<%
# *******************************************************************************
# OpenStudio(R), Copyright (c) Alliance for Sustainable Energy, LLC.
# See also https://openstudio.net/license
# *******************************************************************************
%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
.rhline {
stroke: blue;
stroke-width: 1;
fill: none;
}
.rhtext {
fill: blue;
}
.tdbline {
stroke: green;
stroke-width: 1;
fill: none;
}
.tdbtext {
fill: green;
}
.wline {
stroke: red;
stroke-width: 1;
fill: none;
}
.wtext {
fill: red;
}
.hline {
stroke: black;
stroke-width: 1;
fill: none;
}
.htext {
fill: black;
}
.twbline {
stroke: orange;
stroke-width: 1;
fill: none;
}
.twbtext {
fill: orange;
}
.tdpline {
stroke: dimgray;
stroke-width: 1;
fill: none;
}
.tdptext {
fill: dimgray;
}
.axis path, .axis line {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
.brush .extent {
stroke: #fff;
fill: grey;
fill-opacity: .750;
shape-rendering: crispEdges;
}
.brush .background {
fill: grey;
fill-opacity: .125;
shape-rendering: crispEdges;
}
.grid .tick {
stroke: lightgrey;
opacity: 0.7;
}
.grid path {
stroke-width: 0;
}
.noselect {
-webkit-touch-callout: none;
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
}
</style>
<title>HVAC Psychrometric Chart</title>
<link href="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.2.0/css/bootstrap.css" rel="stylesheet">
<script type="text/javascript" src="http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script type="text/javascript" src="http://cdnjs.cloudflare.com/ajax/libs/d3/3.3.9/d3.min.js"></script>
<script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
</head>
<body>
<div id="psychart" class="container"></div>
<script>
// This variable will be an array of data series to graph
var obj = <%= all_series %>;
$(document).ready(function() {
var elev = 1828; // 6,000 ft
var pc = new PsychrometricChart(elev);
pc.drawChart("#psychart");
var i = 1;
$.each(obj, function(index, all_series) {
var series = obj[index];
pc.addPoints(series, i);
i += 1;
});
});
function PsychrometricChart(elevation) {
// Specify the bounds of the chart // TODO make input params?
this.tdb_min = -23.3; // -10F
this.tdb_max = 48.9; // 120F
this.w_min = 0;
this.w_max = 0.035;
this.elev = elevation;
this.pb = pbFnElev(this.elev);
// Specify the overall size of the chart plus range selector, etc.
this.svgheight = 1000;
this.svgwidth = 1200;
// Setup the margins around the chart and date range selector
this.chartmargin = {
top: 50,
right: 100,
bottom: 70,
left: 100
};
this.selectmargin = {
top: 0,
right: 100,
bottom: 50,
left: 100
};
// Determine the size of the chart and the selector
// based on a fraction of the overall desired size
this.chartheightfrac = 0.7;
this.totalchartheight = this.svgheight * this.chartheightfrac;
this.totalselectheight = this.svgheight * (1 - this.chartheightfrac);
this.chartheight = this.totalchartheight - this.chartmargin.top - this.chartmargin.bottom;
this.selectheight = this.totalselectheight - this.selectmargin.bottom - this.selectmargin.top;
this.chartwidth = this.svgwidth - this.chartmargin.left - this.chartmargin.right;
this.selectwidth = this.svgwidth - this.selectmargin.left - this.selectmargin.right;
this.reflegendheight = this.chartheight / 4;
this.reflegendwidth = this.chartwidth / 4;
// Setup the spacing for the legends
this.legendSpacing = 25;
// Horizontal axis scale SI (C)
this.tdb_extent = [this.tdb_min, this.tdb_max];
this.tdb_scale = d3.scale.linear()
.range([0, this.chartwidth])
.domain(this.tdb_extent);
// Horizontal axis scale IP (F)
this.tdb_extent_F = [10, 120];
this.tdb_scale_F = d3.scale.linear()
.range([0, this.chartwidth])
.domain(this.tdb_extent_F);
// Vertical axis scale SI (C)
this.w_extent = [this.w_min, this.w_max];
this.w_scale = d3.scale.linear()
.range([this.chartheight, 0])
.domain(this.w_extent);
// Generates a line scaled to the x/y axes
this.addLine = d3.svg.line()
.x(function(d) {
return this.tdb_scale(d.tdb);
})
.y(function(d) {
return this.w_scale(d.w);
})
.interpolate("linear");
// Draw the chart, including the reference lines
// and the date range selector
this.drawChart = function(idOfElementToAppendTo) {
// Make an svg area for the chart, including the range selector
this.svg = d3.select(idOfElementToAppendTo)
.append("svg")
.attr("class", "svg-psych").attr("id", "svg-psych")
.attr("height", this.svgheight)
.attr("width", this.svgwidth);
// Make a group for the main chart body
this.chartbody = this.svg.append("g")
.attr("transform", "translate(" + this.chartmargin.left + "," + this.chartmargin.top + ")");
// Make a clipping mask to keep the lines inside the chart body
this.chartbody.append("defs")
.append("clipPath")
.attr("id", "clip")
.append("rect")
.attr("width", this.chartwidth)
.attr("height", this.chartheight);
// Draw the reference lines inside the chart body group
this.draw_w_lines();
this.draw_tdb_lines();
this.draw_h_lines();
this.draw_rh_lines();
this.draw_twb_lines();
this.draw_tdp_lines();
this.draw_rh_mask();
// Temporarily draw the points representing the chart bounds
var corners = {
name: "series 2",
color: "black",
data: [{
tdb: this.tdb_min,
w: this.w_min
}, {
tdb: this.tdb_max,
w: this.w_min
}, {
tdb: this.tdb_min,
w: this.w_max
}, {
tdb: this.tdb_max,
w: this.w_max
}]
};
//this.addPoints(corners);
// Create the horizontal dry bulb temperature (tdb) scale
var tdb_axis = d3.svg.axis().scale(this.tdb_scale);
var tdb_axis_F = d3.svg.axis().scale(this.tdb_scale_F);
// Create the vertical humidity ratio (w) scale
var w_axis = d3.svg.axis().scale(this.w_scale).orient("right");
// Create a group containing tdb axis
this.tdbaxis = this.chartbody.append("g")
.attr("class", "tdb axis")
.attr("id", "tdb-axis-C")
.attr("transform", "translate(0," + (this.chartheight) + ")")
.call(tdb_axis);
// Create a group containing the w axis
this.waxis = this.chartbody.append("g")
.attr("class", "w axis")
.attr("transform", "translate(" + (this.chartwidth) + ",0)")
.call(w_axis);
// Label the tdb axis
this.tdbaxis.append("text")
.text("Dry-bulb Temperature [°C]")
.attr("class", "tdb-unit").attr("id", "tdb-axis-C-label")
.attr("x", (this.chartwidth / 2)) // TODO dynamically account for width of axis label to center
.attr("y", 50);
// Label the w axis
this.waxis.append("text")
.text("Humidity Ratio [kg water/ kg dry air] ")
.attr("transform", "rotate (-90, 0, 0) translate(" + -1 * (this.chartheight / 2) + "," + (this.chartmargin.right / 2 + 10) + ")"); // TODO dynamically account for width of axis label to center
// Create a legend for the data series
this.primlegend = this.chartbody.append("g")
.attr("class", "w axis")
.attr("transform", "translate(" + (this.chartwidth / 3) + ",0)");
this.primlegend.append("text").text("Series Names")
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 1)
.attr("class", "noselect");
// Create a legend for the reference lines
this.legend = this.chartbody.append("g")
.attr("class", "w axis")
.attr("transform", "translate(" + (this.chartmargin.left / 2) + ",0)");
this.legend.append("text").text("Reference Lines (Click to Toggle On/Off)")
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 1)
.attr("class", "noselect");
this.legend.append("text").text("Dry Bulb Temperature")
.on("click", toggletdblines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 2)
.attr("class", "tdbtext noselect");
this.legend.append("text").text("Relative Humidity")
.on("click", togglerhlines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 3)
.attr("class", "rhtext noselect");
this.legend.append("text").text("Humidity Ratio")
.on("click", togglewlines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 4)
.attr("class", "wtext noselect");
this.legend.append("text").text("Enthalpy")
.on("click", togglehlines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 5)
.attr("class", "htext noselect");
this.legend.append("text").text("Wet Bulb Temperature")
.on("click", toggletwblines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 6)
.attr("class", "twbtext noselect");
this.legend.append("text").text("Dew Point Temperature")
.on("click", toggletdplines)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * 7)
.attr("class", "tdptext noselect");
function togglerhlines() {
// Select the reference lines
var refLines = d3.selectAll("path.rhline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
function toggletdblines() {
// Select the reference lines
var refLines = d3.selectAll("path.tdbline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
function togglewlines() {
// Select the reference lines
var refLines = d3.selectAll("path.wline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
function togglehlines() {
// Select the reference lines
var refLines = d3.selectAll("path.hline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
function toggletwblines() {
// Select the reference lines
var refLines = d3.selectAll("path.twbline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
function toggletdplines() {
// Select the reference lines
var refLines = d3.selectAll("path.tdpline");
// Determine if current line is visible
if (refLines.attr("active")) {
refLines.style("display", "none");
refLines.attr("active", null);
} else {
refLines.style("display", "inherit");
refLines.attr("active", true);
}
}
var startDate = Date.parse("2009/01/01 01:00:00"); // TODO pull start and end date from 1st data series
var endDate = Date.parse("2010/01/01 01:00:00");
var startHour = 0;
var endHour = 24;
// Create an x scale for the selector (date range)
this.sel_x_scale = d3.time.scale()
.domain([startDate, endDate])
.range([0, this.selectwidth]);
// Create a y scale for the selector (hour range)
this.sel_y_scale = d3.scale.linear()
.domain([startHour, endHour])
.range([0, this.selectheight]);
var brush = d3.svg.brush()
.x(this.sel_x_scale)
.y(this.sel_y_scale)
.on("brush", brushed);
// Make a group for the selector
this.selector = this.svg.append("g")
.attr("class", "x brush")
.attr("id", "selector")
.attr("transform", "translate(" + this.selectmargin.left + "," + (this.chartmargin.top + this.chartheight + this.chartmargin.bottom + this.selectmargin.top) + ")")
.call(brush);
this.selector.selectAll(".background")
//.attr("height", this.selectheight)
.style("visibility", "visible");
// Create the selector date x axis
var selector_axis = d3.svg.axis().scale(this.sel_x_scale)
.orient("bottom")
.tickFormat(d3.time.format("%b-%d"));
// Create a group containing selector date axis
this.selectoraxis = this.selector.append("g")
.attr("class", "selector axis")
.attr("id", "selector-x-axis")
.attr("transform", "translate(0," + (this.selectheight) + ")")
.call(selector_axis)
.selectAll("text")
.style("text-anchor", "end")
.attr("transform", function(d) {
return "rotate(-65)";
});
// Create the selector time x axis
selector_axis = d3.svg.axis().scale(this.sel_y_scale)
.orient("left");
//.tickFormat(d3.time.format("%H")); // TODO figure out how to format ticks as time
// Create a group containing selector time axis
this.selectoraxis = this.selector.append("g")
.attr("class", "selector axis")
.attr("id", "selector-y-axis")
.call(selector_axis)
.selectAll("text")
.style("text-anchor", "end");
function brushed() {
var s = brush.extent();
var ldb = s[0][0];
var udb = s[1][0];
var ltb = s[0][1];
var utb = s[1][1];
// TODO implement brush snapping on the Y (time) axis of selector
// like seen here: http://bl.ocks.org/mbostock/6232620
console.log("lower date bound =" + ldb + ", upper date bound = " + udb);
console.log("lower time bound =" + ltb + ", upper time bound = " + utb);
// Select all the circles
var circles = d3.selectAll("circle");
// Hide circles before and after selected range
var hiddenCircles = circles.filter(function(d) {
return (Date.parse(d.time) <= ldb || Date.parse(d.time) >= udb);
});
hiddenCircles.style("visibility", "hidden");
// Show circles in the selected range // TODO make this filter function easier to read!
var visibleCircles = circles.filter(function(d) {
return (new Date(d.time) > ldb && new Date(d.time) < udb && new Date(d.time).getHours() > ltb && new Date(d.time).getHours() < utb);
});
visibleCircles.style("visibility", "visible");
}
};
// Make a group for the month buttons
// this.selector = this.svg.append("g")
// .attr("class", "x brush")
// .attr("id", "selector")
// .attr("transform", "translate(" + this.selectmargin.left + "," + (this.chartmargin.top + this.chartheight + this.chartmargin.bottom + this.selectmargin.top) + ")")
// .call(brush);
this.draw_w_lines = function() {
// Draw the horizontal humidity ratio lines
// at .001 intervals
for (var wIter = this.w_min; wIter <= this.w_max; wIter += 0.001) {
var psychLine = [];
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 0.5) {
psychLine.push({
tdb: tdbIter,
w: wIter
});
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "wline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_tdb_lines = function() {
// Draw the vertical dry bulb temperature lines
// at 5F intervals (2.78 delta-C)
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 2.78) {
var psychLine = [];
for (var wIter = this.w_min; wIter <= this.w_max; wIter += 0.001) {
psychLine.push({
tdb: tdbIter,
w: wIter
});
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "tdbline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_rh_lines = function() {
// Calculate the rh lines
// at 10% rh intervals
for (var rhIter = 0; rhIter <= 1; rhIter += 0.1) {
var psychLine = [];
//console.log(rhIter + " %RH")
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 0.5) {
var w = psyWFnTdbRhPb(tdbIter, rhIter, this.pb);
psychLine.push({
tdb: tdbIter,
w: w
});
//console.log("---tdb = " + tdbIter + ", rh = " + rhIter + " => w = " + w)
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "rhline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_h_lines = function() {
// Calculate the enthalpy lines
// at 5Btu/lb dry air (11630 J/kg) intervals
for (var hIter = 15000; hIter <= 139560; hIter += 11630) { // TODO calc min/max h from limits
var psychLine = [];
//console.log("enthalpy (h) = " + hIter)
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 2) {
var w = psyWFnTdbH(tdbIter, hIter);
psychLine.push({
tdb: tdbIter,
w: w
});
//console.log("---tdb = " + tdbIter + ", h = " + hIter + " => w = " + w)
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "hline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_twb_lines = function() {
// Calculate the wetbulb lines
// at 5C intervals
for (var twbIter = 0; twbIter <= 100; twbIter += 1) { // TODO calc min/max h from limits
var psychLine = [];
console.log("twb (C) = " + twbIter);
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 2) {
var w = psyWFnTdbTwbPb(tdbIter, twbIter, this.pb);
psychLine.push({
tdb: tdbIter,
w: w
});
console.log("---tdb = " + tdbIter + ", twb = " + twbIter + " => w = " + w);
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "twbline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_tdp_lines = function() {
// Calculate the dew-point lines
// at 5C intervals
for (var tdpIter = -20; tdpIter <= 100; tdpIter += 1) { // TODO calc min/max h from limits
var psychLine = [];
console.log("tdp (C) = " + tdpIter);
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 2) {
var w = psyWFnTdpPb(tdpIter, this.pb);
psychLine.push({
tdb: tdbIter,
w: w
});
console.log("---tdb = " + tdbIter + ", tdp = " + tdpIter + " => w = " + w);
}
this.chartbody.append("path")
.attr("d", this.addLine(psychLine))
.attr("class", "tdpline")
.attr("active", true)
.attr("clip-path", "url(#clip)");
}
};
this.draw_rh_mask = function() {
// Calculate the rh line at 100%
// and use to make a mask to cover the upper
// left region of the chart
var rhMax = 1;
var psychLine = [];
for (var tdbIter = this.tdb_min; tdbIter <= this.tdb_max; tdbIter += 0.5) {
var w = psyWFnTdbRhPb(tdbIter, rhMax, this.pb);
psychLine.push({
tdb: tdbIter,
w: w
});
//console.log("---tdb = " + tdbIter + ", rh = " + rhMax + " => w = " + w)
}
//var wMax = psyWFnTdbRhPb(tdbIter, , this.pb)
psychLine.push({
tdb: this.tdb_min,
w: this.w_max
});
this.chartbody.append("path") // TODO Change this to a clipping mask instead of a shape with fill
.attr("d", this.addLine(psychLine))
.attr("class", "rhmask")
.attr("clip-path", "url(#clip)")
.attr("stroke", "white") // TODO use CSS to style?
.attr("fill", "white"); // TODO use CSS to style?
};
this.addPoints = function(series, i) {
// Assign this chart to a variable
// so that we can use its info inside the d3 functions
pc = this;
// Add the series name to the legend
this.primlegend.append("text").text(series.name)
.style("cursor", " pointer")
.attr("y", this.legendSpacing * (i + 1))
.attr("class", "noselect")
.style("fill", series.color);
// Add a group to hold the points in the series
var seriesGroup = this.chartbody.append("g")
.attr("class", "psych-series");
var points = seriesGroup.selectAll("circle")
.data(series.data)
.enter()
.append("circle");
var pointAttributes = points.attr("cx", function(d) {
return pc.tdb_scale(d.tdb);
}) //
.attr("cy", function(d) {
return pc.w_scale(d.w);
})
.attr("r", 4)
.style("fill", series.color)
.style("fill-opacity", 0.3)
.append("svg:title")
.text(function(d) {
return d.time + ": Tdb = " + d.tdb.toFixed(1) + "C, W = " + d.w.toFixed(3) + "lb H2O/lb dry air";
});
};
}
// This library of psychrometric calculations was adapted from the EnergyPlus
// psychrometric calculations (C++) which can be found here:
// https://github.com/NREL/EnergyPlus/blob/149f03ea2ce84582828f037faf768892ca674f09/src/EnergyPlus/Psychrometrics.hh
// The calculation methodologies are unchanged, however, the mechanisms for caching
// function results for later use, and the logging of error messages was removed.
var KELVIN_CONV = 273.15;
// PURPOSE OF THIS FUNCTION:
// This function provides barometric pressure as a function
// of elevation.
function pbFnElev(
elev // elevation (Meters)
) {
// FUNCTION INFORMATION:
// AUTHOR Andrew Parker
// DATE WRITTEN Dec 9, 2014
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// A Quick Derivation relating altitude to air pressure
// 2004 Portland State Aerospace Society
// http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf
// Equation 9
var pb = 100 * Math.pow(((44331.514 - elev) / 11880.516), (1 / 0.1902632)); // Barometric Pressure {Pa}
return pb;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the saturation pressure as a function of temperature.
function psyPsatFnTemp(
tdb // dry-bulb temperature {C}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED NA
// RE-ENGINEERED Nov 2003; Rahul Chillar
// METHODOLOGY EMPLOYED:
// Hyland & Wexler Formulation, range -100C to 200C
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 2005, Chap 6 (Psychrometrics), Eqn 5 & 6.
// Compared to Table 3 values (August 2007) with average error of 0.00%, max .30%,
// min -.39%. (Spreadsheet available on request - Lawrie).
// Return value
var pb; // result=> saturation pressure {Pascals}
// Convert temperature from Centigrade to Kelvin.
var tkel = tdb + KELVIN_CONV; // Dry-bulb in REAL(r64) for function passing
// If below -100C,set value of Pressure corresponding to Saturation Temperature of -100C.
if (tkel < 173.15) {
pb = 0.0017;
// If below freezing, calculate saturation pressure over ice.
} else if (tkel < KELVIN_CONV) { // tkel >= 173.15
var C1 = -5674.5359; // Coefficient for TKel < KelvinConvK
var C2 = 6.3925247; // Coefficient for TKel < KelvinConvK
var C3 = -0.9677843e-2; // Coefficient for TKel < KelvinConvK
var C4 = 0.62215701e-6; // Coefficient for TKel < KelvinConvK
var C5 = 0.20747825e-8; // Coefficient for TKel < KelvinConvK
var C6 = -0.9484024e-12; // Coefficient for TKel < KelvinConvK
var C7 = 4.1635019; // Coefficient for TKel < KelvinConvK
pb = Math.exp(C1 / tkel + C2 + tkel * (C3 + tkel * (C4 + tkel * (C5 + C6 * tkel))) + C7 * Math.log(tkel));
// If above freezing, calculate saturation pressure over liquid water.
} else if (tkel <= 473.15) { // tkel >= 173.15 // tkel >= KELVIN_CONV
var C8 = -5800.2206; // Coefficient for TKel >= KelvinConvK
var C9 = 1.3914993; // Coefficient for TKel >= KelvinConvK
var C10 = -0.048640239; // Coefficient for TKel >= KelvinConvK
var C11 = 0.41764768e-4; // Coefficient for TKel >= KelvinConvK
var C12 = -0.14452093e-7; // Coefficient for TKel >= KelvinConvK
var C13 = 6.5459673; // Coefficient for TKel >= KelvinConvK
pb = Math.exp(C8 / tkel + C9 + tkel * (C10 + tkel * (C11 + tkel * C12)) + C13 * Math.log(tkel));
// If above 200C, set value of Pressure corresponding to Saturation Temperature of 200C.
} else { // tkel >= 173.15 // tkel >= KELVIN_CONV // tkel > 473.15
pb = 1555000;
}
return pb;
}
// PURPOSE OF THIS FUNCTION:
// This function provides density of air as a function of barometric
// pressure, dry bulb temperature, and humidity ratio.
function psyRhoAirFnPbTdbW(
pb, // barometric pressure (Pascals)
tdb, // dry bulb temperature (Celsius)
w // humidity ratio (kgWater/kgDryAir)
) {
// FUNCTION INFORMATION:
// AUTHOR G. S. Wright
// DATE WRITTEN June 2, 1994
// MODIFIED na
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// universal gas const for air 287 J/(kg K)
// air/water molecular mass ratio 28.9645/18.01534
// REFERENCES:
// Wylan & Sontag, Fundamentals of Classical Thermodynamics.
// ASHRAE handbook 1985 Fundamentals, Ch. 6, eqn. (6),(26)
var rhoair = pb / (287 * (tdb + KELVIN_CONV) * (1 + 1.6077687 * Math.max(w, 1e-5)));
return rhoair;
}
// PURPOSE OF THIS FUNCTION:
// This function provides latent energy of air as function of humidity ratio and temperature.
function psyHfgAirFnWTdb(
w, // humidity ratio {kgWater/kgDryAir} !unused1208
tdb // input temperature {Celsius}
) {
// FUNCTION INFORMATION:
// AUTHOR Richard Liesen
// DATE WRITTEN May, 2001
// MODIFIED June, 2002
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// calculates hg and then hf and the difference is Hfg.
// REFERENCES:
// see ASHRAE Fundamentals psychrometric Chapter
// USAGE: hfg = psyHfgAirFnWTdb(w,tdb)
// Return value
// result => heat of vaporization for moist air {J/kg}
// This formulation currently does not use W since it returns results that are in J/kg and the
// amount of energy is on a per unit of moisture basis.
tdb = Math.max(tdb, 0); // input temperature {Celsius} - corrected for >= 0C
var hfg = (2500940 + 1858.95 * Temperature) - (4180 * Temperature); // enthalpy of the gas - enthalpy of the fluid
return hfg;
}
// PURPOSE OF THIS FUNCTION:
// This function provides latent energy of the moisture as a gas in the air as
// function of humidity ratio and temperature.
function psyHgAirFnWTdb(
w, // humidity ratio {kgWater/kgDryAir} !unused1208
tdb // input temperature {Celsius}
) {
// FUNCTION INFORMATION:
// AUTHOR Richard Liesen
// DATE WRITTEN May, 2001
// MODIFIED June, 2002
// RE-ENGINEERED na
// REFERENCES:
// see ASHRAE Fundamentals psychrometric Chapter
// USAGE: hg = psyHgAirFnWTdb(w,tdb)
// This formulation currently does not use W since it returns results that are in J/kg and the
// amount of energy is on a per unit of moisture basis.
var hg = 2500940 + 1858.95 * tdb; // enthalpy of the gas {units?}
return hg;
}
// PURPOSE OF THIS FUNCTION:
// This function calculates the enthalpy {J/kg} from dry-bulb temperature and humidity ratio.
function psyHFnTdbW(
tdb, // dry-bulb temperature {C}
w // humidity ratio
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P100, EQN 32
// calculate enthalpy
var h = 1.00484e3 * tdb + Math.max(w, 1e-5) * (2.50094e6 + 1.85895e3 * tdb); // enthalpy {J/kg}
return h;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the heat capacity of air {J/kg-C} as function of humidity ratio.
function psyCpAirFnWTdb(
w, // humidity ratio {kgWater/kgDryAir}
tdb // input temperature {Celsius}
) {
// FUNCTION INFORMATION:
// AUTHOR J. C. VanderZee
// DATE WRITTEN Feb. 1994
// MODIFIED na
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// take numerical derivative of psyHFnTdbW function
// REFERENCES:
// see psyHFnTdbW ref. to ASHRAE Fundamentals
// USAGE: cpa = psyCpAirFnWTdb(w,tdb)
// compute heat capacity of air
w = Math.max(w, 1e-5);
var cpa = (psyHFnTdbW(tdb + 0.1, w) - psyHFnTdbW(tdb, w)) * 10; // result => heat capacity of air {J/kg-C}
return cpa;
}
// PURPOSE OF THIS FUNCTION:
// This function provides air temperature from enthalpy and humidity ratio.
function psyTdbFnHW(
h, // enthalpy {J/kg}
w // humidity ratio
) {
// FUNCTION INFORMATION:
// AUTHOR J. C. VanderZee
// DATE WRITTEN Feb. 1994
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P100, EQN 32
// by inverting function psyHFnTdbW
w = Math.max(w, 1e-5); // humidity ratio
var tdb = (h - 2.50094e6 * w) / (1.00484e3 + 1.85895e3 * w); // result=> dry-bulb temperature {C}
return tdb;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the Vapor Density in air as a
// function of dry bulb temperature, and Relative Humidity.
function psyRhovFnTdbRhLBnd0C(
tdb, // dry-bulb temperature {C}
rh // relative humidity value (0-1)
) {
// FUNCTION INFORMATION:
// AUTHOR R. J. Liesen
// DATE WRITTEN July 2000
// MODIFIED Name change to signify derivation and temperatures were used
// with 0C as minimum; LKL January 2008
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// Universal gas const for water vapor 461.52 J/(kg K)
// REFERENCES:
// ASHRAE handbook 1993 Fundamentals,
var rhoVaporDensity = rh / (461.52 * (tdb + KELVIN_CONV)) * Math.exp(23.7093 - 4111 / ((tdb + KELVIN_CONV) - 35.45)); // Vapor density in air
return rhoVaporDensity;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the Vapor Density in air as a
// function of dry bulb temperature, Humidity Ratio, and Barometric Pressure.
function psyRhovFnTdbWPb(
tdb, // dry-bulb temperature {C}
w, // humidity ratio
pb // Barometric Pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR R. J. Liesen
// DATE WRITTEN July 2000
// MODIFIED na
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// Universal gas const for water vapor 461.52 J/(kg K)
// REFERENCES:
// ASHRAE handbook 1993 Fundamentals,
w = Math.max(w, 1e-5); // humidity ratio
var rhoAir = w * pb / (461.52 * (tdb + KELVIN_CONV) * (w + 0.62198));
return rhoAir;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the Relative Humidity in air as a
// function of dry bulb temperature and Vapor Density.
function psyRhFnTdbRhovLBnd0C(
tdb, // dry-bulb temperature {C}
rhovapor // vapor density in air {kg/m3}
) {
// FUNCTION INFORMATION:
// AUTHOR R. J. Liesen
// DATE WRITTEN July 2000
// MODIFIED Name change to signify derivation and temperatures were used
// with 0C as minimum; LKL January 2008
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// Universal gas const for water vapor 461.52 J/(kg K)
// REFERENCES:
// ASHRAE handbook 1993 Fundamentals,
var rh = rhovapor > 0 ? rhovapor * 461.52 * (tdb + KELVIN_CONV) * Math.exp(-23.7093 + 4111 / ((tdb + KELVIN_CONV) - 35.45)) : 0;
if ((rh < 0) || (rh > 1)) {
rh = Math.min(Math.max(rh, 0.01), 1);
}
return rh;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the specific volume from dry-bulb temperature,
// humidity ratio and barometric pressure.
function psyVFnTdbWPb(
tdb, // dry-bulb temperature {C}
w, // humidity ratio
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P99, EQN 28
w = Math.max(w, 1e-5); // humidity ratio
var v = 1.59473e2 * (1 + 1.6078 * w) * (1.8 * tdb + 492) / pb; // specific volume {m3/kg}
return v;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the humidity ratio from dry-bulb temperature
// and enthalpy.
function psyWFnTdbH(
tdb, // dry-bulb temperature {C}
h // enthalpy {J/kg}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P100, EQN 32
var w = (h - 1.00484e3 * tdb) / (2.50094e6 + 1.85895e3 * tdb); // humidity ratio
// Validity test
if (w < 0) {
w = 1e-5;
}
return w;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the Vapor Density in air as a
// function of dry bulb temperature, and Relative Humidity.
function psyRhovFnTdbRh(
tdb, // dry-bulb temperature {C}
rh // relative humidity value (0-1)
) {
// FUNCTION INFORMATION:
// AUTHOR R. J. Liesen
// DATE WRITTEN July 2000
// MODIFIED Change temperature range applied (determine pws); Aug 2007; LKL
// Function is continuous over temperature spectrum
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// Universal gas const for water vapor 461.52 J/(kg K)
// REFERENCES:
// ASHRAE handbook 1993 Fundamentals, ??
// Used values from Table 2, HOF 2005, Chapter 6, to verify that these values match (at saturation)
// values from psyRhFnTdbWPb
var rhovapordensity = (psyPsatFnTemp(tdb) * rh) / (461.52 * (tdb + KELVIN_CONV)); // Vapor density in air
return rhovapordensity;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the Relative Humidity in air as a
// function of dry bulb temperature and Vapor Density.
function psyRhFnTdbRhov(
tdb, // dry-bulb temperature {C}
rhovapor // vapor density in air {kg/m3}
) {
// FUNCTION INFORMATION:
// AUTHOR R. J. Liesen
// DATE WRITTEN July 2000
// MODIFIED Change temperature range applied (determine pws); Aug 2007; LKL
// Function is continuous over temperature spectrum
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// ideal gas law
// Universal gas const for water vapor 461.52 J/(kg K)
// REFERENCES:
// ASHRAE handbook 1993 Fundamentals,
// Used values from Table 2, HOF 2005, Chapter 6, to verify that these values match (at saturation)
// values from psyRhFnTdbWPb
// FUNCTION PARAMETER DEFINITIONS:
var rh = rhovapor > 0 ? rhovapor * 461.52 * (tdb + KELVIN_CONV) / psyPsatFnTemp(tdb) : 0.0;
if ((rh < 0) || (rh > 1)) {
rh = Math.min(Math.max(rh, 0.01), 1);
}
return rh;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the relative humidity value (0-1) as a result of
// dry-bulb temperature, humidity ratio and barometric pressure.
function psyRhFnTdbWPb(
tdb, // dry-bulb temperature {C}
w, // humidity ratio
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR Richard J. Liesen
// DATE WRITTEN Nov 1988
// MODIFIED Aug 1989, Michael J. Witte
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK FUNDAMENTALS 1985, P6.12, EQN 10,21,23
// FUNCTION PARAMETER DEFINITIONS:
var pws = psyPsatFnTemp(tdb); // Pressure -- saturated for pure water
// Find Degree Of Saturation
w = Math.max(w, 1e-5); // humidity ratio
var u = w / (0.62198 * pws / (pb - pws)); // Degree of Saturation
// Calculate The Relative Humidity
var rh = u / (1 - (1 - u) * (pws / pb));
// Validity test
if ((rh < 0) || (rh > 1)) {
rh = Math.min(Math.max(rh, 0.01), 1);
}
return rh;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the humidity ratio from dew-point temperature
// and barometric pressure.
function psyWFnTdpPb(
tdp, // dew-point temperature {C}
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P99, EQN 22
// FUNCTION PARAMETER DEFINITIONS:
var pdew = psyPsatFnTemp(tdp); // saturation pressure at dew-point temperature {Pascals}
var w = pdew * 0.62198 / (pb - pdew); // humidity ratio
// Validity test
if (w < 0) {
w = 1e-5;
}
return w;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the humidity ratio from dry-bulb temperature,
// relative humidty (value) and barometric pressure.
function psyWFnTdbRhPb(
tdb, // dry-bulb temperature {C}
rh, // relative humidity value (0-1)
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P99, EQN 22
// FUNCTION PARAMETER DEFINITIONS:
var pdew = rh * psyPsatFnTemp(tdb); // Pressure at dew-point temperature {Pascals}
// Numeric error check when the temperature and rh values cause Pdew to equal or exceed
// barometric pressure which is physically impossible. An approach limit of 1000 pascals
// was chosen to keep the numerics stable as the denominator approaches 0.
// THIS EQUATION IN SI UNIT IS FROM ASHRAE HANDBOOK OF FUNDAMENTALS PAGE 99 EQUATION 22
var w = pdew * 0.62198 / Math.max(pb - pdew, 1000); // humidity ratio
// Validity test
if (w < 0) {
w = 1e-5;
}
return w;
}
// PURPOSE OF THIS FUNCTION:
// This function provides the humidity ratio from dry-bulb temperature,
// wet-bulb temperature and barometric pressure.
function psyWFnTdbTwbPb(
tdb, // dry-bulb temperature {C}
twb, // wet-bulb temperature {C}
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P99, EQ 22,35
// FUNCTION PARAMETER DEFINITIONS:
// Validity check
if (twb > tdb) {
twb = tdb;
}
// Calculation
var pwet = psyPsatFnTemp(twb); // Pressure at wet-bulb temperature {Pascals}
var wwb = 0.62198 * pwet / (pb - pwet); // Humidity ratio at wet-bulb temperature
var w = ((2501 - 2.381 * twb) * wwb - (tdb - twb)) / (2501 + 1.805 * tdb - 4.186 * twb); // humidity ratio
// Validity check
if (w < 0) {
w = psyWFnTdbRhPb(tdb, 0.0001, pb);
}
return w;
}
// PURPOSE OF THIS FUNCTION:
// This function provides air enthalpy from temperature and relative humidity.
function psyHFnTdbRhPb(
tdb, // dry-bulb temperature {C}
rh, // relative humidity value (0 - 1)
pb // barometric pressure (N/M**2) {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR J. C. VanderZee
// DATE WRITTEN Feb. 1994
// MODIFIED na
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P100, EQN 32
// by using functions psyWFnTdbRhPb and psyHFnTdbW
return psyHFnTdbW(tdb, Math.max(psyWFnTdbRhPb(tdb, rh, pb), 1e-5)); // enthalpy {J/kg}
}
// PURPOSE OF THIS FUNCTION:
// This function calculates the dew-point temperature {C} from humidity ratio and pressure.
function psyTdpFnWPb(
w, // humidity ratio
pb // barometric pressure (N/M**2) {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
// METHODOLOGY EMPLOYED:
// na
// REFERENCES:
// ASHRAE HANDBOOK OF FUNDAMENTALS, 1972, P.99, EQN 22
w = Math.max(w, 1e-5); // limited humidity ratio
var pdew = pb * W0 / (0.62198 + W0); // pressure at dew point temperature
var tsat = psyTsatFnPb(pdew);
return tsat;
}
// PURPOSE OF THIS FUNCTION:
// This function calculates the dew-point temperature {C} from dry-bulb, wet-bulb and pressure.
function psyTdpFnTdbTwbPb(
tdb, // dry-bulb temperature {C}
twb, // wet-bulb temperature {C}
pb // barometric pressure (N/M**2) {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED na
var w = Math.max(psyWFnTdbTwbPb(tdb, twb, pb), 1e-5);
var tdp = psyTdpFnWPb(w, pb);
if (tdp > twb) {
tdp = twb;
}
return tdp;
}
function psyTsatFnPb(
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// RE-ENGINEERED Dec 2003; Rahul Chillar
// PURPOSE OF THIS FUNCTION:
// This function provides the saturation temperature from barometric pressure.
// METHODOLOGY EMPLOYED:
// na
// REFERENCES:
// 1989 ASHRAE Handbook - Fundamentals
// Checked against 2005 HOF, Chap 6, Table 3 (using pressure in, temperature out) with
// good correlation from -60C to 160C
var itmax = 50; // Maximum number of iterations
var convTol = 0.0001;
// FUNCTION LOCAL VARIABLE DECLARATIONS:
var pbSave = -99999;
var tSatSave = -99999;
var tSat; // Water temperature guess
var iter; // Iteration counter
// Check press in range.
if (pb == pbSave) {
return tSatSave;
}
pbSave = pb;
// Uses an iterative process to determine the saturation temperature at a given
// pressure by correlating saturated water vapor as a function of temperature.
// Initial guess of boiling temperature
tSat = 100;
iter = 0;
// If above 1555000,set value of Temp corresponding to Saturation Pressure of 1555000 Pascal.
if (pb >= 1555000) {
tSat = 200;
// If below 0.0017,set value of Temp corresponding to Saturation Pressure of 0.0017 Pascal.
} else if (pb <= 0.0017) {
tSat = -100;
// Setting Value of PsyTsatFnPb= 0C, due to non-continuous function for Saturation Pressure at 0C.
} else if ((pb > 611) && (pb < 611.25)) {
tSat = 0;
} else {
// Iterate to find the saturation temperature
// of water given the total pressure
// Set iteration loop parameters
// make sure these are initialized
var pSat; // Pressure corresponding to temp. guess
var error; // Deviation of dependent variable in iteration
var x1; // Previous value of independent variable in ITERATE
var y1; // Previous value of dependent variable in ITERATE
var resultx; // resultx is the final Iteration result passed back to the calling routine
var icvg; // Iteration convergence flag
for (iter = 1; iter <= itmax; ++iter) {
// Calculate saturation pressure for estimated boiling temperature
pSat = psyPsatFnTemp(tSat);
// Compare with specified pressure and update estimate of temperature
error = pb - pSat;
//Iterate( ResultX, convTol, tSat, error, X1, Y1, iter, icvg );
var small = 1e-9;
var perturb = 0.1;
// Check for convergence by comparing change in X
if (iter != 1 && (Math.abs(tSat - x1) < convTol || error === 0)) {
resultx = tSat;
icvg = 1;
} else {
// Not converged
icvg = 0;
if (iter === 1) {
// New guess is specified by Perturb
if (Math.abs(tSat) > small) {
resultx = tSat * (1 + perturb);
} else {
resultx = perturb;
}
} else {
// New guess calculated from LINEAR FIT of most recent two points
var dy = error - y1;
if (Math.abs(dy) < small) dy = small;
// new estimation
resultx = (error * x1 - y1 * tSat) / dy;
}
x1 = tSat;
y1 = error;
}
tSat = resultx;
// If converged leave loop iteration
if (icvg == 1) break;
// Water temperature not converged, repeat calculations with new
// estimate of water temperature
}
// Saturation temperature has not converged after maximum specified
// iterations. Print error message, set return error flag, and RETURN
} // End If for the Pressure Range Checking
// Result is SatTemperature
return tSat; // result=> saturation temperature {C}
}
// PURPOSE OF THIS FUNCTION:
// This function provides the wet-bulb temperature from dry-bulb temperature,
// humidity ratio and barometric pressure.
function psyTwbFnTdbWPb(
tdb, // dry-bulb temperature {C}
w, // humidity ratio
pb // barometric pressure {Pascals}
) {
// FUNCTION INFORMATION:
// AUTHOR George Shih
// DATE WRITTEN May 1976
// MODIFIED na
// RE-ENGINEERED Dec 2003; Rahul Chillar
// 2011; as time saving measure, cache some values.
// METHODOLOGY EMPLOYED:
// Uses an Iterative procedure to calculate WetBulbTemperature
// Return value
var twb; // result=> Temperature Wet-Bulb {C}
// Locals
// FUNCTION ARGUMENT DEFINITIONS:
// FUNCTION PARAMETER DEFINITIONS:
var itmax = 100; // Maximum No of Iterations
var convTol = 0.0001;
// FUNCTION LOCAL VARIABLE DECLARATIONS:
var tBoil = 100; // Guess for boiling temperature of water at given pressure
var wnew; // Humidity ratio calculated with wet bulb guess
var w; // Humidity ratio entered and corrected as necessary
var resultx; // resultx is the final Iteration result passed back to the calling routine
var error; // Deviation of dependent variable in iteration
var x1; // Independent variable in ITERATE
var y1; // Dependent variable in ITERATE
var wstar; // Humidity ratio as a function of Sat Press of Wet Bulb
var psatstar; // Saturation pressure at wet bulb temperature
var iter; // Iteration counter
var icvg; // Iteration convergence flag
var FlagError; // set when errors should be flagged
// CHECK tdb IN RANGE.
if (tdb <= -100) {
console.warning("psyTwbFnTdbWPb - Dry bulb temperature was below -100C, assuming -100C");
tdb = -100;
}
if (tdb >= 200) {
console.warning("psyTwbFnTdbWPb - Dry bulb temperature was above 200C, assuming 200C");
tdb = 200;
}
// CHECK w IN RANGE.
if (w < 0) {
w = 1e-5;
}
// Initial temperature guess at atmospheric pressure
tBoil = psyTsatFnPb(pb);
// Set initial guess of WetBulbTemp=Entering Dry Bulb Temperature
twb = tdb;
// Begin iteration loop
for (iter = 1; iter <= itmax; iter++) {
// Assigning a value to twb
if (twb >= (tBoil - 0.09)) {
twb = tBoil - 0.1;
}
// Determine the saturation pressure for wet bulb temperature
psatstar = psyPsatFnTemp(twb);
// Determine humidity ratio for given saturation pressure
wstar = 0.62198 * psatstar / (pb - psatstar);
// Calculate new humidity ratio and determine difference from known
// humidity ratio which is wStar calculated earlier
wnew = ((2501 - 2.381 * twb) * wstar - (tdb - twb)) / (2501 + 1.805 * tdb - 4.186 * twb);
// Check error, if not satisfied, calculate new guess and iterate
error = w - wnew;
// Using Iterative Procedure to Calculate WetBulb
//Iterate( resultx, convTol, twb, error, x1, y1, iter, icvg );
var small = 1e-9;
var perturb = 0.1;
// Check for convergence by comparing change in X
if (iter != 1 && (Math.abs(twb - x1) < convTol || error === 0)) {
resultx = twb;
icvg = 1;
} else {
// Not converged
icvg = 0;
if (iter === 1) {
// New guess is specified by Perturb
if (Math.abs(twb) > small) {
resultx = twb * (1 + perturb);
} else {
resultx = perturb;
}
} else {
// New guess calculated from LINEAR FIT of most recent two points
var dy = error - y1;
if (Math.abs(dy) < small) dy = small;
// new estimation
resultx = (error * x1 - y1 * twb) / dy;
}
x1 = twb;
y1 = error;
}
twb = resultx;
// If converged, leave iteration loop.
if (icvg === 1) break;
// Error Trap for the Discontinuous nature of PsyPsatFnTemp function (Sat Press Curve) at ~0 Deg C.
if ((psatstar > 611) && (psatstar < 611.25) && (Math.abs(error) <= 0.0001) && (iter > 4)) break;
} // End of Iteration Loop
// Wet bulb temperature has not converged after maximum specified
// iterations. Print error message, set return error flag, and RETURN
if (iter > itmax) {
//ShowRecurringWarningErrorAtEnd( "WetBulb not converged after max iterations(PsyTwbFnTdbWPb)", iPsyErrIndex( iPsyTwbFnTdbWPb3 ) );
}
// If (TempWetBulb)>(Dry Bulb Temp) , Setting (TempWetBulb)=(DryBulbTemp).
if (twb > tdb) {
twb = tdb;
}
return twb;
}
</script>
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