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Will turn www.example.com into [URL]http://www.example.com[/URL].
there are so many online psychrometric calculators (hvac-calculators)!
great site Originally Posted by agross I am trying to enable a piece of equipment through a dry bulb temp and %rh... is there an equation that can take the db and rh and convert it to a wet bulb?? thanks, adam. call up "aggreko, cooling tower sizing tool and wet bulb calculator" just plug in d.b. and r.h. you will get wet bulb and enthalpy. keep this on your p.c.
great site
Originally posted by agross Yes, I'm trying to... we have an old plate and frame that was used for free cooling... apparently when they switched over control systems (Barber-Coleman to Siemens) the new actuators/programming were not included for it, only the chillers and cooling tower. This was well before I started working there so I really don't know all the specifics. Anyway, we had to replace an isolation valve on one of the chillers so we manually switched over to the plate and frame and it worked beautifully, chilled water temps held better than expected. My new goal is to convince my boss that we should use it when OAT & RH are favorable. In order to do so, he wants a sequence of operations and a program. This particular chilled water system supports some critical equipment so there is no room for error. I did some research on plate and frame free cooling I found out that you can only use it when WB is 10F less than desired chilled water temp; because we only have OAT & RH sensors, I need to find a way to calculate the WB. Thanks for all the help, Adam. I'll give it a try to post the text version of the Basic code I mentioned before. It's written in RapidQ Basic, but that version is generic enough so that the code should be easily converted to most any programming language. I know it took me very little time to convert it from the original VBA to Java Script, and equally little time to convert it to RapidQ. Originally I'd written it in old DOS QBasic, but have lost the original source code somewhere among a pile of old, archived code on CDs I've got piled up. Which I have intended to catalog, for years, but have never seemed to get around to it. :-) Watch out for line wrap .... 'Just a little routine to calculate the Psychrometric properties 'of air given 3 known conditions. ' 'Given Dry Bulb Temperature, Relative Humidity, and Altitude of a 'location. The routine calculates 8 other properties of the air 'sample. Results can be saved. Mostly useful to HVAC types (Heating 'Ventilation and Air Condicitoning), engineers, science students, etc. ' 'I'd originally written this in another programming language but a 'friend, who is learning to program in RapidQ asked me for an 'an example program in RapidQ that used some simple functions he was 'trying to grasp how to do. ie How to implement math functions, simple 'input boxes, buttons, etc. And how to save a simple text file. ' 'I'm no real programmer, nor expert by any means with RapidQ, so nothing 'here for any experienced programmer to find useful. ' 'However, I thought perhaps a beginner might find some use in my simple 'style and techniques. Or perhaps someone will find the math functions 'for deriving the various other properties of air from the given 3 to 'be of use. ' 'Free for anyone to use as he or she sees fit. 'Bob G - Osiyo53@yahoo.com $Include "Rapidq.inc" DECLARE sub calculate_drha DECLARE Sub Closemain DECLARE Sub Dummyproc DECLARE Sub reset_form DECLARE Sub save_file DIM inout_label_Font AS Qfont inout_label_Font.Name = "MS Sans Serif" inout_label_Font.Size = 8 inout_label_Font.Color = clWindowText inout_label_Font.AddStyles(fsBold,fsUnderLine) DIM Label1_Font AS QFont Label1_Font.Name = "MS Sans Serif" Label1_Font.Size = 8 Label1_Font.Color = clWindowText Label1_Font.AddStyles(fsBold) DIM SaveDialog AS QSAVEDIALOG SaveDialog.Filter = "Text Files(*.TXT)|*.TXT|All Files(*.*)|*.*" SaveDialog.FilterIndex = 1 '' Use "Text Files" as default DIM file1 AS QFILESTREAM DIM a1 AS DOUBLE DIM a2 AS DOUBLE DIM a3 AS DOUBLE DIM a4 AS DOUBLE DIM a5 AS DOUBLE DIM a6 AS DOUBLE DIM acc AS DOUBLE DIM atm AS DOUBLE DIM b1 AS DOUBLE DIM b2 AS DOUBLE DIM b3 AS DOUBLE DIM b4 AS DOUBLE DIM db AS DOUBLE DIM dp AS DOUBLE DIM dx AS DOUBLE DIM elev AS DOUBLE DIM fmid AS DOUBLE DIM h AS DOUBLE DIM j AS DOUBLE DIM nn AS DOUBLE DIM p1 AS DOUBLE DIM p2 AS DOUBLE DIM p3 AS DOUBLE DIM p4 AS DOUBLE DIM psat AS DOUBLE DIM pvp AS DOUBLE DIM pvs AS DOUBLE DIM rh AS DOUBLE DIM rhpercent AS DOUBLE DIM rtb AS DOUBLE DIM savename AS STRING DIM ta AS DOUBLE DIM v AS DOUBLE DIM vp AS DOUBLE DIM w AS DOUBLE DIM wb AS DOUBLE DIM wh AS DOUBLE DIM ws AS DOUBLE DIM wsat AS DOUBLE DIM wstar AS DOUBLE DIM wtemp AS DOUBLE DIM xmid AS DOUBLE DIM y AS DOUBLE DIM z AS DOUBLE '--------------------------------------------------- ' Calculate the Logarithm of a number to the base 10 ' FUNCTION log10(number AS DOUBLE)AS DOUBLE log10 = Log(number) / Log(10#) END FUNCTION '--------------------------------------------------- ' Calculate Atmospheric pressure given elevation ' FUNCTION psychro_atm(elev AS DOUBLE)AS DOUBLE Dim el(21)AS DOUBLE, press(21)AS DOUBLE 'Altitude Press. el(1) = -1000: press(1) = 31.02 el(2) = -500: press(2) = 30.47 el(3) = 0: press(3) = 29.921 el(4) = 500: press(4) = 29.38 el(5) = 1000: press(5) = 28.86 el(6) = 2000: press(6) = 27.82 el(7) = 3000: press(7) = 26.82 el(8) = 4000: press(8) = 25.82 el(9) = 5000: press(9) = 24.9 el(10) = 6000: press(10) = 23.98 el(11) = 7000: press(11) = 23.09 el(12) = 8000: press(12) = 22.22 el(13) = 9000: press(13) = 21.39 el(14) = 10000: press(14) = 20.48 el(15) = 15000: press(15) = 16.89 el(16) = 20000: press(16) = 13.76 el(17) = 30000: press(17) = 8.9 el(18) = 40000: press(18) = 5.56 el(19) = 50000: press(19) = 3.44 el(20) = 60000: press(20) = 2.14 i = 1 WHILE elev > el(i) i = i + 1 WEND psychro_atm = press(i) END FUNCTION '------------------------------------------------------------------------------- ' Calculate vapor pressure at saturation given dry bulb temp ' FUNCTION psychro_pvs(temp AS DOUBLE)AS DOUBLE a1 = -7.90298 a2 = 5.02808 a3 = -0.00000013816 a4 = 11.344 a5 = 0.0081328 a6 = -3.49149 b1 = -9.09718 b2 = -3.56654 b3 = 0.876793 b4 = 0.0060273 ta = (temp + 459.688) / 1.8 IF ta > 273.16 THEN z = 373.16 / ta p1 = (z - 1) * a1 p2 = log10(z) * a2 p3 = ((10 ^ ((1 - (1 / z)) * a4)) - 1) * a3 p4 = ((10 ^ (a6 * (z - 1))) - 1) * a5 ELSE z = 273.16 / ta p1 = b1 * (z - 1) p2 = b2 * log10(z) p3 = b3 * (1 - (1 / z)) p4 = log10(b4) END IF psychro_pvs = 29.921 * (10 ^ (p1 + p2 + p3 + p4)) END FUNCTION '------------------------------------------------------------------------------- ' Calculate Humidity Ratio given dry bulb temp, relative humidity, and elevation ' FUNCTION psychro_wrh(db AS DOUBLE, rh AS DOUBLE, atm AS DOUBLE)AS DOUBLE wsat = psychro_pvs(db) wtemp = 0.62198 * (wsat / (atm - wsat)) psychro_wrh = rh * wtemp END FUNCTION '------------------------------------------------------------------------------- 'Calculate Enthalpy given dry bulb temp and Humidity Ratio ' FUNCTION psychro_h_w(db AS DOUBLE, w AS DOUBLE)AS DOUBLE psychro_h_w = (db * 0.24) + (1061 + (0.444 * db))* w END FUNCTION '------------------------------------------------------------------------------- 'Calculate dew point temp. given Vapor Pressure ' FUNCTION psychro_dp(pvp AS DOUBLE) AS DOUBLE nn=pvp*0.491154 y = LOG(nn) IF pvp < 0.18036 THEN psychro_dp = 90.12 + (26.142 * y) + (0.8927 * y * y) ELSE psychro_dp = 100.45 + (33.193 * y) + (2.319 * y * y) + 0.17074*(y^3)+1.2063*((pvp*0.491154)^0.1984) END IF END FUNCTION '------------------------------------------------------------------------------- 'Calculate Humidity Ratio given dry bulb temp and pressure ' FUNCTION psychro_w_pvp(pair AS DOUBLE, pvp AS DOUBLE) AS DOUBLE psychro_w_pvp = 0.622 * pvp / pair END FUNCTION '------------------------------------------------------------------------------- ' Calculate Vapor Pressure given dry bulb temp, wet bulb temp, and pressure ' FUNCTION psychro_pv1(db AS DOUBLE, wb AS DOUBLE, atm AS DOUBLE) AS DOUBLE pvp = psychro_pvs(wb) ws = (pvp / (atm - pvp)) * 0.62198 IF wb <= 32 THEN wh=((1219.98+0.44*db-0.49*wb)*ws-0.24*(db-wb))/(1219.98+0.44*db-0.49*wb) psychro_pv1 = atm * (wh / (0.62198 + wh)) ELSE wh=((1093-0.556*wb)*ws-0.24*(db-wb))/(1093+0.444*db-wb) psychro_pv1 = atm * (wh / (0.62198 + wh)) END IF END FUNCTION '------------------------------------------------------------------------------- 'Calculate Humidity Ratio given dry bulb temp, wet bulb temp, and pressure ' FUNCTION psychro_w(db AS DOUBLE, wb AS DOUBLE, atm AS DOUBLE) AS DOUBLE vp = psychro_pv1(db, wb, atm) psychro_w = 0.622 * vp / (atm - vp) END FUNCTION '------------------------------------------------------------------------------- 'Computes wet-bulb temperature iteratively, dry bulb, dew point 'enthalpy and atm pressure using Bisection method. ' FUNCTION wet_bulb(db AS DOUBLE,dp AS DOUBLE,h AS DOUBLE,atm AS DOUBLE)AS DOUBLE j=0 acc=0.0001 rtb=dp dx=db-dp WHILE j<40 j=j+1 dx=dx*0.5 xmid=rtb+dx psat=psychro_pvs(xmid) wstar=psychro_w_pvp(atm-psat, psat) fmid=psychro_h_w(xmid, wstar) IF ((h-fmid)>0.0)THEN rtb=xmid END IF IF ABS(dx)<acc THEN EXIT WHILE END IF WEND wet_bulb=rtb wb=rtb END FUNCTION '------------------------------------------------------------------------------- 'Calculate Specific Volume given dry bulb temp, wet bulb temp, and pressure ' FUNCTION psychro_v(db AS DOUBLE, wb AS DOUBLE, atm AS DOUBLE)AS DOUBLE psychro_v = ((0.754 * (db + 459.7)* (1 + (7000 * psychro_w(db, wb, atm) / 4360))) / atm) END FUNCTION CREATE MainForm AS QForm Caption = "Bob G's (Osiyo) Free Software" Top = 129 Left = 203 Width = 460 Height = 343 Center Wndproc=Dummyproc Onclose=Closemain END CREATE CREATE main_label AS QLabel Parent = MainForm Top = 3 Left = 93 Width = 32 Height = 13 Caption = "Calculate Psychrometric Properties of Air" Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE db_label AS QLabel Parent = MainForm Top = 51 Left = 22 Width = 32 Height = 13 Caption = "Dry Bulb Temp (F) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE rh_label AS QLabel Parent = MainForm Top = 75 Left = 5 Width = 109 Height = 13 Caption = "Relative Humidity (%) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE elev_label AS QLabel Parent = MainForm Top = 98 Left = 7 Width = 32 Height = 13 Caption = "Elev Above Sea (FT) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE input_label AS QLabel Parent = MainForm Top = 30 Left = 51 Width = 32 Height = 13 Caption = "INPUTS" Color = &hC0C0C0 Font = inout_label_Font AutoSize = False END CREATE CREATE calc_btn AS QButton Parent = MainForm Top = 72 Left = 238 Width = 75 Height = 25 Caption = "CALCULATE" OnClick = calculate_drha END CREATE CREATE reset_btn AS QButton Parent = MainForm Top = 72 Left = 358 Width = 75 Height = 25 Caption = "RESET" OnClick = reset_form END CREATE CREATE db_edit AS QEdit Parent = MainForm Top = 48 Left = 136 Width = 49 Height = 21 Text = "70.0" Color = &hFFFFFF MaxLength = 5 AutoSize = False END CREATE CREATE rh_edit AS QEdit Parent = MainForm Top = 72 Left = 136 Width = 49 Height = 21 Text = "50.0" Color = &hFFFFFF MaxLength = 5 END CREATE CREATE elev_edit AS QEdit Parent = MainForm Top = 96 Left = 135 Width = 49 Height = 21 Text = "1000" Color = &hFFFFFF MaxLength = 6 END CREATE CREATE output_label AS QLabel Parent = MainForm Top = 129 Left = 182 Width = 32 Height = 13 Caption = "OUTPUTS" Color = &hC0C0C0 Font = inout_label_Font AutoSize = False END CREATE CREATE atm_label AS QLabel Parent = MainForm Top = 154 Left = 18 Width = 32 Height = 13 Caption = "Atmospheric Press (in.Hg) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE svp_label AS QLabel Parent = MainForm Top = 179 Left = 6 Width = 32 Height = 13 Caption = "Saturated Vap Press (in.Hg) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE pvp_label AS QLabel Parent = MainForm Top = 202 Left = 25 Width = 32 Height = 13 Caption = "Partial Vap Press (in.Hg) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE hr_label AS QLabel Parent = MainForm Top = 226 Left = 44 Width = 32 Height = 13 Caption = "Humidity Ratio (lb/lb) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE atm_edit AS QEdit Parent = MainForm Top = 150 Left = 179 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE svp_edit AS QEdit Parent = MainForm Top = 174 Left = 179 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 ReadOnly = True AutoSize = False END CREATE CREATE pvp_edit AS QEdit Parent = MainForm Top = 199 Left = 179 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 ReadOnly = True AutoSize = False END CREATE CREATE hr_edit AS QEdit Parent = MainForm Top = 223 Left = 178 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE svol_label AS QLabel Parent = MainForm Top = 154 Left = 250 Width = 32 Height = 13 Caption = "Specific Vol (cuft/lb) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE dp_label AS QLabel Parent = MainForm Top = 179 Left = 291 Width = 32 Height = 13 Caption = "Dew Point (F) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE wb_label AS QLabel Parent = MainForm Top = 202 Left = 297 Width = 32 Height = 13 Caption = "Wet Bulb (F) : " Color = &hC0C0C0 Font = Label1_Font AutoSize = False END CREATE CREATE ent_label AS QLabel Parent = MainForm Top = 227 Left = 266 Width = 32 Height = 13 Caption = "Enthalpy (BTU/lb) : " Color = &hC0C0C0 Font = Label1_Font END CREATE CREATE svol_edit AS QEdit Parent = MainForm Top = 150 Left = 383 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE dp_edit AS QEdit Parent = MainForm Top = 175 Left = 382 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE wb_edit AS QEdit Parent = MainForm Top = 200 Left = 382 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE ent_edit AS QEdit Parent = MainForm Top = 225 Left = 381 Width = 49 Height = 21 Text = "0.0" Color = &hFFFFFF MaxLength = 7 AutoSize = False ReadOnly = True END CREATE CREATE file_btn AS QButton Parent = MainForm Top = 264 Left = 176 Width = 75 Height = 25 Caption = "Save to File" OnClick = save_file END CREATE MainForm.ShowModal '------------------------------------------------------------------------------- 'Compute other properties given Dry Bulb Temp.,Relative Humidity and Altitude. ' SUB calculate_drha db=VAL(db_edit.Text) elev=VAL(elev_edit.Text) rhpercent=VAL(rh_edit.Text) rh=rhpercent/100 'calc atmospheric pressure atm=psychro_atm(elev) atm_edit.Text = LEFT$((STR$(atm)),7) 'calc vapor pressure at saturation pvs=psychro_pvs(db) svp_edit.Text = LEFT$((STR$(pvs)),7) 'Calculate Partial Vapor Pressure. pvp=pvs*rh pvp_edit.TEXT = LEFT$((STR$(pvp)),7) 'calc humidity ratio w=psychro_wrh(db, rh, atm) hr_edit.Text = LEFT$((STR$(w)),7) 'calculate Enthalpy h=psychro_h_w(db, w) ent_edit.TEXT = LEFT$((STR$(h)),7) 'calculate Dew Point. dp=psychro_dp(pvp) dp_edit.Text = LEFT$((STR$(dp)),7) 'Calculate wet bulb temperature using an iterative method. IF rh <1.000 THEN wb=wet_bulb(db,dp,h,atm) ELSE wb=db END IF wb_edit.Text = LEFT$((STR$(wb)),7) 'calculate Specific Volume v=psychro_v(db, wb, atm) svol_edit.Text = LEFT$((STR$(v)),7) END SUB SUB Dummyproc ' To Minimize Properly END SUB SUB Closemain Application.Terminate END SUB SUB reset_form db_edit.Text = "70.0" elev_edit.Text = "1000" rh_edit.Text = "50.0" atm_edit.Text = "0.0" svp_edit.Text = "0.0" pvp_edit.TEXT = "0.0" hr_edit.Text = "0.0" ent_edit.TEXT = "0.0" dp_edit.Text = "0.0" wb_edit.Text = "0.0" svol_edit.Text = "0.0" END SUB SUB save_file IF SaveDialog.Execute THEN savename = SaveDialog.FileName IF UCASE$(RIGHT$(savename,4))<>".TXT" THEN savename = savename + ".TXT" END IF sl1$ = "Dry Bulb Temp (F) : " + db_edit.Text sl2$ = "Relative Humidity (%) : " + rh_edit.Text sl3$ = "Elev Above Sea (FT) : " + elev_edit.Text sl4$ = "Atmospheric Press (in.Hg) : " + atm_edit.Text sl5$ = "Saturated Vap Press (in.Hg) : " + svp_edit.Text sl6$ = "Partial Vap Press (in.Hg) : " + pvp_edit.TEXT sl7$ = "Humidity Ratio (lb/lb) : " + hr_edit.Text sl8$ = "Specific Vol (cuft/lb) : " + svol_edit.Text sl9$ = "Dew Point (F) : " + dp_edit.Text sl10$ = "Wet Bulb (F) : " + wb_edit.Text sl11$ = "Enthalpy (BTU/lb) : " + ent_edit.TEXT file1.Open(savename,fmCreate) ' create a new file file1.WriteLine("Inputs Used ..............................") file1.WriteLine("") file1.WriteLine(sl1$) file1.WriteLine(sl2$) file1.WriteLine(sl3$) file1.WriteLine("") file1.WriteLine("") file1.WriteLine("Calculated Results .......................") file1.WriteLine("") file1.WriteLine(sl4$) file1.WriteLine(sl5$) file1.WriteLine(sl6$) file1.WriteLine(sl7$) file1.WriteLine(sl8$) file1.WriteLine(sl9$) file1.WriteLine(sl10$) file1.WriteLine(sl11$) file1.WriteLine("") file1.Close END IF END SUB 'End Program
Originally posted by schoolguy Here is a good one: X = 273.16 / ((DryBulb - 32) / 1.8 + 273.16) X = -10.7959 * (1 - X) - (2.1836 * ln(X)) + 2.2196 X = 29.92 * (1 / exp(2.3026 * X)) X = RH * X / 100 X = 0.622 * X / (29.92 - X) Enthalpy = (0.24 + (0.444 * X)) * DryBulb + (1061 * X) Not bad, the algorithm gives a pretty decent approximation. I tested it against a known mathematical model and yours gives good results in simpler form. Doesn't correct for altitude, etc but the answers are perfectly useable for ordinary HVAC work. However, you're calculating enthalphy. Original poster requested Wet Bulb. I see that as one works the math, by line #4 above, you extract the partial vapor pressure. That's the X=RH*X/100 line, in case line counting gets confusing due to reformatting of lines on your screen. Now, there is no such thing as a math formula that will give one the EXACT, one and only answer, for Wet Bulb calculations. The only thing math can do is approximate. And as to how close a math algorithm is to the reality of a measured WBT, depends on how complicated one wishes to get with your math. If one is trying to stay fairly simple, once one has worked out the first 4 lines above, you've arrived at Partial Vapor Pressure (close enough for most HVAC purposes)for the given DBT and RH. Using the PVP, find approx Dew Point. nn=pvp*0.491154 y = LOG(nn) IF pvp < 0.18036 THEN dp = 90.12 + (26.142 * y) + (0.8927 * y * y) ELSE dp = 100.45 + (33.193 * y) + (2.319 * y * y) dp = dp + 0.17074*(y^3)+1.2063*((pvp*0.491154)^0.1984) END IF (Watch out for line wrap) From here, one can keep it simple and use the "1/3 Rule" that metrologists often use to approximate WBT. Which gives a fairly decent result under most operating conditions for the equipment the original poster mentions. Under the 1/3 Rule one figures out the Dew Point Depression (DPD), which is the difference between Dry Bulb and Dew Point. Then divide DPD by 3. And subtract that result from Dry Bulb. To be safe, I'd add 1.0 to the WBT answer before doing the subtraction to determine if Desired Coil Temp minus WBT >= 10. Other than that. One just about has to resort to using an iterative mathematical model to extract a more accurate answer. Which is what those electronic meters that read DBT and RH then calculate WBT when yah push a button do. And what I used in the Basic language programming example I pointed to in my original response. That example uses an algorithm published by ASHRAE, that was tested against actual measured values and shown to be accurate enough for HVAC design purposes. Now, if the original poster is looking for a nice, simple X= Y*Z type formula. I'm afraid he's SOL. There is no such simple mathematical formula possible that'll give any sort of meaningful and useful answer.
Yes, I'm trying to... we have an old plate and frame that was used for free cooling... apparently when they switched over control systems (Barber-Coleman to Siemens) the new actuators/programming were not included for it, only the chillers and cooling tower. This was well before I started working there so I really don't know all the specifics. Anyway, we had to replace an isolation valve on one of the chillers so we manually switched over to the plate and frame and it worked beautifully, chilled water temps held better than expected. My new goal is to convince my boss that we should use it when OAT & RH are favorable. In order to do so, he wants a sequence of operations and a program. This particular chilled water system supports some critical equipment so there is no room for error. I did some research on plate and frame free cooling I found out that you can only use it when WB is 10F less than desired chilled water temp; because we only have OAT & RH sensors, I need to find a way to calculate the WB. Thanks for all the help, Adam.
Here is a good one: X = 273.16 / ((DryBulb - 32) / 1.8 + 273.16) X = -10.7959 * (1 - X) - (2.1836 * ln(X)) + 2.2196 X = 29.92 * (1 / exp(2.3026 * X)) X = RH * X / 100 X = 0.622 * X / (29.92 - X) Enthalpy = (0.24 + (0.444 * X)) * DryBulb + (1061 * X)
Agross, are you programming, if you are I have just the thing
Originally posted by osiyo Originally posted by -80guru get a sling psycrometer. It has WB DB and RH True. But then, he asked for the equations. So I presumed he might be writing a program. If he just wants to do the conversion manually, he could also use a standard psychrometric chart. Yes,I was afraid you control guys were talking about something else... here ya go: RH=100e(Tw-Td/28.116)-17.4935(Td-Tw)e-Td/28.116 RH is in percent.Td is dry bulb in F.Tw is wet bulb in F. The symbol e refers to the exponential function.The exponential function is taken to the power represented by the number above the symbol.(The function of e is the usual one used where 2.71828 is the value of e) The formula for grains of water per pound of dry air is: grain/pound=.09065RHeTd/28.116 Now remember that I could only copy that from the book to here in "keyboard style".I think you can decipher it though.
Originally posted by -80guru get a sling psycrometer. It has WB DB and RH True. But then, he asked for the equations. So I presumed he might be writing a program. If he just wants to do the conversion manually, he could also use a standard psychrometric chart.
Originally posted by agross thanks for the input osiyo, i'm having some trouble w/ the link, can you help at all? Okay, try this. Go to the below site. http://groups.yahoo.com/group/rapidq/ You'll have to subscribe to the group to look into the "Files" section. A painless process and costs nothing. They just ask for a valid email address. I've been a subscriber to various Yahoo Groups for years, and near as I can tell they've never passed around my email addy. Nor will they send yah annoying mail unless you allow it. Anyway, subscribe. Takes 30 seconds. Then look into the "Files" section. And you'll see "airpsychro.bas". It's a simple text file. You don't need any special program to view, download, or edit it. I'd just paste it here, however I'm not sure this site would like an 18k text file pasted into their edit box. Plus it'd word wrap in this site's edit box, which would make it hard to read. If that doesn't work, say so. And if you have an available email addy I'll email it direct.
get a sling psycrometer. It has WB DB and RH
thanks for the input osiyo, i'm having some trouble w/ the link, can you help at all?
Originally posted by agross I am trying to enable a piece of equipment through a dry bulb temp and %rh... is there an equation that can take the db and rh and convert it to a wet bulb?? thanks, adam. Do you read the Basic programming language, at least a little? If so, you should find the math formulas you want here: http://f6.grp.yahoofs.com/v1/UM1FQql...AirPsychro.bas It's a Basic program I wrote that'll accept DB, RH, and Altitude inputs, then give you 6 other values as a result. Wet Bulb, Enthalpy, etc. Use it as you wish. Even if you don't understand Basic, it's not hard to follow the code and find the math routines. If yah know basic math, you can understand the formulas. If the link doesn't work for you, let me know and I'll try some other way of getting the text of the file to you.
I am sure there must be an"equation"for this but I sure dont know it...anyway you might want to look at this thread: RH and TEMP conversion chart---- by nicholasa---IAQ section
I am trying to enable a piece of equipment through a dry bulb temp and %rh... is there an equation that can take the db and rh and convert it to a wet bulb?? thanks, adam.
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