Analysis of HVAC indoor terminal units by using T-Q diagram : an experimental study

The T-Q diagram is a widely used tool in the industry to optimize the design and the number of heat exchangers in a process. The principle consists in minimizing the quantity ∫TdQ in WK called entransy dissipation. We performed an experimental study in climatic chamber in order to apply the T-Q diagram method for the choice of the best indoor terminal device in an office submitted to a summer climate in Brussels and for the choice of the operating parameters water flow rate and water temperature. We tested four terminal units coupled to a cooling water tank by using a reversible air-water chiller: a mixing ventilation, a displacement ventilation, the mixing ventilation combined with a low inertia hydronic radiant floor, the displacement ventilation combined with the low inertia hydronic radiant floor. The tests were performed under stationary conditions. We plot the T-Q diagram and we assessed the entransy dissipations for each system and various operating parameters. We measured thermal comfort within the climatic chamber. Tests showed that air systems were less efficient than ventilation combined
with radiant floor and that the combination of displacement ventilation with radiant floor was the best system. The study also showed that entransy dissipation values represented the real quality of the indoor terminal units.