Error - LEAM

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

•
Boilers
–

Used to heat water
–

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

•
Furnaces
–

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.


Firetube

Boiler

Watertube

Boiler

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
-
exchanger.

•
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

Furnaces

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
-
product
(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
expenditure
–

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
windows.

•
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

Antique
Radiators

Modern
Radiators

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.

•
Difficulty
–

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
applications.

•
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
-
compression
condensation.

•
Heat used to evaporate.

Vapor
-
Compression Cycles

•
Use Refrigerants
–

generally HCFCs to transport heat.

•
Compress and condense the refrigerant to release heat
–

at
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
systems.

•
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!).

•
Conversion
–

EER = 3.41 * COP.

•
SEER
–

Seasonally Adjusted EER.

•
Why? Non
-
uniform load operation with different seasonal
temperatures
.

•
Conversion
–

SEER = EER + 1 to 2

•
1 ton cooling = 12,000 Btu/
hr

of cooling

Window A/C

•
Smallest, least efficient


units are window units.

•
Have low efficiency
components.

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

•
Generally SEER 9.7
-
9.8
(Energy Star is 10.8)

Split
-
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


roof
–

Rooftop Unit (RTU)

•
Air
-
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
loads
efficiently,
rotary
-
screw
chillers
are the most flexible, and

centrifugal
chillers are most

efficient
when fully loaded.



Steam Turbine
Chiller

York Centrifugal Chiller

Temperature and Humidity Control

•
Humans have a narrow comfort range for
both temperature and humidity

Ventilation / IAQ

•
Ventilation
–

remove stale air, high in CO
2
, & 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
-
$1.

•
ANSI/ASHRAE guidance for CO
2

–

1000 ppm (IDPH also).

•
Need to filter air as well.

2010


Default

Forced Air systems

•
Ducts, generally in plenum spaces
–

above
ceiling.

•
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
requirements.

•
Variable speed fan used.

•
Reheat is added to the


perimeter zones.

VAV Reheat System

Displacement and Under
-
floor
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.

•
Example
–

BIF

Control Systems

•
HVAC Control systems can use dozens of inputs
–

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

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

•
Initial systems were pneumatic
–

highly
simplified control using compressed air.

•
Now HVAC controls are computerized
–

Direct
Digital Control. Even web
-
addressable

Building Automation Systems


BAS
–

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.

ADDITIONAL
QUESTIONS