CFD Basement ventilation queries

1. Do we need to do CFD analysis to decide the location (Orientation) and the number of fans in a basement or we can decide on the basis of other factors solely? What are the calculations for the same? What is the threshold velocity of air to be considered stagnant? 2. How much area does a louver cover in general? The louver generally covers 30-60 percent of the total available area. So we need to ask the client before hand as to what is the particular configuration. 3. What are the guidelines for the ventilation projects? 4. Formulas and other basic calculations See Section B Below 5. How can we optimize on the number and location of fans, any other thumb rule other than area consideration. ? What are the parameters which decide the placement of fans and how do we check on the location of fans? Everything about the location of fans, how do we give the deliverable in terms of its place and how much buffer do we have in terms of angle or orientation from proposed ones in the drawing? 6. How do you calculate the effective area for the CFD domain in AutoCAD? It is the units conversion which confuses me. 7. Which standard says that the fresh air is supposed to be considered at 2.5 m/s 8. Exact details of the fresh air source, shape, size and area for natural and velocity in addition for mechanical air intake sources to get CFM of fresh air intake. 9. We need layout, sectional and coordinated drawings for the project 10. Make a document which mentions all the requirements needed from the client for initial response. 11. Give a brief of the working procedure for Phoenics. (Earth, satellite, Photon etc.) 12. NBC Section 1 part 8 13. ISO 7730 See section A below 14. Units of smoke (SMOK) 15. In Phoenics, how do we change the number of cells in the domain? 16. SLEN Visibility --> Min 8 meter and Ideally 30 meters. Confirm on it 17. Read CHAM technical report TR313 18. What is meant by P1,U1,V1 and W1 shown in Earth P1 Pressure U1, V1, W1 Fluid particle velocities in x, y and z direction

19. SWIRL Number It is required when working with FANS in Phoenics, The Swirl Number is the ratio between the tangential velocity and the axial velocity

Section A
ISO 7730 Moderate thermal environments Determination of the PMV and PPD indices and specification of the conditions for thermal comfort This standard describes the PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) indices and specifies acceptable conditions for thermal comfort. The PMV predicts the mean value of the votes of a large group of people on the ISO thermal sensation scale (+3 = hot; +2 = warm; +1 = slightly warm; 0 = neutral; -1 = slightly cool; -2 = cool; -3 = cold). The PPD predicts the percentage of a large group of people likely to feel too warm or too cool. The indices are exactly as described by Fanger (1970). A draft rating index is provided in the standard as an equation involving air temperature, air velocity and turbulence intensity. It is applicable to mainly sedentary people wearing light clothing with a whole-body thermal sensation close to neutral. Recommended thermal comfort requirements are provided in Annex D of the standard (informative not a formal part of the standard). This includes optimum operative temperature; vertical air temperature gradient; mean air velocity; floor temperature; and relative humidity. ISO 7730: Validity The PMV/PPD indices have been extensively investigated throughout the world and mostly in terms of validity. Does the PMV accurately predict the Actual Mean Vote (AMV) of people? Empirical research has led to mixed results and discussion of interpretation. Laboratory studies have often supported the validity of ISO 7730 whereas field studies have not. However, the interpretation of results often involves discussion of the sensitivity of the method to estimates of variables such as metabolic heat and clothing insulation which are difficult to estimate and, in practical situations (along with the other parameters), often vary. Other issues are concerned with the sensitivity of the method. How well can the method distinguish between comfort conditions? How well does it need to? If we achieve statistical significance between AMV and PMV of 0.1 of a scale value, does this have practical significance? Practical significance will depend upon context, but what difference between AMV and PMV would encourage standards makers to revise the standard on the grounds of validity? ISO 7730 has been criticized because of its lack of theoretical validity. The PMV/PPD indices were established in 1970. Since then there have been improvements to the human heat balance equation. There are also dynamic models of human thermoregulation that offer more accurate representations of physiological measures such as mean skin temperature and sweat rate. The prediction of sensation away from neutrality (towards warm or cool) is based upon the principle of thermal load. This has been criticised (Humphreys and Nicol, 1996). A more valid approach may be to predict deviation from neutrality using predictions of body state, such as skin temperature, sweat rate, or skin wettedness (Gagge et al., 1971). Related

to the validity of ISO 7730 is the validity of ISO 8996 metabolic rate and ISO 9920 clothing. The estimation of metabolic heat production and clothing insulation (two parameters to which the PMV is particularly sensitive) and other properties are difficult, especially when considering practical, dynamic contexts. This raises the question as to whether a valid rational thermal index or model is possible.

Why continue to improve the heat balance equation or develop thermal models when the complexity of reality will undermine any improvement? The adaptive model of thermal comfort has questioned validity and this is also related to scope. The question of validity is related to how well the methods in the standard (PMV, etc.) relate to the actual thermal comfort responses of people. If people change their thermal comfort response with prevailing outside climatic conditions (for exactly the same clothing, activity and indoor climate) the standard will not respond to this and it will have reduced validity. If different populations and cultures differ in thermal comfort responses (to identical clothing, activity and indoor climate) then the standard will have reduced validity for some populations. If the standard does not include those populations in its scope (e.g. people from Africa, Asia, etc.) then the standard may be valid but should it be accepted as a universal international standard? ISO 7730: Reliability Defining the PMV/PPD in an international standard provides the major advantage of ensuring that when it is calculated anywhere in the world the same result will be obtained. However, if two assessments were made of identical conditions, by different users, or the same user on a different occasion, identical outcomes may not be achieved. Methods for estimating metabolic rate (ISO 8996), clothing insulation (ISO 9920), and environmental parameters (ISO 7726) will influence reliability as will ambiguities in the standard about where and when to assess the environment ISO 7730: Usability It is not clear who the users of ISO 7730 are intended to be and this clouds a discussion of usability. However it is probably reasonable to assume that those involved in environmental design and assessment, building services, engineering and ergonomics would be users. The PMV/PPD indices provide clear predictions of likely discomfort and dissatisfaction. It could be argued however that exactly how to measure or estimate input parameters for the model are technical and not exact. Examples, in an annex to the standard, of how it can be used would aid usability. Usability testing where groups of users were observed using the standard and feedback provided would also improve the usability of the standard. ISO 7730: Scope The scope of a standard is concerned with to what it does and does not apply. ISO 7730 can be considered in terms of to whom it applies and over what range of environmental conditions. The PMV/PPD index was developed using North American and European people. The standard notes that deviations may occur due to ethnic and national-geographic deviations and for people who are sick or disabled. It applies to healthy men and women. Children are not

considered. The standard applies to indoor environments where steady state thermal comfort or moderate deviations from comfort occur. This allows for interpretation and judgement. Does the standard apply to environments where conditions vary? Can the PMV index be used as an adaptive model as it can account for changes in clothing, activity, posture and environmental conditions? The draught rating model is limited in scope to a narrow range of conditions and for people in thermal neutrality. People who are hot or cold may respond differently from the predictions of the draught rating model.

Section B
Calculations Ventilation Rate (ACPH) = Volume flow rate / Volume of domain Velocity or air from exhaust axial fan = CFM / Area Air volume of fan cmh, convert to m3/s and then divide by area to get the velocity of the fan.