**Air Enthalpy as an IAQ Indicator in Hot and Humid Environment—Experimental Evaluation**

#### **Michał Piasecki 1,\* , Krystyna Kostyrko <sup>1</sup> , Małgorzata Fedorczak-Cisak <sup>2</sup> and Katarzyna Nowak <sup>2</sup>**


Received: 17 February 2020; Accepted: 16 March 2020; Published: 20 March 2020

**Abstract:** The authors studied the impact of indoor air humidity in the range of 60% to 90% on building user perception in the temperature range of 26 to 28 ◦C. The research thesis was put forward that the impact of humidity on indoor air quality dissatisfaction of building users in a warm and humid indoor environment is greater than that indicated in thermal comfort models. The presented experiment examined the indoor air quality perception of *n* = 28 subjects in the test chamber of a nearly zero energy building under ten environmental conditions, together with a thermal comfort assessment. The authors developed an experimental relation for predicting building users' satisfaction based on the Weber–Fechner law, where the predicted percentage of dissatisfied users (*PD*) is determined by means of air enthalpy (*h*), *PD* = f(*h*). The obtained results confirmed the sated thesis. Additionally, the intersection points of the experimental function and isotherms resulting from the Fanger model are presented, where the thermal comfort assessment starts to indicate lower user dissatisfaction results than experimental values. The authors recommend the experimental equation for humid air enthalpies in the range of 50 to 90 kJ/kg. The indoor air quality assessment based on the enthalpy value is simple and can be used to determine the overall Indoor Environmental Quality index of a building (IEQindex).

**Keywords:** indoor air quality; IAQ; enthalpy; humidity; thermal comfort; TC; dissatisfaction; panel tests; nearly zero energy building; NZEB; indoor environmental quality; IEQ
