## 2 Literature Review
The research benefits maintenance decisions in healthcare facilities, proposes innovative design methods and fault detection approaches, and highlights the importance of reliability modelling for improved system performance and cost savings, which are summarized in Table 1.  
The publication data was retrieved from the Scopus database for bibliometric analysis using the keywords/terminologies \"reliability AND analysis AND fault AND HVAC AND system AND fault\". Figure 1 depicts a keyword network related to research on HVAC system reliability and fault analysis. More than 100 papers were published in this domain in last 15 years. The size and color of the nodes represent the frequency of occurrence of the keywords in the research papers. The lines connecting the nodes indicate the co-occurrence of the keywords, with thicker lines representing stronger relationships. This visualization helps identify key research areas and potential synergies within the field. \begin{table}
\begin{tabular}{|p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline
**Ref. ** & **Distribution** & **Reliability** & **Mainability** & **Availability** & **Method Used** & **Application Domain** & & & & & & & & \\ \hline
[1] & \multirow{2}{*}{Lognormal} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & & & & & & & & & & \\  & & & & & & & &  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Ref. ** & **Distribution** & **Reliability** & **Maintainability** & **Availability** & **Method Used** & **Application Domain** & **Finding/Observations** \\ \hline
[27] & Ben-fit distribution & & & Monte Carlo simulation & Commercial buildings & & The Monte Carlo simulation was used to improve the accuracy of the load predictions. The parameters considered for model development were the temperature, native humidity, solar radiation, occupancy, and light power. & \\  & & & & & A multistudy assessment algorithm for commercial AC system & system loads was developed for flexible loading conditions. & \\
[28] & - & Optimization & Commercial AC system & Facility design should appropriately consider heat generation needs, building structure, and maintenance systems. & \\
[25] & & & FDD algorithm & review & The fault detection and diagnosis (FDD) algorithms that cover all common HVAC links for traditional and non-traditional HVAC systems were reviewed. & \\
[40] & & & & Uncertainty and sensitivity analyses & Commercial building & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & & \\ \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Ref.** & **Distribution** & **Reliability** & **Maintainability** & **Availability** & **Method Used** & **Application Domain** & **Finding/Observations** \\ \hline
[34] & Normal distribution & **-** & & & Stress-strength model & Aero-engine & A dynamic stress-strength-based reliability model was developed and analyzed for an aero-engine used in the development of the new energy-based model. & & \\  & Normal distribution & **-** & & & Stress-strength model & Aero-engine & The accuracy of the proposed model was higher than that of traditional models, especially complex and adaptable flight curves with an existing impact load. & \\  & & & & & & The Layer Recurrent Network (IBN) approach was used for modeling and an PDG algorithm of the HVAC system was used, which does not require a plant fault history. & \\  & & & & & & The constructed Health Index (H) matrix directly reflects the health status of the aircraft all-conditioning system and has high reliability. & \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._Even with significant advancements, there is a need to develop a robust, accurate, and comprehensive method for HVAC reliability analysis that takes environmental effects and actual operating conditions into account.