Technical FAQs General Which operating system is required to run TileFlow? How does TileFlow calculate the airflow patterns and temperature/pressure distributions?   How can we calculate the airflow requirement (CFM) from a known heat load? Can we use TileFlow to study failure scenarios? How can we represent non-rectangular floors? Does TileFlow account for the change in air density with altitude?   Leakage Flow How can we estimate the distributed leakage area for our raised floor?   Perforated Tiles and Tile Styles How can we estimate the open area of a perforated tile? What is K factor? For our perforated tiles, the manufacturer has given us a graph of pressure drop vs. flow rate. How can we use this information to create a Perforated Tile Style? How do we include cable openings in our simulations? How can we represent perforated tiles with specified airflow rates?   CRAC Units and CRAC Styles How does TileFlow estimate the flow rate through a CRAC unit? How can we add a turning vane (scoop) on a CRAC unit? Can we use TileFlow to study failure scenarios? What is meant by a failed CRAC unit? Does it indicate that the fan/blower is off or the cooling is off? Does TileFlow calculate the backflow through a failed CRAC unit? TileFlow CRAC database does not include our CRAC unit. Can we add it to the database? The CRAC manufacturer installed a customized fan package in our units. How can we model such units in TileFlow?   Server Racks and Server Rack Styles What heat load should we specify in the rack style? Should it be the nameplate power? In some of our racks, the hot air is exhausted from the top face instead of the rear face. Can we define such racks in TileFlow? How do we determine the airflow requirement of our racks? Does TileFlow report the rack inlet and exhaust temperatures?   Under-Floor Blockages How do we account for the effect of pipes and cables present in the plenum? Can we use partitions to control the flow?   Plots and Animation How do we print the color plots? Can we export the color plots to other applications? How can we change the minimum and maximum contour levels in the contour plots? How can we change the range of flow rates (or cooling capacities) in the bar charts? Can we print/save the 3D pictures and animations? Can we make a video of the animations?   Data Exchange Can we export the calculated airflow rates through perforated tiles to Microsoft Excel?   General Which operating system is required to run TileFlow? TileFlow runs on any Windows operating system Back to Top How does TileFlow calculate the airflow patterns and temperature/pressure distributions? TileFlow uses the technique of Computational Fluid Dynamics (CFD), which involves the solution of the mathematical equations governing the physical processes of interest. Back to top How can we calculate airflow requirement (CFM) from a known heat load? The airflow requirement depends on the acceptable temperature rise as air traverses through the computer unit. For air inlet temperature of 55 deg. F and a temperature rise of 20 deg. F, the required cooling airflow rate (CFM) can be calculated as:        CFM = 154 x heat load (kW) This expression is valid at sea level and must be modified for higher altitudes. Back to top Can we use TileFlow to study failure scenarios? Yes. You can investigate scenarios with one or more CRAC units turned off (failed). To turn off a CRAC unit, select the unit and click Turn Off CRAC Unit button on the toolbar. A red cross on the CRAC unit indicates a failed unit. To turn on a failed unit, select the unit and click the same button on the toolbar. Back to top How can we represent non-rectangular floors? You can combine no-flow regions and thin partitions to create floors that are not rectangular. For example, you can create L-shaped or T-shaped floors by using no-flow regions to represent the spaces that are outside the raised floor. This procedure is illustrated in Examples 9 through 14 in the set of illustrative examples supplied with TileFlow. Similarly, you can use thin partitions to represent inclined and curved boundaries. This feature is illustrated in Example 10 (curved bottom boundary) and Example 11 (triangular cutout at the lower-left corner).  Back to top Does TileFlow account for the change in air density with altitude? Yes. TileFlow calculates the density of cooling air using the local atmospheric pressure, which depends on the altitude of the data-center location. The air density affects the cooling capacity of air and the pressure under the raised floor. The altitude is specified using the Operating Conditions command available through the Floor Design menu. The altitudes of selected cities in US are available in the TileFlow on-line help and the User’s manual. Back to top   Leakage Flow How can we estimate distributed leakage area for our raised floor? The distributed leakage area refers to the area of the gaps between the floor panels. It depends on the quality of floor installation and wear and tear. To estimate the leakage area, we need to estimate the average width of the gaps between the panels. A rough estimate of the gap width can be obtained by measuring the distance across a large number of panels, say 20. If there were no gaps between the panels, this distance would be 40 ft; however, because of the gaps, the distance would be larger than 40 ft. The extra distance (beyond 40 ft) divided by 20 is the average width of the gap. Such measurements should be made in different sections of the floor to obtain an average gap width. Let us assume that this width is w inch and your data center has M (2 ft x 2 ft) panels along the length and N panels along the width. The leakage area (sq ft) = 4 x M x N x w/12 Total floor area (sq ft) = 4 x M x N Percentage leakage area = 4 x M x N x (w/12) x 100 /(4 x M x N) = 100 x w/12 Example: If the average gap width is 1/80 in, the percentage leakage area = 0.1% (This estimate does not account for the gaps created due to deteriorating structure and the wear and tear of the panels. The actual leakage area will be larger than the estimate obtained using the procedure outlined here.) Back to top   Perforated Tiles and Tile Styles How can we estimate the open area of a perforated tile? You can estimate the open area by determining the average area of a hole and the number of holes. To determine the area of a hole, measure the diameters of a number of holes and calculate the average value. The percentage open area is given by: Percent open area = N x 0.785 x d2 x 100/576 Here N is the number of holes and d is the hole diameter in inch. Back to top What is K factor? K factor or the loss coefficient is defined as K = Dp / (0.5 r V2), where Dp is the pressure drop, r is the fluid density, and V is the approach velocity. It is a dimensionless number representing the flow resistance. For a standard 25% open perforated tile, the K factor is about 42. Back to top For our perforated tiles, the manufacturer has given us the graph of pressure drop vs. flow rate. How can we use this information to create a Perforated Tile Style? You can use a utility like the Microsoft Excel to fit a polynomial through the data points in the graph and obtain the coefficients of the polynomial. You can then use this relationship to define a new Perforated Tile Style; select the polynomial expression to specify the flow resistance of the perforated tile and enter the values of the relevant coefficients. For perforated tiles, the pressure drop usually varies as the square of the flow rate. Thus, instead of using a curve-fit program, you can calculate the coefficient of the quadratic term as the ratio of the pressure drop and the square of the corresponding flow rate. You should calculate this coefficient for a few points on the curve and use an average value. Note that if the relationship is exactly quadratic, this coefficient will have the same value at all points on the curve. Back to top How do we include cable openings in our simulations? The cable openings are treated just like the perforated tiles. (Both cable openings and perforated tiles are escape routes for the cold air from the plenum to the computer space above the raised floor.) You can create Perforated Tile Styles based on the open area of the cable openings and apply these styles to the desired tiles. To create a Perforated Tile Style for a cutout, follow these steps: 1. Select Edit Perforated Tile Styles command from the Database menu. The Perforated Tile Style Properties dialog appears. 2. Select thow you want to create a new style.   A tile style can be added by creating a new style from scratch or by modifying an existing style. If you want to create the new style from scratch, select New. A style with the name “New Style nn (where nn is a number)” appears at the end of the style list.   If you want to modify an existing style, select the style to be modified from the list of styles and then select Duplicate. A style with the name “Copy of the style name (where style name is the name of the style duplicated)” appears at the end of the style list. 3. Specify the desired style name, texture, and color. 4. In the section Flow Resistance of Perforated Tile/Cutout, select Known Open Area, then select Large Openings: Actual Open Area, and specify the open area in sq in. 5. Click OK. Back to top How can we represent perforated tiles with specified airflow rates? You represent perforated tiles with specified flow rates via Perforated Tile Styles with Known CFM. To create such a style, select Edit Perforated Tile Styles, click New, specify the desired name and color, click Knwon CFM radio button under Additional Resistance (Dampers, Fans, etc.), and specify the desired flow rate through the perforated tile. You can now apply this style to the desired tiles on the raised floor. The Known CFM style can be used to represent any device with a powerful fan (e.g., a rack with an exhaust fan). When the fan is powerful, the device delivers nearly the same flow rate, independent of the local pressure under the raised floor. Back to top   CRAC Units and CRAC Unit Styles How does TileFlow estimate the flow rate through a CRAC unit? TileFlow treats a CRAC unit as a fixed flow rate device. The flow rate is assumed to be the same as the rated flow rate and is specified as part of the input for CRAC unit style. (Theoretically, the flow rate depends on the pressure in the plenum, and it must be calculated using a performance curve, which provides the relationship between the flow rate and the total pressure drop across the CRAC unit assembly. However, in a CRAC unit, the total pressure drop is nearly constant, independent of the pressure in the plenum, as much of the pressure drop occurs within the unit itself. As a result, the flow rate through a CRAC unit is insensitive to the pressure levels in the plenum and stays close to the rated value.) Back to top How can we add a turning vane (scoop) on a CRAC unit? To include turning vane on a CRAC unit, simply select the unit and click Install Turning Vane button on the toolbar. You will see a black line on the CRAC unit, indicating the presence of turning vane. To remove turning vane, select the CRAC unit and click the same button on the toolbar; the black line will be removed. Back to top Can we use TileFlow to study failure scenarios? Yes. You can investigate scenarios with one or more CRAC units turned off (failed). To turn off a CRAC unit, select the unit and click Turn Off CRAC Unit button on the toolbar. A red cross on the CRAC unit indicates a failed unit. To turn on a failed unit, select the unit and click the same button on the toolbar. Back to top What is meant by a failed CRAC unit? Does it indicate that the fan/blower is off or the cooling is off? In TileFlow, a failed CRAC unit means that fan/blower is off and the unit does not supply cold air. Back to top Does TileFlow calculate the backflow through a failed CRAC unit? No. We assume that the flow resistance from the backflow is quite large. The rate of back flow will usually be small. Back to top TileFlow CRAC Style database does not include our CRAC unit. Can we add it to the database? Yes. To add your CRAC unit to the database, follow these steps: 1.     Select Edit CRAC Style command from the Database menu. The CRAC Style Properties dialog appears. 2.     Select the desired option. A CRAC style can be added by creating a new style from scratch or by modifying an existing style. If you want to create the new style from scratch, select New. A style with the name “New Style nn (where nn is a number)” appears at the end of the style list.   If you want to modify an existing style, select the style to be modified from the list of styles and then select Duplicate. A style with the name “Copy of the style name (where style name is the name of the style duplicated)” appears at the end of the style list. You can edit the style name and give name of your choice. 3.     Specify values for different quantities. 4.     Click OK. Back to top The CRAC manufacturer installed a customized fan package in our units. How can we model such units in TileFlow? The installation of a customized fan package affects the flow rate delivered by the CRAC unit. Thus the actual flow rate will be different from the rated flow rate. You can add your CRAC unit as a user-defined CRAC style with the correct flow rate. For the steps to be followed, see answer to the question: TileFlow CRAC Style database does not include our CRAC unit. Can we add it to the database? Back to top Server Racks and Server Rack Styles What heat load should we specify in the rack style? Should it be the nameplate power? The heat load should be the actual heat load in the rack. The nameplate power of a server is the maximum power rating of the server and is not a good representation of the actual power dissipation (or heat load). The nameplate power can be substantially larger than the true heat load. Back to Top In some of our racks, the hot air is exhausted from the top face instead of the rear face. Can we define such racks in TileFlow? Yes. TileFlow allows for five types of airflow configurations for racks. These are: Front to rear Front to rear and top Bottom to top Front, rear, bottom to top Front to rear and top   Back to Top How do we determine the airflow requirement of our racks? To get reliable value for the airflow requirement, you should contact the manufacturer(s) of the servers in the rack. However, in many cases, it may not be possible, and TileFlow provides two alternative methods for estimating the airflow rates.   The TileFlow estimate of the airflow rate is based on the specified value of heat load in the rack and a relationship between the heat load and temperature rise across the server, obtained from available data for a large number of servers. Instead of specifying the airflow rate, you can specify the temperature rise across the rack. TileFlow will calculate this required airflow rate based on the heat load and this temperature rise. Back to Top Does TileFlow report the rack inlet and exhaust temperatures? After calculating the above-floor airflow and temperatures, the Inspect Tool reports the range of inlet and ehaust temperatures for eack rack. Back to Top Under-Floor Blockages How do we account for the effect of pipes and cables present in the plenum? You represent pipes and cables as blockages at specified locations. TileFlow automatically accounts for the blockage effect and flow resistance of the blockages. The blockages can be rectangular, circular, or (thin) partitions. Back to top Can we use partitions to control the flow? Yes. Partitions provide one possible way of modifying the pressure distribution under the raised floor and hence the airflow distribution of the cooling air. You can use partitions to change the flow velocity and to modify the airflow path. TileFlow allows you to place perforated partitions. Thus, by placing partitions at strategic locations and choosing appropriate level of perforations, you are able to obtain the desired distribution of flow rate through perforated tiles. The use of perforated partitions for controlling airflow is illustrated in Example 8 of the set of illustrative examples supplied with TileFlow. Back to top Plots and Animation How do we print the color plots? To print the plot you see on the screen, select Print from the File menu and specify the name of your color printer. Back to top Can we export the color plots to other applications? Yes. You can save the plots as files in various file formats (bmp, jpeg, png, and tiff). To save a plot, click the Save Plot button on the Quick Access menu. Back to top How can we change the minimum and maximum contour levels in the contour plots? TileFlow contains contour plots for airflow rates, cooling capacities, and under-floor pressures. For each plot, TileFlow determines the minimum and maximum values based on the calculated results. For certain situations, you may want to change these values. For examples, when studying failure scenarios for a specific layout, you may wish to use the same range of values for different scenarios. To change the range of contour levels for a plot, follow these steps: Go to the plot you want  to modify. Click the Contour Levels button on the Quick-Access dialog box. The Enter Contour Level Range dialog box appears. Click Custom Levels and specify the minimum and maximum level values. Back to top