* Some of the images used in these slides are taken
from the internet for instructional purposes only
Building Energy Systems
- HVAC: Heating, Distribution -
Bryan Eisenhower
Associate Director
Center for Energy Efficient Design
Researcher and Lecturer
Department of Mechanical Engineering
UCSB
Winter 2015
HVAC
Cooling:
 (Natural Ventilation)
 Refrigeration cycles
 Absorption cycles
 Evaporation
Heating:
 (Natural through envelope – solar, internal gains)
 Boilers (water / steam)
 Furnaces
 Electric
 Refrigeration
 Natural – solar collector
** These subjects cover how to create cooling/heating, distribution comes later
Boilers
 Exchanges heat from combusted fuel (oil, gas,
wood, coal, elec., etc.) with water
 If water boils – steam
 If water does not boil – hot water (still called a
boiler)
 A specification of the boiler is its steam pressure
 A boiler needs combustion air but this air does not
circulate through the building, water or steam is sent
to the building
 The capacity of the boiler signifies how much heat it
can produce
 The efficiency of the boiler depends on how much
load is on the boiler, the part load ratio (0-1) defines
whether the boiler is off or at full capacity
 The hot water or steam is taken to the building and
exchanged with the zone
 Steam systems are typically more expensive to
install because they work at higher pressures
 Water systems have less losses because their
temperatures are lower
http://www.lenntech.com
Furnaces
 Air is forced over a combustion
chamber or electric heater
 The burners operate on different
combustibles (e.g. oil, gas)
 Return: Cool air is taken from the
zones/house (through a filter) and
mixed with fresh outdoor air
 Supply: Warm air is distributed
throughout the building
 Combustion exhaust goes up through
the roof
 Heat exchanger design and variable
fan speed influence system
efficiencies
 Condensing furnace: High efficiency
furnaces extract so much heat from
the air that water vapor condenses
utilizing the latent heat
http://www.onehourairconditioningcharlotte.com
Electric heating
 The combustion processes can be
replaced with electric elements (much
like inside an electric oven)
 Benefits are cheaper equipment,
good efficiency for all loads, no
exhaust
 Disadvantage: electricity costs
usually much more than gas costs
 Remember that electricity needs to
be created at a plant (using gas, oil,
coal) and then transported to your
building
 Generation and transmission losses
make electric heating less desired
 On-site renewable electric generation
could change this (wind, solar,…)
http://www.warmair.com
http://www.energyvanguard.com
Electric vs. Gas
Gas
~ 90% efficient, cleaner than coal
Electric
~ 25% efficient, higher emissions due
to coal burning
http://www.centerpointenergy.com/
Service water
 The hot water generated from the
boiler is not suited for human
consumption
 Different standards are made for heat
exchangers that are used for drinking
etc.
 Hot service water is sometimes
included in described HVAC
equipment
 These hot water heaters are similar
to what you have in your house, with
a few other variations possible
http://www.allstar-hvac.com
Solar Collectors
 Plenty of free heat can be gained through absorption in the envelope or
through windows
 Solar thermal collectors are devices that collect solar heat and bring it into the
building through HVAC equipment
 Just like regular windows, a solar panel collector has optical properties that
limit the amount of heat gained
 Additionally, since a hot liquid (often water) is running through tubes on the
roof, heat transfer occurs between the tubes and ambient, reducing the
efficiency as this temperature difference increases
SDH
www.daviddarling.info
Solar Collectors
Flat plate
Contains about 40 gallons of water about
enough for one persons residential needs
Evacuated tube
More efficient at higher temperature
differentials (e.g. very cold out)
Parabolic
Often need to angled directly at sun, don’t
pick up diffuse radiation
Evacuated tube
www.sunmaxxsolar.com
wikipedia
Flat plate collector
solartribune.com
www.gvskills.com
HVAC
Occupied
area
Past
Air
Distribution
Earth
Now
Secondary
Systems
Past
Primary
Systems
EnergyPlus documentation
Distribution Units (water)
 Cooling / Heating can also be brought into
the building directly, without the air flow
 Different methods:
 High temperature steam
 Mid temperature hydronic (floor,
baseboard)
 High temperature electric
 Quiet, no particulates, heat usually touches
body directly (e.g. feet)
 Don’t get fresh air
 Up to 50% of the heat transfer is actually
convection
Underfloor heating
http://sandiumblog.blogspot.com
Hydronic Radiator
Steam Radiator
http://homerepair.about.com
Radiant cooling
http://www.mothering.com
http://www.dbrothers.com
http://wiki.aia.org
Distribution Units (water)
Fan coil units:
 Fan and heating/cooling coil (heat
exchanger) in one unit
 Installed in occupied space which
means no ducting needed
 Economical install but fan noise may be
a problem
fanupdate.blogspot.com
www.qualityairservices.com
Thermal Storage:
 Can store cooling in thermal mass of the
building or in chilled water / ice
 Can store up to a million pounds of ice
that is created at night, used during the
day
 Optimization possibilities are when to
make the stored energy and how much
www.lti-ast.co.uk
Single Duct Reheat
 Preheating/cooling at the AHU is performed to maintain the coldest supply
temperature for the entire building
 Zones that don’t need this cold air will reheat it
 Optimization potential: what is the coldest air that is necessary?
Chilled water loop
Exhaust
Return Air
Reheat
Air Handling Unit (AHU)
Outdoor Air
Supply Air
•
•
•
•
Economizer
Fan
Filter
Cooling / Heating Coils
Preheat / Precool
Hot water loop
Distribution Units (Air)
 The cooling needs of each zone in a building
may be different (e.g. the computer lab vs. the
library vs. the kitchen)
 Single duct systems:
 The cooling of the air in the AHU may be
just enough for some zones but too much
for others.
 To account for this, the air is cooled
enough for all zones and reheated for the
zones that don’t need that much cooling
 Dual duct systems
 Dual duct systems combine just enough
cold and hot air to maintain comfort in
each zone
 Note there are many smaller variations
including fans/dampers in the terminal boxes,
electric reheat, etc.
Single duct VAV reheat
Hot water
http://www.automation.com
Dual duct mixing box
http://www.nailor.eu
http://www.energybooks.com
Single Duct Reheat
 Preheating/cooling at the AHU is performed to maintain the coldest supply
temperature for the entire building
 Zones that don’t need this cold air will reheat it
 Optimization potential: what is the coldest air that is necessary?
Chilled water loop
Exhaust
Return Air
Reheat
Air Handling Unit (AHU)
Outdoor Air
Supply Air
•
•
•
•
Economizer
Fan
Filter
Cooling / Heating Coils
Preheat / Precool
Hot water loop
Single Duct Reheat
 Variants:
 Direct expansion for the AHU, electric preheat or reheat, some combination of the
all?
Exhaust
Return Air
Electric
Reheat
Air Handling Unit (AHU)
Outdoor Air
Supply Air
•
•
•
•
Economizer
Fan
Filter
Cooling / Heating Coils
Direct expansion
Preheat / Precool
Dual Duct
 Preheating/cooling at the AHU is performed to generate two supply temperatures
 Each zone mixes these flows as needed
 Optimization potential: what are the two temperatures of the supply ducts?
Chilled water loop
Exhaust
Return Air
Mixing Box
/
/
/
/
/
/
Air Handling Unit (AHU)
Outdoor Air
Hot Deck
Supply
Cold DeckAir
Preheat / Precool
Hot water loop
/
Economizer
Fan
Filter
Cooling / Heating Coils
/
•
•
•
•
Summary of a few different types of Heating and cooling layouts
There are a large number of possibilities to cool/heat a building
given all the different components available.
Air
 Typical chiller configurations
 Pictured is a vapor compression chiller,
the diagram is similar for absorption
chillers
Air-cooled
Heat to Atmosphere
Evaporative
Cooling Tower
Liquid
Heat to Atmosphere
Condenser
Refrigerant
Liquid-cooled
Air
Chillers
Expansion
Condenser
Refrigerant
Compressor
Expansion
Evaporator
Evaporator
Energy
added
Energy
added
Radiant panel, AHU
cooling coil, fan
coil unit
Radiant panel, AHU
cooling coil, fan
coil unit
Air
Liquid
Air
Liquid
Compressor
Heat from building
Heat from building
 Heat pumps can be configured in many
ways
 Two ways are shown below, but these
can be partially interchanged (e.g. airto-liquid)
Air
Air-to-air
Liquid-to-Liquid
Air
Heat Pumps (cooling)
Heat to Earth
Ground, lake,
etc.
Liquid
Condenser
Refrigerant
Heat to Atmosphere
Expansion
Refrigerant
Compressor
Condenser
Evaporator
Compressor
Evaporator
Air
Energy
added
Heat from building
Liquid
Radiant panel, AHU
cooling coil, fan
coil unit
Air
Expansion
Energy
added
Heat from building
Heat Pumps (heating)
 Heat pumps can be configured in many
ways
 Two ways are shown below, but these
can be partially interchanged (e.g. airto-liquid)
Air-to-air
Liquid-to-Liquid
Heat from Earth
Ground, lake,
etc.
Liquid
Condenser
Refrigerant
Heat from Atmosphere
Expansion
Refrigerant
Compressor
Condenser
Evaporator
Expansion
Compressor
Evaporator
Energy
added
Heat to building
Energy
added
Liquid
Radiant panel, AHU
heating coil, fan
coil unit
Heat to building
Heating
Boiler
Liquid,
steam
Furnace
Radiator, AHU
heating coil, fan
coil unit
Air
Air
Heat to building
Heat to building
Implementing in OS
Two high level approaches to Heating and Cooling implementation
1) Ideal air loads: Systems and plant is not modeled, cooling and heating
come from the district
2) System and plant modeling: many different choices to implement
different system components and plant
Ideal Loads
System Modelling
Open Studio HVAC systems
The online tutorial is a very addendum to this lecture:
http://openstudio.nrel.gov/sketchup-plug-tutorials
Open Studio HVAC systems
Two main ways to implement
HVAC
 Terminal units only (e.g. no
plant, just energy that is
needed in the zone)
 Entire plant and terminal
units
Outdoors
Fresh Air
Hot Water
Chilled water
Refrigerant
Cooling Tower
Controllers
Thermal Zone
Terminal units only
Terminal Units Only
 For each zone, select
 Ideal loads ‘off’, drag the PTHP from the
‘library’ to the HVAC system
 Thermostat ‘on’, drag clgstp, htgstp to the
cooling and heating thermostat schedules
 Do this for all 5 zones
Open Studio HVAC systems
Detailed system w/plant:
To insert a new HVAC
system, go to the HVAC tab
on the left and push the green
+ symbol to add a system.
Air Loop
The General Idea:
Unoccupied
area (roof,
basement,
outside)
Inside
You can
add zones
here, this
wont be
done on
all slides
but it is
implied….
Plant Loop
The General Idea:
When you add air
loop components
that need a plant,
OpenStudio will
add a plant loop as
necessary
Open Studio HVAC Templates
Packaged rooftop unit
Fresh air intake
and exhaust
DX – Direct expansion cooling (no
water involved, expansion of
refrigerant cools air)
Gas fired heat
Constant
speed fan
Open Studio HVAC Templates
Packaged rooftop heatpump
Heat pump provides heating or
cooling. Supply air fan built into
this sub-model
Open Studio HVAC Templates
Packaged DX rooftop VAV with reheat
Cooling is same as ‘Packaged rooftop
unit’.
Initial heating provided from either steam
or hot water from plant
Variable
speed fan
Reheat is from plant
Damper controls flowrate
Open Studio HVAC Templates
Packaged Rooftop VAV with Parallel Fan Power Boxes and Reheat
Cooling and heating same as
‘Packaged rooftop unit’
Variable
speed fan
Reheat is from plant
Damper, fan controls flowrate
Open Studio HVAC Templates
Packaged Rooftop VAV with Reheat
Cooling and heating both from plant
Varibable
speed fan
Reheat is from plant
Damper controls flowrate
Open Studio HVAC Templates
VAV with Parallel Fan-Powered Boxes and Reheat
Variable
speed fan
Open Studio HVAC Templates
Warm Air Furnace Gas Fired
Warm Air Furnace Electric
Heat with either
a gas or
electric furnace
Constant
speed fan
UCSB Buildings
A number of mechanical schedules have been uploaded to the website.
You will need to implement the Air Handling Units only, using VAV reheat
Adding fan coil units and other heating/cooling devices is optional and/or
may be requested for the final.