# The Interplay between Air Quality and Energy Efficiency in Museums, a Review
## 3 Results and Discussion  
### Indoor Air Quality and Energy Consumption Fundamentals  
IAQ is affected by the concentrations of air pollutants, gases, or particles in the atmosphere. Indoor air pollutants can be transported from outside or emitted from inside. The indoor air pollutant concentrations and their diurnal variation will be shaped by building characteristics such as air exchange rate, material of the indoor surfaces, and occupant activity. Depending on the indoor activities, atmospheric pollutants emitted indoors may be the most serious threat to poor indoor air quality. To demonstrate this, a simple indoor model, shown in Figure 1, is discussed below. In each room or in an entire building, where air can be assumed to be well mixed, the rate of change of an air pollutant concentration can be described by a mass balance equation, as follows [37; 38]:  
\[V\frac{dC_{in}}{dt}=PfC_{out}-fC_{in}+S-R \tag{1}\]  
where \(C_{in}\) and \(C_{out}\) are the respective indoor and outdoor atmospheric pollutant concentrations (\(\mu\)g m\({}^{-3}\)); f is the air flow rate (m\({}^{3}\) h\({}^{-1}\)); the room air exchange rate (AER) is equal to \(f/V\) (h\({}^{-1}\)); and \(S\) represents the emission rate of the air pollutant from the indoor sources (\(\mu\)g h\({}^{-1}\)). The air pollutant loss rate \(R\) can be considered to be equal to \(u_{d}AC_{in}\), where \(k=u_{d}\frac{A}{V}\) (h\({}^{-1}\)) is the average deposition rate of each pollutant on indoor surfaces. \(V\) is the volume of the room (m\({}^{3}\)), A is the total interior surface area (m\({}^{2}\)), and \(u_{d}\) is the average deposition velocity of each air pollutant (m h\({}^{-1}\)). The parameter \(P\) only refers to PM and is defined as the particle penetration coefficient (dimensionless) [39]. In the case of gaseous pollutants, \(P=1\). Certainly, the simple Equation (1) does not account for all of the variables that influence indoor air pollutant concentrations. Indoor chemical reactions, as well as coagulation or phase change processes in the case of PM, interfere with the terms \(S\) and \(R\); deposition velocities are not stable and can be different for the diverse orientation of the surfaces; other phenomena also influence the indoor air pollutant concentrations [38; 40; 41; 42]. Based on the simple model above, we can refute the widely held belief that changing the AER of a room would always improve its air quality. Indoor air pollution problems are not always solved by simply changing the AER. The solution is dependent on a combination of outdoor and indoor air pollutant concentrations, indoor air pollutant emission and loss rates, etc., and each combination is unique and may not be applicable for all pollutants under consideration [43; 44]. Many studies use CO\({}_{2}\) concentrations as an indicator of IAQ. Indoor CO\({}_{2}\) concentrations are affected by the number of occupants, their metabolic rate, and in buildings without combustion sources, such as museums, they are only indicative of whether the AER is adequate for bio-effluent dilution [45]. Numerous other indoor air pollutants contribute to poor indoor air quality [46]. VOCs, for example, can come from both outdoor and indoor sources, such as human breath, personal care products, and cleaning products [47; 48; 49; 50]. The materials that are used in the construction of the display cases can be also a source of dangerous VOCs, such as formic and acetic acid [51]. Particulate matter of various chemical compositions and sizes causes concern for human health, but it also endangers works of art [52; 53]. As a result, there is no universal solution for every difficult indoor air pollution situation. An extensive IAQ monitoring program is required to propose IAQ control measures in each case. [PERSON] and [PERSON] [54] explain that in a building with a heating, ventilation, and air conditioning (HVAC) system, the main link between IAQ and EEF is the parameter f in Equation (1), which is the air flow rate that infiltrates or exfiltrates (or exhausts) from the room per unit of time.