A Hedonic Analysis of the Impact of Tree Shade on Summertime Residential Energy Consumption

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Figure 1.
Summertime average daily electricity use and desired cooling.

Table 1a.

Sample statistics for time-invariant attributes

Attributes	Mean	Std. Dev.	Min.	Max.
Living area (ft²)	2,700.15	854.93	1,170	6,100
(m²)	(251.18)	(79.53)	(108.84)	(567.45)
Number of floors	1.52	0.51	1	3
Family size	2.5	1.13	1	7
Family size by gender
Male	1.25	0.87	0	5
Female	1.25	0.60	0	3
Family size by age group
≤12 years	0.45	0.90	0	5
13 to 24 years	0.19	0.50	0	3
25 to 60 years	1.25	0.88	0	3
>60 years	0.62	0.85	0	2
Age of the house (Yr)	14.49	12.36	1	57
Age of air conditioner (Yr)	7.52	5.85	1	32
Age of heating unit (Yr)	7.94	5.95	1	32
Age of water heater (Yr)	7.21	5.20	1	28
No. of laundry/week	5.53	3.08	1	21

Table 1b.

Sample statistics for time-variant attributes.

Attributes	Mean	Std. Dev.	Min.	Max.
kWh/day	58.50	27.59	0.02	192.97
Daytime inside temp. °F (°C)	76.35 (24.64)	2.74	70.00 (21.11)	85.00 (29.44)
Nighttime inside temp. °F (°C)	75.65 (24.25)	3.16	65.00 (18.33)	85.00 (29.44)
Outside high temp. °F (°C)	88.00 (31.11)	5.27	73.53 (23.07)	95.61 (35.34)
Outside mean temp. °F (°C)	77.84 (25.47)	5.54	62.31 (16.84)	85.03 (29.46)
Outside min. temp. °F (°C)	67.22 (19.57)	5.89	50.53 (10.29)	73.94 (23.30)
Average humidity (%)	73.72	4.06	64.02	81.20
Daytime mean temp. diff.	1.49	6.16	−16.41	15.03
Nighttime mean temp. diff.	2.19	6.35	−18.45	18.79
Percentage of house area under tree shade	17.46	19.44	0.00	88.00
Late a.m. (9–11 a.m.) percent house area under tree shade	20.93	25.30	0.00	100.00
Early p.m. (12–2 p.m.) percent house area under tree shade	10.23	14.93	0.00	90.00
Late p.m. (3–5 p.m.) percent house area under tree shade	29.86	31.19	0.00	100.00

Table 1c.

Sample statistics for categorical variables by utility or structural types.

Variables	Utility / structural type	# of sample households
Air conditioner	Central air electric	156
Air conditioner	Central air electric with window unit	4
Heating	Partially or fully electric	107
Heating	Others (natural gas, propane, etc.)	53
Cooking	Partially or fully electric	129
Cooking	Natural gas	31
Water heater	Partially or fully electric	84
Water heater	Natural gas	76
House floors	Single	77
House floors	Multiple	83
Swimming pool	Yes	12
Swimming pool	No	148
Second freezer	Yes	83
Second freezer	No	77

Table 2.

Regression results (family size and composition). Dependent variable = kWh/day.

Explanatory Variables	Model	Model 2	Model 3
Intercept	−10.450	−12.520	−9.491
Intercept	(9.622)	(9.608)	(9.747)
Family size	3.390^{^z}
Family size	(0.474)
# Females		5.250^{^z}
# Females		(0.786)
# Males		2.394^{^z}
# Males		(0.607)
12 or under			4.014^{^z}
12 or under			(0.616)
13–24			0.640
13–24			(1.081)
25–60			1.716
25–60			(1.153)
Over 60			0.847
Over 60			(1.196)
Living area	0.013^{^z}	0.013^{^z}	0.013^{^z}
Living area	(0.001)	(0.001)	(0.001)
House age	0.103y	0.108^{^y}	0.145^{^z}
House age	(0.046)	(0.046)	(0.047)
# floors	1.974^{^x}	2.231y	2.099^{^y}
# floors	(1.066)	(1.063)	(1.063)
Elec. Cooking	−1.172	−1.421	−1.025
Elec. Cooking	(1.285)	(1.283)	(1.299)
Elec. H₂O heat	4.547^{^z}	4.569^{^z}	4.007^{^z}
Elec. H₂O heat	(0.979)	(0.976)	(0.999)
Window AC	4.115	4.375^{^x}	5.437^{^y}
Window AC	(2.675)	(2.660)	(2.727)
Laundry loads/wk	1.076^{^z}	1.085^{^z}	1.142^{^z}
Laundry loads/wk	(0.169)	(0.168)	(0.169)
Second Freezer	2.475^{^z}	2.807^{^z}	2.945^{^z}
Second Freezer	(0.959)	(0.959)	(0.980)
Swimming pool	21.010^{^z}	20.84^{^z}	21.179^{^z}
Swimming pool	(1.761)	(1.757)	(1.763)
Average humidity	0.133	0.138	0.150
Average humidity	(0.127)	(0.126)	(0.126)
Daytime temp. diff. (mean)	2.233^{^z}	2.224^{^z}	2.208^{^z}
Daytime temp. diff. (mean)	(0.085)	(0.085)	(0.085)
Percent shade	−0.159^{^z}	−0.163^{^z}	−0.164^{^z}
Percent shade	(0.029)	(0.029)	(0.029)
Adj. r²:	0.5932	0.5962	0.5964
F-statistic:	170.3	160.1	140.4
N^{^w}:	1510	1510	1510

↵^zsignificant at 0.01 level
↵^ysignificant at 0.05 level
↵^xsignificant at 0.10 level
↵^wThe total number of observations for five summer months during two years was 1,510. A number of participants, out of 160, reported only one year worth of electricity data because they occupied the house only during the study year. Due to differences in monthly observations between the two years, the total number of observations is 1,510 not 1,600.

Table 3.

Regression results (shade conditions). Dependent variable = kWh/day.

Explanatory Variables	Model 1	Model 2	Model 3
Intercept	−1.543	−3.504	−10.750
	(9.556)	(9.575)	(9.592)
Family size	3.594^{^z}	3.427^{^z}	3.620^{^z}
	(0.463)	(0.467)	(0.477)
Living area	0.013^{^z}	0.013^{^z}	0.013^{^z}
	(0.001)	(0.001)	(0.001)
House age	0.057	0.101y	0.092^{^y}
	(0.042)	(0.045)	(0.047)
# floors	1.416	1.793^{^x}	1.828^{^x}
	(1.042)	(1.051)	(1.072)
Elec. Cooking	−0.912	−0.761	−0.609
	(1.271)	(1.270)	(1.291)
Elec. H₂O heat	4.443^{^z}	4.456^{^z}	4.177^{^z}
	(0.969)	(0.967)	(0.981)
Window AC	4.530^{^x}	4.428^{^x}	4.648^{^x}
	(2.642)	(2.638)	(2.670)
Laundry loads/wk	1.009^{^z}	1.009^{^z}	1.103^{^z}
	(0.168)	(0.167)	(0.168)
Second Freezer	2.519^{^z}	2.602^{^z}	2.573^{^z}
	(0.947)	(0.946)	(0.957)
Swimming pool	22.223^{^z}	21.539^{^z}	20.470^{^z}
	(1.719)	(1.739)	(1.765)
Average humidity	0.013	0.037	0.127
	(0.125)	(0.126)	(0.126)
Daytime temp. diff. (mean)	2.155^{^z}	2.192^{^z}	2.218^{^z}
	(0.083)	(0.084)	(0.085)
Percent shade		−0.088^{^y}
		(0.036)
Light shade	−0.254	0.43
	(1.431)	(1.457)
Moderate shade	−0.507	1.197
	(1.289	(1.469)
Heavy shade	−9.174^{^z}	−6.884^{^z}
	(1.356)	(1.655)
Late a.m. shade percent			0.020
			(0.028)
Early p.m. shade percent			−0.005
			(0.047)
Late p.m. shade percent			−0.117^{^z}
			(0.022)
Adj. r²:	0.6030	0.6043	0.5957
F-statistic:	153.8	145.0	149.2
N:	1510	1510	1510