Lecture 7Chapter 5 (cont’d)

• Is Color of Building Materials Important?

• DD

• Cooling

• Air Conditioning & Heat Pumps

• COP

How does color affect my wallet?

• Proper energy environment– Dark colors absorb heat energy– Light colors reflect heat energy

• Building Location– South and Southwest

• Roofs are light colored• Siding is white adobe or vinyl

– North• Roofs are very dark• Siding tends to be darker with dark trim

– Midwest• Both types are seen

What Good are Degree Days?

• Heating professionals use them to calculate heat load requirements to keep your home warm during heating season.

• Infiltration losses in Btu/hr:

Qinfil/t = 0.018 x V x K x ∆T

V: house volume; K: air changes/hr (0.5-1.5)

∆T = Tin – Tout, where Tout is average coldest

• Total Q = Qinfil + Qcond

• Furnace required = Total Q/efficiency of furnace

• Annual cost is total of infiltration plus heat loss

• QtotalDD = R x A) x (24hr/day) x (annual DD)

• QinfilDD = 0.018 x V x K x 24hr/day x DD

• Annual cost =

(QtotalDD + QinfilDD) x (kWh/3413Btu) x (cost/kWh)

Passive Heating & Cooling

• Site Selection: location, orientation, vegetation

• Architectural features

Fig. 5-9, p. 144

In most of the US, average temperature of the earth below the frost line is 55 to 57oF (13 to 14oC). Frost lines can range from 20 to more than 40 in.

Fig. 5-12, p. 148

Fig. 5-13, p. 149

Phase Changes Make Air Conditioners Work

• CFC-12 (R-12) replaced with HFC-134a Used in car air conditioners

• CFC-22 (R-22) replaced with R-410a (blend of R-22 & HFC’s) Low temperature applications: Freezers, Refrigerators, Commercial

applications, Air Conditioners

• New Families of Refrigerants fluoroiodocarbons (FICs), HC Refrigerants (see also: ODP, GWP)

• No new equipment to be built after 2010 that uses CFCs

• No CFCs made after 2020

p. 150

Fig. 5-14a, p. 150

Fig. 5-14b, p. 150

Fig. 5-15, p. 152

Fig. 5-16, p. 153

Table 5-4, p. 154

Example Problem

Assumptions– House built in 1950’s in Southern Illinois

• Has Crawl Space• Walls are insulated to R11• Ceiling is insulated to R11• Floor insulated to R11• Air changes per hour = 3• 900 sq.ft. home( 30’ x 30’ )

– DD = 4500– Ambient temperature = 25°F

What is the yearly total heat transfer from the home and what is the energy requirement to maintain home at 65°

with a furnace efficiency of 80%?

• Qc = (A/R) x (24hrs/day) x 4500 DD R = 11 for all surfaces

Aw = 30’x8’x4 walls

Acf = 900 sq ft

• Qc = ((960+900*2)/11)*24*4500 = 27.1x106 Btu/yr

• Qinfil = 0.018 x V x K x 24xDD• Qinfil = 0.018*7200*3*24*4500

= 42x106 Btu/yr

• Qtotal = Qc + Qinfil

= 27.1x106 Btu + 42x106 Btu

= 69.1x106 Btu/yr

• Qfurnace = 69.1x106/0.8 = 86.4 MBtu/yr

• Cost of electric heating

= $0.11/kWh x (1kWh/3413 Btu) x Qfurnace = $2784.65