'CFD simulation to evaluate thermal comfort in a restaurant' simulation project by vaibhav_s


#1

I created a new simulation project called 'CFD simulation to evaluate thermal comfort in a restaurant':

In this project we evaluate the thermal comfort parameters inside a restaurant


More of my public projects can be found here.


#2

Thermal Comfort in a Restaurant with CFD

The Engineering Problem

Human thermal comfort is defined as the state of mind that expresses satisfaction with the surrounding environment. It is achieved by maintaining a thermal equilibrium between the environment and human body. The optimization of thermal comfort in buildings has become one of the vital aspects during the conception phase of HVAC systems.

A human body continuously generates heat at a rate varying from about 100 W (e.g. for a sedentary person) to as high as 2000 W (e.g. for a person doing strenuous exercise). Continuous heat generation is essential, as the temperature of the human body has to be maintained within a narrow range of temperature, irrespective of the external surroundings.
 
Studies show that at neutral condition, the human skin and core temperatures should be 33.7 and 36.8 °C respectively.

 
Factors affecting thermal comfort:-

1. Physiological factors such as age, activity, sex and health.
These factors influence the metabolic rate. It is observed that of these factors, the most important is activity. Other factors are found to have negligible effect on thermal comfort.
 
2. Insulating factor due to clothing.
The type of clothing has strong influence on the rate of heat transfer from the human body. The unit for measuring the resistance offered by clothes is called as “clo”. 1 clo is equal to a resistance of about 0.155 m2.K/W. Typical clo values for different types of clothing have been estimated and are available in the form of tables. For example, a typical business suit has a clo value of 1.0, while a pair of shorts has a clo value of about 0.05.
 
3. Environmental factors
Important factors are the dry bulb temperature, relative humidity, air motion and surrounding surface temperature. Of these the dry bulb temperature affects heat transfer by convection and evaporation, the relative humidity affects heat loss by evaporation, air velocity influences both convective and evaporative heat transfer and the surrounding surface temperature affects the radiative heat transfer.

 
Apart from the above, other factors such as drafts, asymmetrical cooling or heating, cold or hot floors etc. also affect the thermal comfort. The objective of a comfort air conditioning system is to control the environmental factors so that comfort conditions prevail in the occupied space. It has no control on the physiological and insulating factors. However, wearing suitable clothing may help in reducing the cost of the air conditioning system.

 
ASHRAE STANDARD 55 - 2004 presents a method for evaluating the thermal sensation and the degree of discomfort of people exposed to moderate thermal environments. It also specifies acceptable environmental conditions for comfort. It can be applied to indoor environments where the aim is to attain thermal comfort.
 
Since so many factors are involved, many combinations of the above conditions provide comfort. Therefore, to evaluate the effectiveness of the conditioned space, several comfort indices exist. These indices can be divided into direct and derived indices. The direct indices are the dry bulb temperature, humidity ratio, air velocity and the mean radiant temperature.
 
The derived indices combine two or more direct indices into a single factor. Important derived indices are the Predicted Mean Vote (PMV), Percent of People Dissatisfied (PPD), effective temperature, operative temperature, heat stress index, etc.
 
The PMV, Predicted Mean Vote, that predicts the mean response of a large number of occupants is defined based on the thermal sensation scale and so is estimated from six variables: clothing insulation, activity level, air temperature, air velocity, air humidity, and mean radiant temperature. Generally, air temperature and the metabolism of the human body significantly affect the PMV value.
 
The thermal sensation scale:-
thermalSensation
 
PPD (predicted percentage of dissatisfied) index is related to the PMV as follows:-
pmvPPD
 
PPD10

 
Even when the PMV 0, there will still be some individuals who are dissatisfied with the temperature level, regardless of the fact if they are all dressed similarly and have the same level of activity as comfort evaluation differs a little from person to person.
 
Metabolic Rates for Typical Tasks:-

activity

Project Overview

The aim of the project is to evaluate thermal comfort inside a restaurant with CFD simulation. Steady State Convective heat transfer solver with Boussinesq approximation is used along with k - omega SST turbulence model.

 
Assumptions:-
Relative Humidity = 50%
Mean Radiant Temperature = Air Temperature
Clothing Coefficient = 1.0

 
CAD

 
Mesh

 

Simulation Results

 

Velocity at 1.1m (head height for seated person)

 
Temperature at 1.1m

 
EDT at 1.1m

 
PMV at 1.1m

 
PPD at 1.1m