1. Lecture Objectives Finish the cooling load example
Learn about Heating Systems

2. HW2 due date Moved to March 5th
On Friday we will have TA office hours to help with specific questions for this HW

3. Example problem
Calculate the cooling load for the building in Pittsburgh PA with the geometry shown on figure. On east north and west sides are buildings which create shade on the whole wall.
Windows: Champion Window CDP number CHW-A-8
Walls: 4” face brick + 2” insulation + 4” concrete block, Uvalue = 0.1, Dark color
Roof: 2” internal insulation + 4” concrete , Uvalue = , Dark color
Below the building is basement wit temperature of 75 F.
Internal design parameters:
air temperature 75 F
Relative humidity 50%
Find the amount of fresh air
that needs to be supplied by
ventilation system.

4. Example problem (continuing)
Internal loads:
10 occupants, who are there from 8:00 A.M. to 5:00 P.M. doing moderately active office work
1 W/ft2 heat gain from computers and other office equipment from 8:00 A.M. to 5:00 P.M.
0.2 W/ft2 heat gain from computers and other office equipment from 5:00 P.M. to 8:00 A.M.
0.5 W/ft2 heat gain from suspended fluorescent lights from 8:00 A.M. to 5:00 P.M.
0.1 W/ft2 heat gain from suspended fluorescent lights from 5:00 P.M. to 8:00 A.M.
Infiltration:
0.5 ACH per hour

5. Example solution SOLUTION steps (see handouts):
1. Calculate cooling load from conduction through opaque surfaces using TETD.
2. Calculate conduction and solar transmission through windows.
3. Add sensible internal gains and infiltration.
4. The result is your raw sensible cooling load.
5. Calculate latent internal gains.
6. Calculate latent gains due to infiltration.
7. The sum of 5 and 6 is your raw latent cooling load.

6. Example solution SOLUTION: For which hour to do the calculation ?
With computer calculation for all and select the largest.

7. Example solution
For which hour to do the calculation when you do manual calculation?
Identify the major single contributor to the cooling load and do the calculation for the hour when the maximum cooling load for this contributor appear.
For example problem major heat gains are
through the roof or solar through windows!
Roof: maximum TETD=61F at 6 pm (Table 2.12)
South windows: max. SHGF=109 Btu/hft2 at 12 am (July 21st Table 2.15 A)
If you are not sure, do the calculation for both hours:
at 6 pm
Roof gains = A x U x TETD = 900 ft2 x 0.12 Btu/hFft2 x 61 F = 6.6 kBtu/h
Window solar gains = A x SC x SHGF =80 ft2 x 0.71 x 10 Btu/hft2 = 0.6 kBtu/h total = 7.2 kBtu/h
at 12 am
Roof gains = A x U x TETD = 900 ft2 x 0.12 Btu/hFft2 x 30 F = 3.2 kBtu/h
Window solar gains = A x SC x SHGF =80 ft2 x 0.71 x 109 Btu/hft2 = 6.2 kBtu/h total= 9.4 kBtu/h
For the example critical hour is July 12 AM.

8. Solution
On the board

9. Heating systems

10. Choosing a Heating System
What is it going to burn?
What is it going to heat?
How much is it going to heat it?
What type of equipment?
Where are you going to put it?
What else do you need to make it work?

12. Choosing a Fuel Type Availability Storage Cost Code restrictions
Emergencies, back-up power, peak demand
Storage
Space requirements, aesthetic impacts, safety
Cost
Capital, operating, maintenance
Code restrictions
Safety, emissions

13. Selecting a Heat Transfer Medium
Air
Not very effective (will see later)
Steam
Necessary for steam loads, little/no pumping
But: lower heat transfer, condensate return, bigger pipes
Water
Better heat transfer, smaller pipes, simpler
But: requires pumps, lower velocities, can require complex systems

14. Choosing Water Temperature
Low temperature water (180 °F – 240 °F)
single buildings, simple
Medium and high temperature (over 350 °F)
Campuses where steam isn’t viable/needed
Requires high temperature and pressure equipment
Nitrogen system to prevent steam formation

15. Choosing Steam Pressure
Low pressure (<15 psig)
No pumping for steam
Requires pumping/gravity for condensate
Medium and high-pressure systems
Often used for steam loads

16. Steam Systems Steam needs bigger pipes for same heat transfer
Water is more dense and has better heat transfer properties

17. What About Air? Really bad heat transfer medium But !
Very low density and specific heat
Requires electricity for fans to move air
Excessive space requirements for ducts
But !
Can be combined with cooling
Lowest maintenance
Very simple equipment
Still need a heat exchanger

19. Furnace Load demand, load profile Efficiency Combustion air supply
Amount and type of heat
Response time
Efficiency
80 – 85 % is typical
Electricity is ~100 %
Combustion air supply
Flue gas discharge (stack height)

20. Choosing a Boiler Fuel source Transfer medium
Operating temperatures/pressures
Equipment
Type
Space requirements
Auxiliary systems

21. Water Boilers Types Water Tube Boiler Fire Tube Boiler
Water in tubes, hot combustion gasses in shell
Quickly respond to changes in loads
Fire Tube Boiler
Hot combustion gasses in tubes, water in shell
Slower to respond to changes in loads

23. Electric Types Resistance Electrode
Resistor gets hot
Typically slow response time (demand issues)
Electrode
Use water as heat conducting medium
Bigger systems
Cheap to buy, very expensive to run
Clean, no local emissions

24. Auxiliary Burner type (atmospheric or power vented) Feedwater systems
Returns steam condensate (including accumulator)
Adds water to account for blowdown and leaks
Preheats the water
Removes dissolved gasses
Blowdown system
Periodically drain and cool water

25. Auxiliary Water treatment Treatment options
Dissolved minerals and gasses cause:
Reduced heat transfer
Reduced flow (increased pressure drop)
Corrosion
Treatment options
Chemical (add bases, add ions, add inhibitor)
Temperature (heat to remove oxygen)

26. Location Depends on type Aesthetics Stack height
Integration with cooling systems

27. Reading Assignment
Tao and Janis Chapter 5