  We develop a data-driven, {\em Partial Differential Equation-Ordinary
Differential Equation} (PDE-ODE) model that describes the response of the {\em
Carbon Dioxide} (\cotwon) dynamics inside a conference room, due to the
presence of humans, or of a user-controlled exogenous source of \cotwon. We
conduct two controlled experiments in order to develop and tune a model whose
output matches the measured output concentration of \cotwo inside the room,
when known inputs are applied to the model. In the first experiment, a
controlled amount of \cotwo gas is released inside the room from a regulated
supply, and in the second, a known number of humans produce a certain amount of
\cotwo inside the room. For the estimation of the exogenous inputs, we design
an observer, based on our model, using measurements of \cotwo concentrations at
two locations inside the room. Parameter identifiers are also designed, based
on our model, for the online estimation of the parameters of the model. We
perform several simulation studies for the illustration of our designs.
