a larger heat

Flue gases may be corrosive and do not disperse as easily.

But condensing boilers can have an AFUE of as much
as 92% whereas non
condensing units have an AFUE
of at most 78%.

Condensing Boiler


Electric Heating

Electricity is an expensive heat source.

Embedded in each kWh of electricity is another two kWh
of heat rejected at the power plant.

Building electrical systems provide heat as a by
(lighting, computing, & plug loads).

Older buildings from c. 1950 may utilize electric heating,
due to low first cost and anticipating of cheap electricity
pricing (used to have special low rates).

Electric Heating may be viable if used as a backup for
more efficient systems or to avoid significantly large fuel

small space heaters that allow for
significantly lower overall space temperatures.

Space Heating

Three main ways to provide heat:

Direct air heating via a furnace.

Radiant Heating (electrical or hot water) using
radiators or baseboards

generally located near

Indirect heating of supply air through an air handler
and a terminal unit.

Well designed systems should heat occupants
and maintain comfort without excessive losses.

Radiation Systems

Terminal units either radiators or perimeter
heating convectors.

Steam radiators offer poor control.

Water radiators can use temperature reset to
control the load. Either may have self
contained thermostatic control valves.

May also have in
floor or in
ceiling radiant
heating (tubes placed in the concrete).

Radiant Systems

Tubing and Manifold

Electric Radiant Heating

Hydronic Baseboards



Moving (Pumping) Heat

While electricity is expensive for direct heating, it can be much
more effectively used to move heat.

Normal application

refrigeration, cooling.

A/Cs reject heat outside to a higher temperature.

Heat pumps do the same thing in reverse.

Electricity used to move heat is added to this.


Performance worsens as temperature gradient
increases, i.e. when coldest.

Average COPs of 2.5
3, Best case ~6

Absorption Cooling

Generally limited to large
industrial / commercial

Not very efficient (COP=<1).

Use ammonia/hydrogen or
salt water as refrigerants.

Cooling still happens during
the evaporation cycle.

Absorption phase equivalent
to vapor

Heat used to evaporate.

Compression Cycles

Use Refrigerants

generally HCFCs to transport heat.

Compress and condense the refrigerant to release heat

high pressure

Expand and evaporate refrigerant to absorb heat

Generally electrically driven but can also be run with steam.

Exchanging Heat

Heat Exchangers are used to transfer or
recover heat instead of rejecting it (wasting it).

Lots of types / designs

wheels, shell and
tube, plates, & heat pipes.

Cooling Towers

Evaporate water to cool

either air or water.

Power Plant / Chiller Heat Rejection.

Cools to wet
bulb temperature; no compressor needed.

EER / SEER, COP and tons

Lots of ways to assess energy efficiency of cooling

Simplest is COP

Ratio of Heat moved to work done.

Next is EER

Energy Efficiency Ratio

Cooling in BTU /
Electric Use in Watt hours (Mixed Units!).


EER = 3.41 * COP.


Seasonally Adjusted EER.

Why? Non
uniform load operation with different seasonal


SEER = EER + 1 to 2

1 ton cooling = 12,000 Btu/

of cooling

Window A/C

Smallest, least efficient

units are window units.

Have low efficiency

May be worthwhile if only a
small amount of the space
needs to be conditioned.

Generally SEER 9.7
(Energy Star is 10.8)

System Units

Next level up.

Minimum SEER 13 required (30% more efficient
than window units) Can get up to SEER 23.

Isolation, improved components, lower noise.

Condensing unit often on the


Rooftop Unit (RTU)

based unit

uses ducts.

Large Chiller Systems

Chilled Water based heat distribution

Campus has five chiller plants that
serve a large loop system

Utility of large systems

most chillers
have a narrow range where they
operate at peak efficiency. Can step
through individual chillers.

Larger systems allow for more efficient
cooling towers, and heat recovery

In general, reciprocating chillers can
serve the smallest
are the most flexible, and

chillers are most

when fully loaded.

Steam Turbine

York Centrifugal Chiller

Temperature and Humidity Control

Humans have a narrow comfort range for
both temperature and humidity

Ventilation / IAQ


remove stale air, high in CO
, & air contaminants.

Outside air is unconditioned

needs to be heated or cooled,
have moisture added or removed.

At the campus

1cfm of ventilated air per year

ANSI/ASHRAE guidance for CO

1000 ppm (IDPH also).

Need to filter air as well.



Forced Air systems

Ducts, generally in plenum spaces


Larger systems have separate supply and return
fans to move (force) air.

Constant Volume Reheat Syst.

Constant Air Volume

Most older systems at the University
are this type.

A constant volume of air is delivered to a space (with a
variable amount of ventilation).

Supply air for the space is cooled and dehumidified to a fixed
temperature (e.g. 55 degrees)

Air is then RE
HEATED to the necessary temperature for
appropriately cooling/heating the space (cold and warm air
can also be mixed)

Fan operates at the design speed all the time.

Temperature reset or on
off control (small systems) to prevent
simultaneous heating and cooling

Constant Volume System

Dual Duct Constant Volume Syst.

Variable Air Volume

Variable Air Volume

newer standard system.

Heating or cooling provided by varying the volume of
conditioned supply air sent to the space.

Air is heated or cooled to a fixed temperature and a
varying amount is provided to that space

Amount of air adjusted by a damper

Minimum level of air provided to meet ventilation

Variable speed fan used.

Reheat is added to the

perimeter zones.

VAV Reheat System

Displacement and Under
Air Distribution

These ventilation systems provide
conditioned air at floor level and allow for
natural convection to lift stale air away from
occupants and toward the return air registers.

Especially useful in high
ceiling rooms and
atria where the entire space does
not need conditioning.

Can use under
floor plenums
for air distribution.



Control Systems

HVAC Control systems can use dozens of inputs

temperature (interior/exterior), humidity,
occupancy, CO2 levels, schedules, & electricity

Must control motors, fans, dampers, furnaces,
blowers, transducers, actuators …

Initial systems were pneumatic

simplified control using compressed air.

Now HVAC controls are computerized

Digital Control. Even web

Building Automation Systems


Computerized, Intelligent System. Controls Mechanical
and Lighting Systems, Monitors performance, and warns of
system failures

Next Steps

Next class we will cover energy conservation
in existing buildings.

We’ll take a look at these various systems
and discuss how to make them more
efficiency and use less energy.