H, h
H2
he
hp
hph
H2S
I
i
Io
J
K
KA
kcal
K2O
kWh
L
I
Ld
lrn
mbar
MgO
mWG
N
N
N
n.c.v.
NP
P
P
p
p
pa
PE
pE
PN
P2O5
PVC
PW
pw
Q
QW
R, r
Re
ROI
RT
Sd
T, t
tc, max
T,D.C.
tz, max
height
hydrogen
height of earth column
horsepower
horsepower-hour
hydrogen sulfide
luminous intensity
discounting factors/calculatory (assumed) interest rate
initial investment
joule
potassium
average capital invested (per time interval)
kilocalorie
potassium oxide
kilowatt hour
latent heat of evaporation
length of pipe
digester loading
lumen
millibar
magnesium oxide (magnesia)
meter water gage
nitrogen
burner efficiency
Newton
net calorific value (in diagrams: n.c.v. = Hu)
net profit
pressure/gas pressure
phosphorus
market rate of interest
biogas/energy production
Pascal
polyethylene
active earth pressure
normal pressure
phosphorus pentoxide
polyvinyl chloride
partial pressure of water vapor
hydrostatic pressure
gas flow
quantity of heated water
radius
luminous efficiency
return on investment (profitability)
retention time
daily substrate input
temperature
maximum consumption time
top dead center
maximum period of zero consumption
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