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55 wm2 k the project team wants to assess the cost

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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: losses 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 Mechanical Engineer… 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… wall U 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? wall U Ti boiler losses baseboard heater 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 (higher $) • Peak heating load is reduced – 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. Some examples: • 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 to downsizing. • 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” Condominiums • 15-storey condo tower in Uptown Waterloo • Approx. 170 residential suites; retail units on ground floor • Construction 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 Suite Residential Suite Residential Suite Trash Rm Stairs Corridor Air Duct Air Duct Elevator Stairs Residential Suite Residential Suite Residential Suite Residential Suite 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 Intake Fresh-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 /c 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.

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