Required and current thermal conditions for occupants in Iranian hospitals

HVAC & R Research, March, 2008 by Jamal Khodakarami, Ian Knight

AIMS OF THE STUDY

The aims of this study are as follows:

1. Determine the conditions required for thermal comfort by patients and staff of Iranian hospitals.

2. Investigate the current thermal comfort conditions being achieved in Iranian hospitals.

3. Suggest potential solutions to improving thermal comfort achievement in the investigated buildings.

BACKGROUND

Thermal Comfort in Hospitals

A large volume of thermal comfort research over the last century has been distilled into international standards in terms of designing and maintaining comfortable thermal environments (de Dear 2004). During this time, the two main approaches to thermal comfort research have been (1) the laboratory-based method, e.g., Fanger's PMV-PPD model (Fanger 1970), which led to ISO 7730, Moderate Thermal Environments--Determination of PMV and PPD Indices and Specification of the Conditions of Thermal Comfort (ISO 2005), and (2) the field-based method, e.g., the Adaptive Comfort Standard (ACS). Both of these methods are represented in the latest edition of ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy (ASHRAE 2004). Thermal comfort can be expressed as "that condition of mind which expresses satisfaction with the thermal environment" (ISO 2005). Air temperature, radiant temperature, humidity, and air movement, as the environmental variables, combine with the metabolic heat generated by human activity and clothing worn by a person to provide the six fundamental factors that define human thermal environments (Parsons 2003).

A study on patient thermal requirements in hospital environments was undertaken in Taiwan based on both subjective and objective methods. The study concluded that physical strength has a highly significant effect on thermal comfort sensation whereas gender, age, and acclimatization do not. The study also concluded that patients expect a warmer indoor environment than neutrality (Hwang et al. 2007).

The thermal comfort of patients and hospital staff is affected by the thermal conditions provided, including air temperature and relative humidity (RH), in hospital wards (Skoog et al. 2005). Due to different levels of clothing and activity between patients and hospital staff, these groups require different conditions to achieve thermal comfort. The thermal conditions required to produce thermal comfort are further complicated by the fact that patients with different complaints may be located in the same wards. So to achieve the best balance of comfort, it is necessary to first establish the conditions needed to achieve thermal comfort for patients and staff in hospitals.

Reviews of the adaptive thermal comfort models show that these indicate wider bands of temperature where the occupants may still achieve thermal comfort. Comparisons between the static model (PMV) and the adaptive models for thermal comfort show that the PMV model is more accurate in buildings with HVAC systems and the adaptive models are more appropriate to buildings with natural ventilation (de Dear and Brager 1998). Therefore, as the Iranian hospitals evaluated in this study have HVAC systems, the PMV method was selected for this study to predict the required thermal conditions for the occupants of these buildings.

The Iranian regulations for health-care buildings recommend the use of air-conditioning systems for health-care buildings, considering the need to control hygiene problems, the types of activity, and the occupants of these buildings (MPO 2004).

To support the findings from this study, the authors believe that it is important to undertake subjective studies to present the actual thermal sensations of occupants in the buildings. However, due to subject protocols and also some other limitations it was difficult to undertake a formal subjective study, particularly in the form of questionnaires, in Iranian hospitals. Therefore, informal interviews with patients and hospital staff are used in this research; indoor thermal comfort dissatisfaction was a common complaint in the interviews.

The thermal comfort conditions were ascertained through a combination of monitoring those parameters that affect occupant thermal comfort along with occupant and site observations. The findings from the monitoring are compared with the Iranian MPO standard and international thermal comfort standards from ASHRAE, ISO, and CIBSE.

Of the standards used, CIBSE (CIBSE 1999) and Iranian standards (MPO 2004) indicate the indoor air temperature and RH ranges for thermal comfort achievement. ISO 7730 (ISO 2005) and the latest revision of ASHRAE Standard 55 (ASHRAE 2004) indicate a range for predicted mean vote (PMV) or predicted percentage dissatisfied (PPD) to achieve thermal comfort based on the six factors that define PMV or PPD: air temperature, RH, radiant temperature, clothing levels, activity levels, and air velocity (Olesen and Parsons 2002). Table 1 presents the relevant thermal comfort ranges from the standards.

Table 1. Recommended Conditions to Achieve Thermal Comfort

     Standard       Recommended Thermal Condition to Achieve Thermal
                                        Comfort

    ASHRAE 55       -0.5 < PMV <  0.5; PPD < 10%; 0 < humidity ratio
                                        < 0.012

     ISO 7730         -0.5 < PMV <  0.5; PPD < 10%; 30% < RH < 60%

      CIBSE         22[degrees]C < Temperature < 24[degrees]C; 30% <
                                        RH < 60%

Iranian Regulation      20[degrees]C < Temperature < 23[degrees]C
      (MPO)              (winter), 24[degrees]C < Temperature <
                         28[degrees]C  30% < RH < 60% (summer);