AHP	Air heat pump
AI	Artificial intelligence
ANN	Artificial neural networking
ANOVA	Analysis of variance
AQS	Ambient air quality standards
BHE	Bore hole exchanger
BWG	Body weight gain
Cc	CO2 concentration
COP	Coefficient of performance
CO2	Carbon dioxide
Cp	Specific heat (kcal/kg °C)
Ec	Electricity consumption
ET	Expression trees
FA	Formaldehyde
FCR	Feed conversion ratio
FCU	Fan coil unit
FI	Feed intake
G	Solar radiation
GEP	Gene expression programming
GER	Geothermal energy resources
GHG	Greenhouse gas
GHP	Geothermal heat pump
GHPS	Combined geothermal heat pump and solar system
H	Humidity
HI	Heating load
H2S	Hydrogen sulphide
KOPIA	Korean Photovoltaic Industry Association
kW	Kilowatt
kWh	Kilowatt hour
M	Mass flow rate (kg/h)
MAE	Mean absolute error
NH3	Ammonia
NRE	New renewable energy
Pc	Concentration of PM2.5
PM2.5	Particulate matter
R	Correlation coefficient
RER	Renewable energy resource
RMSE	Root mean square value
SE	Solar energy
SPSS	Statistical package for social science
T	Temperature
Tm	Mean collector temperature
Ta	Ambient temperature
TVOC	Total volatile organic compounds
ΔT	Inlet˗outlet temperature difference (°C)
V	Ventilation rate
α1	Coefficient of first-order heat loss
α2	Coefficient of second-order heat loss
µ	General mean
αij	Effect of treatment
eij	Random error
Yij	Response variable
ƞcollector	Solar collector efficiency
ƞo	Optical efficiency