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Unformatted text preview: Options being considered:
– Better Heater = 93% efficient, or
– Better Wall = R-12 (U = 0.47 W/m2-K)
(Note: Based on our equation for , either option
reduces heating energy by ≈14%.) Very simple space heating system:
Heated Space fuel fuelfired
heater = 0.47 # ⁄$% ∙ ℃ = 100 $% = 80% ( − )
= • In assessing which option is better, let’s consider
how the heating system will be sized by the
Usually, one of the first steps in designing a heating
system is to perform a heat loss calculation to
determine the “peak load” (i.e. determine how
much heat must be provided to maintain the space
temperature during the coldest expected weather.) Equipment sizing for simplified example…
Ti = 21°C To
Note: For this example,
we’ll assume the room has
only one heat loss path. wall area
A = 100 m2 Design outdoor air temperature for the location is -19°C. = ( − ) Answer: For R-10 (U = 0.55 W/m2-K), = 2.20 kW For R-12 (U = 0.47 W/m2-K), = 1.88 kW And with 25% oversizing-factor (safety-factor): For R-10, heater capacity = 2.75 kW For R-12, heater capacity = 2.35 kW • With the upgraded insulation, the peak load and
required equipment capacity is lower.
– This potentially means we can select lower
capacity equipment (e.g. a smaller boiler) which
could result in reduced equipment cost Simple hydronic heating system?
U Ti boiler
fuel pump piping To Comparing the two potential upgrades?
Upgrade Boiler Efficiency
• Heating energy is
reduced (lower $)
• Cost of boiler increases
(higher $) Upgrade Wall Insulation
• Heating energy is
reduced (lower $)
• Cost of wall increases
• Peak heating load is
– Smaller boiler?
– Smaller pump?
– Smaller piping?
– Lower equipment $? • It is often found that energy efficiency improvements
that save energy by a load reduction will also result in a
reduced peak load.
• Reduce heat loss/gain through roof.
• Reduce solar gains through windows (during cooling).
• Improve electric lighting.
• Avoid “excessive” ventilation. • When assessing the “cost effectiveness” of a
potential energy upgrade, it can be important to
account for the potential equipment cost savings due
• The “credit” for reducing equipment size can often
help to offset the cost of the upgrade.
• Example: Upgrading the wall insulation
• Capital cost to build wall increases by $5,000.
• Annual heating energy cost reduced by $350.
• Equipment downsizing saves $1,700 capital cost.
• Simple Payback Period = 9.4 years “Green on the Grand”
• This two-storey, 23,000 ft2 office building was built
in Kitchener in 1995.
• The exterior envelope is highly insulated and airtight.
• It has a high performance lighting system, including
occupancy sensors and day-lighting controls. Photo Credit: Enermodal Engineering Ltd. (cont’d)
• The HVAC systems includes heat recovery
ventilation, radiant heating and cooling panels, and
a ultra-high efficiency gas-fired boiler.
• The peak heating load is small enough such that the
HVAC engineer selected a residential sized boiler
(and it is able to meet the load).
• Construction cost was estimated to be only about
2% higher than typical construction.
• Annual site energy use intensity is about 120
ekWh/m2, whereas the average intensity for office
buildings in Ontario is about 400 kWh/m2. Radiant Ceiling Panels… Building Energy Performance – Spring 2012 - Topic 20 Design Charrette: “The Bauer Lofts” “ The Bauer Lofts”
• 15-storey condo
tower in Uptown
• Approx. 170
retail units on
completed ∼2009 Design Issue
• Fresh-air for the residential suites is provided using
a “pressurized corridor” system.
– The two air-handling units that provide the freshair each have a heating section, but no cooling.
Thus, at present the air can be heated before
delivery, but it cannot be cooled.
– During periods of hot weather, the corridors are
very hot and uncomfortable. Simplified Floorplan for Typical High-Rise Residential Residential
Corridor Air Duct Air Duct Elevator Stairs Residential
Suite “Pressurized Corridor Ventilation” • Air delivered to corridors through vertical ducts (air shafts)
• Air “leaks” into suites through cracks around suite doors Elec Heat Air
Duct Fresh-Air Unit Roof Corridor
/ Residential Suite exfiltration/exhaust
(to outdoors) 15th Floor Corridor
/c Residential Suite exfiltration/exhaust
(to outdoors) 14th Floor Corridor
13th Floor To other
floors Residential Suite exfiltration/exhaust
(to outdoors) Design Issue (cont’d)
• The residents recently met to discuss a quote from
an HVAC contractor to install an air-conditioning
system for the air-handlers. The...
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This note was uploaded on 10/04/2012 for the course ME 760 taught by Professor Davidmather during the Spring '12 term at Waterloo.
- Spring '12