Calculations for the size of the HVAC system in Macalister hall will be completed through two methods. The first method will be based on cfm and tonnage estimates set forth in ASHRAE. The second method, which is more detailed, involves the use of the Carrier E-20 simulation program to calculate the loads.
ASHRAE Estimation Standards:
ASHRAE sets forth standards for the estimation of the cfm and tonnage in a building. Using a 20 cfm/person standard and a reheat system, ASHRAE sets forth the numbers as follows:
For our estimations, we will use the midpoints of these values to result in an answer that is neither too liberal nor too conservative.
ASHRAE Estimation Method for Macalister Hall:
The total square footage of conditioned space in Macalister Hall is as follows:
Based on the square footages calculated above and the ASHRAE standards outlined previously, the building loads are calculated in the following table:
Carrier E-20 Program
The Carrier E-20 program is much more accurate than the previously mentioned estimation. Through this software program, the building loads are calculated while taking into account construction materials, directional facing, infiltration, schedules of occupancy, equipment loads, people loads, and other setpoints within the HVAC system. The data input to the program is outlined below.
Philadelphia Region Temperatures
Philadelphia Elevation Above Sea Level: 26 ft
Philadelphia Latitude Location: 40°
Construction Materials Information:
The following sections show the two main forms of construction for Macalister Hall. The tower is composed of a 6" precast concrete panel on the outside, a large air space, and a interior course of 4" concrete block. The first floor has a 4" brick exterior, a 1" air gap, and 8" concrete block wall.
1st Floor Wall Section Tower Wall Section
From the above wall sections, I calculated the overall U value of the walls (Btu/hr/ft2/°F) based on the materials used and the standards set forth in ASHRAE. The tabulated values are as follows:
1st Floor Construction:
Typical Window Construction:
Assumed an aluminum double paned window with a thermal break and light shades on the inside. These assumptions lead to the following values:
Typical Roof Construction:
Assumed a built-up roof on a 22-gage steel deck with R-7 board insulation. These assumptions lead to the following value:
Typical Lighting Loads: 1.5 Watts/ft2
Typical People Loads: 1 person/ 150 ft2 doing office work:
Typical Infiltration Losses: 2 air changes/hour
Typical Equipment Loads: .5 Watts/ft2
Setpoints and Safety Factors:
Equations Used by E-20 to Calculate Loads:1. Heating Load: Q = U x A x T
The area of wall was calculated using a floor to floor height of 12'-0" in the tower and 15'-0" on the first floor.
2. Cooling Load: Q = U x A x CLTDc
The CLTDc is a modified value for the temperature difference that takes into account heat storage and time lag effects.
3. Solar Radiation through glass: Q = SHGF x A x SC x CLF
The SHGF is based on orientation and time of year and the SC is based on the type of drapery placed on the window.
4. Lighting Load: Q = 3.4 x W x BF x CLF
The BF accounts for heat losses in the ballasts of fluorescent lights and the CLF accounts for heat storage in the lighting fixtures.
5. People Loads: Qs = qs x n x CLF, Ql = ql x n
Carrier E-20 Results:
From the above setpoints and equations, the information was entered into the Carrier E-20 program and the following results were given: