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<!DOCTYPE html>
<html lang="en">
<head>
<title>RTU Bin-Method Calculator - Help</title>
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<a name="Intro"></a>
<h1 class="maintitle">Bin-Method Calculator — Help</h1>
<p>This help is a collection of topics for the features on the calculator's
<em>Controls</em> page. These help topics can be accessed by clicking on the
information icon next to a feature's name. This opens the help window and
positions the corresponding topic at the top.
</p>
<p>Help topics are outlined as follows: </p>
<blockquote>
<p><strong>Name: </strong>Following the feature's
name is summary content that is similar to the pop-up tip that
is viewed by positioning the mouse cursor over an
information icon (and waiting a second or so). </p>
<p><strong>Discussion: </strong>General tips on usage will be first in the
discussion section. Following this may be qualitative discussions of
expected behaviors when changing the values of this feature.</p>
</blockquote>
<hr>
<p><a name="WebBrowser" id="WebBrowser"></a><strong>Web Browsers:</strong>
The calculator is tested and fully functional in Mozilla Firefox,
Microsoft Edge, Apple Safari, and Google Chrome. Performance
and display characteristics are best in Firefox. Starting with calculator
version 4.3, WebKit-based browsers such as Google Chrome are supported.</p>
<hr>
<p><a name="SavingRuns" id="SavingRuns"></a><strong>Submitting the
<em>Controls</em> page (and saving the <em>Results</em> page):</strong> Click
one of the "Submit" buttons or any of the gray divider rows to submit the
<em>Controls</em> page to the calculation engine.</p>
<p>The
<em>Controls</em> and <em>Results</em> pages can
be saved as local web pages to record run parameters and
performance results. Note that a parameter-summary table is
included on
the <em>Results</em> page (after the "Results" table and chart).
</p>
<p><strong>Discussion: </strong>To capture the details of a calculator run, do a
"save-page-as" from the browser and then pick the "web-page, complete" option.
This works well from the Firefox and Google Chrome browsers. Google Chrome
does the best job capturing all formatting details. Tables, images (graphs),
and everything will be captured. (Note that currently the MS Internet Explorer
browser does not properly capture the <em>Results</em> page.) From the saved
local page, or directly from the original page, you can drag your cursor over
tables and paste them into Excel for additional analysis.</p>
<p>The <em>Controls</em> and <em>Results</em> pages can also be printed to multiple
sheets of letter size paper. Print from the "File / Print" menu
option
and not the "File / Print preview" option.</p>
<hr>
<a name="Defaults" id="Defaults"></a><strong>Defaults:</strong>
Use the "Restore" button to change all feature values back to the defaults
shown in the far right column. If a feature has been
changed
from its default value, the background color of the corresponding
cell
in this column changes to a slightly darker shade. This color change
is intended as an additional reminder to the user as to which
features
are actively being changed.
<p>Most of the default values are static. However, some defaults are
calculated (and updated) depending on the settings of other features.
"Ventilation Rate" and the three "Power Inputs" features are examples of
defaults that depend on other features.</p>
<p>The "Power" button is displayed next to the "Restore" button if the
"Advanced Features" are turned on. The "Power" button acts to reset the power
draw values. Clicking the "Power" button will cause the three power fields
(evaporator, auxiliary, and condenser) to be set to default levels as
calculated based on current settings of the "EER" and "Capacity" features.
(See additional discussion in the help topic for the <a class="Jump" href="#FanCondAux">Power Inputs</a>
feature.)</p>
<hr>
<p><a name="Advanced_controls" id="Advanced_controls"></a><strong>Advanced features:</strong>
Unhide advanced calculator features and initialize them to their default values.</p>
<p>Advanced features are indicated by a tan background color in the features title cell. </p>
<p><strong>Discussion:</strong>
Advanced features were new with the second release of the calculator. The
new features in that release and those after are listed in the calculator's <a
class="Jump" href="RevisionHistory.html">revision history</a>.</p>
<hr>
<p> <a name="Building_Type" id="Building_Type"></a><strong>Building
Type: </strong>Select the building type which best represents
your building. Each building type has an associated load model
that is
used to predict RTU loads and mechanical ventilation as a function
of
outdoor temperature. Each load model is derived from EnergyPlus
analysis on a prototype ASHRAE building.</p>
<p>"Ventilation Rate" is calculated as the
building type is changed. Manually entered values for "Ventilation Rate" will be
overwritten whenever the building-type
selection is changed. </p>
<p>To input custom load-model parameters, select the "Advanced
Features" option, then edit the parameter fields below the "Building
Type" feature.
Refer to the help section on <a class="Jump" href="#Custom_Load_Model">custom
load models</a>. </p>
<p>If the load-line is <a class="Jump" href="#Lock_load_line">locked</a>, the
building type (and two of the parameters in the custom-load model) will be
locked (disabled). When locked, ventilation levels can be changed directly or
by the ventilation parameter in the custom model.</p>
<p><strong>Discussion:</strong> There are two supporting PDF documents that
can be downloaded: (1) the description of the <a class="Jump" target="_blank"
href="docs/prototype%20buildings%20HVAC%20summaries.pdf">prototype
buildings</a>, see pages 8-13, and (2) a description of the corresponding
EnergyPlus analysis done to develop the load models (see Appendix A in the <a
href="docs/PNNL-24130.pdf" class="Jump" target="_blank">User
Manual</a>).</p>
<hr>
<a name="Custom_Load_Model" id="Building_Type"></a><strong>Custom
Load Model:</strong> To define a custom load model, edit the
three parameters and
then click the "Apply" button. This calculates new values for
associated
features and must be done before submitting the form. (The
"Advanced Features" option must be selected to show
the parameter fields for the custom load model.)<span style="font-weight: bold;"><br>
<br>
</span>The parameter
values for the custom model are initialized to the
default parameters for the currently-selected building type.<br>
<br>
When
entering custom load-model parameters, the units are KBtu/HrF for
the slope (S), KBtu/Hr for the intercept (I), and dimensionless for
the
ventilation-slope fraction (VSF). After editing these custom
parameters, the "Apply" button must be used to calculate the
corresponding
new values for the "Ventilation Rate"
parameter.<br>
<p>If
the load-line is <a class="Jump" href="#Lock_load_line">locked</a>,
two of
the parameters of the custom-load model are locked (disabled) and
cannot be changed. If locked, ventilation levels can be
changed
directly with the "Ventilation Rate" feature or with the ventilation
parameter
in the custom load model. The "Apply" button applies the
ventilation
levels set in the load model and overwrites any changes manually
entered through the "Ventilation Rate" feature.</p>
<span style="font-weight: bold;">Discussion:</span>
A custom load model
is defined to describe the approximate linear
relationship between the sensible-cooling load on the HVAC
system and
the difference between the
inside and outdoor temperatures. The model is characterized by three
parameters: (1) a slope parameter accounting for conduction,
ventilation, and infiltration through the building envelope, (2) an
intercept parameter accounting for internal loads, and (3) a
ventilation-slope fraction parameter that specifies how much of the
first parameter is caused by ventilation. Refer to the help section
on <a class="Jump" href="#Building_Type">building
types</a> for additional information. Appendix A in the <a href="docs/PNNL-24130.pdf"
class="Jump" target="_blank">User
Manual</a>
PDF further describes the concepts and analysis behind this
approach.<br>
<br>
The
slope and intercept of the load model are scaled to produce a
sensible
load that is in balance with the sensible capacity of the RTU at
design
conditions. In a sense, the building is scaled (sized) to match the
capacity of the cooling system. This scaling operation produces the
final load-line that is
processed in the binned analysis.<br>
<hr>
<p><a name="State"></a><strong>State/City:
</strong>The "State" feature affects the lists of cities appearing
in the "City" feature. The "State" and "City" features are used
together to
query weather data for this location. If your city is not listed,
select the city whose climate is most similar yours (usually the
closest city).</p>
<p>
<strong>Discussion:</strong> The calculator uses
weather data
to conduct a binned energy analysis for the RTU in cities across
the
United
States. Weather tape data (outdoor dry-bulb and coincident
web-bulb)
was
binned in 5 degree increments and filtered by the selected
occupancy <a class="Jump" href="#Schedule">schedule</a>. The
result is a database of hours (in each bin) and coincident
wet-bulb
temperatures for each city and schedule combination.
</p>
<hr>
<p><a name="Schedule"></a><strong>Schedule:
</strong>This defines the time during which the building is assumed to be
occupied. For the unoccupied periods outside of this schedule, the air
conditioner is assumed to be shut down (no runtime) or the thermostat is set
back. The system behavior during unoccupied periods is determined by the
“Indoor Temperature” and the “E-Fan and Condenser” features.</p>
<p><strong>Discussion:</strong> The "Schedule" feature
filters the number of hours that can accumulate in a weather bin.
Shorter
occupant schedules translate into fewer potential hours where the
cooling system can be subject to a load.</p>
<p>The hours outside
of this schedule are considered to be unoccupied if the "Indoor
Temperature" feature is set to "Cond. Off."</p>
<hr>
<p><a name="Indoor_Temperature"></a><strong>Indoor
Temperature: </strong>
This is the thermostat setpoint. The second feature, "Setback,"
acts to
increase the cooling setpoint temperature during unoccupied hours.
The
cooling setpoint, during unoccupied hours, is calculated as the
sum of
these two features (base setpoint + setback = higher setpoint
during
the unoccupied hours). Additional information for this feature can
be
found in the topic for the <a class="Jump" href="#FanControls">E-Fan and Condenser</a> feature.</p>
<p>This "Setback" feature acts to perform a double run. The
load-line is established (locked) in the primary run (for occupied
hours) at non-setback conditions. The same load-line is applied
again
in the secondary setback run for the unoccupied hours. The sum of
the
two runs is used to populate the energy categories in the
"Results"
table.</p>
<p>A special case is considered when "Setback" is set to "Cond.
Off."
In this case the
condenser and the evaporator fan are not allowed to run during
unoccupied hours and during
these unoccupied hours only auxiliary energy is
calculated (and totaled). In this case bin calculations are not
displayed for the
unoccupied hours.<br>
</p>
<p>For all normal setback cases, both condenser and fan energy
(and aux energy) are calculated during unoccupied hours. Turning
on the
"Show Bin Calculations" option will display separate bin
calculations
for these unoccupied hours. This is in addition to (displayed
after)
the occupied-hours bin calculations. (Note: there will be a link
above
each of the two "Loads and Hours" plots for
the candidate unit. Clicking this link will scroll/jump the page
back
and forth between the occupied and the unoccupied-hours results.
Just
clicking this twice will put this jump into the browser's page
history
and then you can use the Alt-arrow keys (hold Alt key down, then
try
the left and right arrow keys) to toggle back and forth. This can
be
a useful trick for visually comparing the occupied and unoccupied
results.)</p>
<p>Note that for staged systems using normal setback, the
evaporator
fan will cycle with the compressor
during the unoccupied hours. However if the special case of "Cond.
Off"
is selected, the condenser and the evaporator fan are always off
during
unoccupied hours.</p>
<p>The "Schedule" (Scheduled Hours) trace is shown in
the "Loads and Hours" chart. This illustrates the occupied hours
where
the condenser is allowed to operate as established by the selected
schedule. The "Total Hrs" trace shows all the hours (sum of
occupied
and unoccupied). Note that for normal setback, the
"Schedule" trace in the "Loads and Hours" chart for
unoccupied
hours
will represent the unoccupied hours (i.e. the hours where the
condenser is active in the setback run for the unoccupied times).</p>
<p><strong>Discussion:</strong> When interpreting the
impact of changes to the thermostat "Indoor Temperature" setpoint feature,
consideration
must be given to whether the non-ventilation load-line is locked
or
not. If the load-line is locked, this feature will give the most
intuitive results. However, in the default state (load-line
un-locked),
the impact of this feature may be less than expected. Consider the
following example:</p>
<table width="394">
<thead>
<tr>
<th width="175">Indoor Temperature </th>
<th width="207">Candidate Unit (kWhrs) </th>
</tr>
</thead>
<tbody>
<tr>
<td> 75 </td>
<td>10,798 </td>
</tr>
<tr>
<td> 70 </td>
<td>12,807</td>
</tr>
<tr>
<td> 70L (line locked @ 75) </td>
<td>14,670</td>
</tr>
</tbody>
<tfoot>
<tr>
<td colspan="2"> Note: All other calculator parameters are at
default values. </td>
</tr>
</tfoot>
</table>
<p>For the <em>locked</em> case (third row in table
above), the primary
driver behind the larger increase is that the non-ventilation
load-line
is not
automatically adjusting to accommodate the more severe conditions
at
the lower
setpoint (see discussion on the <a class="Jump" href="#Lock_load_line">locking</a> feature). So the
effect of the original non-ventilation load-line (based on
delta-T) is
clearly increased by the lower setpoint.</p>
<p>In the contrasting <em>un-locked</em> case
(second row), the load-line
is defined to be in balance with the capacity (see <a class="Jump" href="methods/NonVentilationLoad.html">methods
page</a>). So the change in setpoint has a less direct impact on
the
consumption. This is because the lower return temperatures
adversely
affect mixed-air conditions and the corresponding system
performance.
And
to achieve balance between total sensible load and the reduced
capacity, the
total sensible load must be reduced. Therefore, the primary driver
behind
the increase in consumption, for this case, is not directly loads,
but
rather
seen most strongly in two associated effects:</p>
<blockquote>
<ol>
<li><em>Mixed-air conditions</em>: The lower
return temperature affects the load-line calculation (at
design), the
capacity (at bin conditions), and the power (at bin
conditions) used
while satisfying the load. The overall effect is an increase
in power
usage (see similar discussion of the un-locked case for the
"Ventilation
Rate" feature) </li>
<li><em>More cooling bins</em>: The lower
setpoint essentially extends the cooling season. There are
more bins
where the cooling loads are satisfied by the economizer but
still add
to energy consumption because of fan power. </li>
</ol>
</blockquote>
<p>Note that the setpoint affects the mixed-air
conditions (for both locked and un-locked cases). The lower return
temperature adversely affects the sensible capacity which
dominates
the performance-correction effects (see the bin data
for the
overall correction
factor (OCF)). The OCF factor is higher for the lower setpoint
cases.
Higher OCF factors
correspond to higher consumption.</p>
<hr>
<p><a name="Indoor_Relative_Humidity"></a><strong>Indoor
Relative Humidity: </strong>Uncheck the "auto" feature to
specify a fixed humidity level.
In "auto" mode the inside humidity reflects outdoor
conditions. In "fixed" mode, the indoor relative humidity is
assumed to
be
controlled to a fixed value.</p>
<p>
<strong>Discussion:</strong> The "auto" mode models
the interior humidity as <em>tracking</em> the outdoor conditions.
Tracking is equivalent to assuming a moisture mass balance if moisture
gains (from people and processes) equal moisture losses from condensate.
This approximation is a simple way to model humidity conditions if no
other information is known about moisture dynamics in the building. The
tracking mode calculates the interior relative humidity and wet-bulb by
assuming the moisture content of the interior air is equivalent to that of
the exterior air on a humidity ratio basis (i.e., mass of water per mass
of dry air is equivalent inside and out). The tracking mode is constrained
to allow indoor humidity of values no less than 20% and no more that 65%.
(The "auto" mode generally overestimates the interior humidity ratio. This
assumption tends to overestimate associated latent loads. There is a
discussion of this assumption in Section A.7 of the
<a class="Jump" href="docs/PNNL-24130.pdf" target="_blank">User Manual</a>.)<br>
<br>
Alternatively a "fixed" mode is used if the "auto" feature is
de-selected. In "fixed" mode, the interior humidity ratio is
assumed
fixed (at the user selected level) and is not affected by the
outside
conditions.<br>
<br>
If you know the typical humidity levels in your building during
the
summer, use the "fixed" mode (especially if you have an associated
piece of equipment that controls the humidity). If not, use the
"auto"
mode. Note that the calculator does not determine
the
energy usage of any associated humidification or dehumidification
devices. It strictly calculates energy estimates for the air
conditioner.<br>
<br>
The following reference discusses empirical validation of
simplified
methods for modeling humidity: Miller, J.D., "Development and
Validation of a Moisture Mass Balance Model for Predicting
Residential
Cooling Energy Consumption," ASHRAE Transactions, Vol. 90, pt. 2,
1984,
(275-293).<br>
<br>
Note that a <a class="Jump" href="methods/EquipmentResponse_Latent.html">sensible load analysis</a> best
represents a thermostat's sensible nature and is key in supporting the
calculations that are affected by humidity and latent loads. A
sensible thermostat responds to temperature changes and sends requests to
the unit to remove the sensible cooling load. The effects of humidity are
accounted for in how the unit's sensible capacity is diminished by humidity
in the entering air (mixture of outside and return).<br>
<br>
The change to a sensible analysis (in revision 2.0), from the
original
total-energy analysis, changes the question the
calculation answers from:<br>
<u><br>
Total energy question<br>
</u>Given the unit's total capacity at the specified entering
conditions, AND assuming that all sensible and latent loads are
met by
the unit,
how much energy would it consume in satisfying the total load?<br>
<br>
To this one:<u><br>
<br>
Sensible energy question</u><br>
Given the unit's available sensible capacity at the specified
entering
conditions, AND that the unit is controlled by a thermostat (a
purely
sensible device), how much energy would it consume in satisfying
the
sensible component of the total
load?
<!-- <hr /> <p><a name="Solar_and_Internal_Gains"></a><strong>Solar and Internal Gains: </strong> Specified as fraction of sensible capacity at design conditions. </p> <p>The S&I fraction is considered primarily a calculated value as affected by the building type and city selection. Manual changes to this factor are allowed but not recommended in version 4.1 of the RTUCC. Manual changes support comparisons with version 4.0 of the RTUCC.<span style="font-weight: bold;"> Instead, please use the editable fields associated with the "Building Type" control to establish a custom load line.</span> Also note that manual changes to the S&I factor persist only until this form is updated. An update will cause a calculated value to replace the manual entry.</p> <p><strong>Discussion: </strong>The <em>Solar and Internal Gains</em> control allows for qualitative characterization of the buildings sensitivity to internal cooling loads (all loads not driven by outside temperature). The S&I loads include all cooling loads except ventilation and conduction. This includes loads such as occupancy related internal loads (waste heat from lighting and plug loads) and also solar loads. These internal loads are assumed to be independent of outside conditions and constant through out the day.<br /> <br /> Increasing the S&I fraction results in a less steep load line (less sensitive to outside temperature) and decreasing the S&I fraction makes for a steeper load line (more sensitivity to outside temperature). Setting the S&I load fraction to zero is equivalent to modeling a building with no internal gains or windows (e.g., air conditioned storage building). With "Show bin calculations" selected, notice that increasing the S&I factor essentially lengthens the cooling season (more cooling bins are proceeded).<br /> <br /> Note that the S&I control has no effect if the non-ventilation load line is <a class="Jump" href="#Lock_load_line">locked</a>. </p> -->
</p>
<hr>
<p><a name="Total_Capacity"></a><strong>Total
Capacity: </strong>Select
the AHRI net cooling capacity of the equipment being used (or
equivalently, the
cooling load of the building).
</p>
<p>If a variable-speed system is selected using the "E-Fan and
Condenser" feature, the "Number of Stages" feature is ignored. In this case
all
the bin calculations are reported in the first stage.</p>
<p>
<strong>Discussion:</strong> This is the total (sensible
and
latent) net (including evaporator fan energy) cooling capacity at
AHRI
test conditions. <br>
<br>
In all cases (unless the <a class="Jump" href="#SpreadsheetData">spreadsheet
interface</a> is
used), the units are represented with this AHRI rated capacity,
the
EER,
and DOE-2 <a class="Jump" href="methods/CoolingCorrectionCurves.html">correction factors</a>.
</p>
<p>Note that changing the capacity value automatically changes
the default power values for the blower fan and the condenser.</p>
<hr>
<p><a name="N_stages"></a><strong>Number
of Stages: </strong>The number of stages (capacity levels) in
the RTU.
</p>
<p>This feature determines
whether the unit will process the load with one or multiple
stages. A
multiple-stage
system minimizes part-load cycling losses and evaporator-fan
energy
(see methods page on <a class="Jump" href="methods/EquipmentResponse.html">equipment
response to loads</a>).</p>
<p>
<strong>Discussion:</strong>
</p>
<p>If a variable-speed system is selected using the "E-Fan and
Condenser" feature, the "Number of Stages" feature is ignored.</p>
<p>A 2-stage
unit with a single-speed fan can be modeled by setting the "Number
of
Stages" feature to "2" and the "E-Fan and Condenser" feature
to
either of the "1-Spd" options.</p>
<p>Capacity levels for each "Number of Stages" setting are set as
follows:</p>
<table style="text-align: left; width: 349px; height: 80px;" border="1" cellpadding="2" cellspacing="2">
<tbody>
<tr>
<th style="background-color: white;">Stages</th>
<th style="background-color: white;">Capacity Levels</th>
</tr>
<tr>
<td>1</td>
<td class="left">1.0</td>
</tr>
<tr>
<td>2</td>
<td class="left">0.5, 1.0</td>
</tr>
<tr>
<td>3</td>
<td class="left">0.4, 0.6, 1.0</td>
</tr>
<tr>
<td>5</td>
<td class="left">0.2, 0.4, 0.6, 0.8, 1.0</td>
</tr>
<tr>
<td>10</td>
<td class="left">0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,
0.8, 0.9, 1.0</td>
</tr>
</tbody>
</table>
<p></p>
<hr>
<p><a name="Oversizing_Factor"></a><strong>Oversizing
Factor: </strong>
Percent that capacity exceeds load at design conditions.</p>
<p>
<strong>Discussion:</strong> This factor serves to diminish
the load so that the unit is effectively oversized at design
conditions.
</p>
<p>Blower-fan savings associated with variable-speed systems (see
"E-Fan and Condenser" feature) are larger for oversized units.</p>
<hr>
<p><a name="StoT_Ratio"></a><strong>S/T
Ratio: </strong>
Ratio of sensible to total capacity at AHRI test conditions.</p>
<p>
<strong>Discussion:</strong> The S/T ratio (@ AHRI
conditions)
is used in estimating the sensible capacity of the unit. This
along
with
the rated total capacity of the unit are the starting point for
calculating
sensible capacity and system power draw at conditions other than
AHRI
test
conditions. See the methods page on <a class="Jump" href="methods/CoolingCorrectionCurvesSensible.html">sensible
capacity</a> and also the page that calculates a table of <a class="Jump" href="bypass.asp">steady-state
system performance values</a> at conditions other than AHRI test
conditions.
</p>
<hr>
<p><a name="Candidate_Unit"></a><strong>Candidate
Unit: </strong>Energy Efficiency Ratio (EER), Cost (in k$), and
Maintenance Cost (in $) for the candidate unit.</p>
<p>Note that resetting the EER automatically changes the default
power values for the condenser.</p>
<p><strong>Discussion:</strong> </p>
<ul>
<li> EER: Net Capacity / Total System Power, as determined at
AHRI test conditions.</li>
<li>Cost: Total system purchase and installation cost (in units
of thousands of dollars).</li>
<li>Maintenance Cost: Total system annual maintenance costs (in
units of dollars).</li>
</ul>
<p>Note that IEER (Integrated Energy Efficiency Ratio) values are
not to be entered here. IEER values
are a demographically and operationally weighted average of a set
of
four representative part-load EER values. An IEER projects a
unit's
performance to a national level. These weighted averages are
intended
to rank units on a national basis. While IEER values are very
useful in
sorting units nationally, they are not intended for evaluating a
unit
for a particular climate and operation strategy. However, the raw
EER
part-load data that goes into the IEER calculation can be very
useful
for characterizing a unit's performance under specific conditions.</p>
<p>(Refer also to the help section on the <a class="Jump" href="#SpreadsheetData">spreadsheet interface</a>. The
modeling of the full and part-load data is described there.)</p>
<p>The spreadsheet interface serves to adapt this supporting EER
data (originally intended for the IEER calculations) for use in
modeling work: </p>
<ol>
<li><strong>A superset of the four points:</strong>
The four points are expanded to a table of sixteen. These added
points
give sufficient data for regressing the data as a function of
part-load
fraction and outdoor dry-bulb.</li>
<li><strong>Separation of evaporator and condenser power
draws: </strong>Removing the evaporator fan power from the
EER
data set allows for independent modeling of the condenser unit
and the
evaporator fan.</li>
</ol>
<hr><a name="Specific_RTU"></a><strong style="font-weight: normal;"><span style="font-weight: bold;">Specific
Candidate Unit:</span>
Select from a list of three specific high-performance RTU systems.</strong>
<p>Each
of these three options corresponds to a commercially available
rooftop
unit or an add-on control system. The basic features are
summarized
below.</p>
<ol>
<li><span style="font-weight: bold;">Advanced
Controls</span>: This is a retrofit fan controller that
minimizes fan usage for any RTU which has a single-speed fan.</li>
<li><span style="font-weight: bold;">Three Stages</span>:
This is a high-performance RTU with three stages. Capacity
levels are
40, 60, and 100 percent. This unit uses a three-speed evaporator
fan.</li>
<li><span style="font-weight: bold;">Variable-Speed
Compressor</span>:
This is a high performance RTU which uses a combination of
staging,
variable-capacity condensers, and a variable-speed evaporator
fan. This
unit first uses its variable capacity to meets the lower loads;
at
higher loads the additional stages are used.</li>
</ol>
<p><strong>Discussion:</strong></p>
<p>The setting of the <a class="Jump" href="#Indoor_Temperature">Setback</a> and <a class="Jump"
href="#FanControls">E-Fan and Condenser</a>
calculator parameters significantly affects the assessment of the
<span style="font-weight: bold;">Advanced Control</span>
system. Please also refer to the help topics for these two
calculator
parameters.
</p>
<p><strong><span style="font-weight: normal;">The
following outline lists the fan levels set by the Advanced
Control
system. For two-stage RTUs, the first-stage cooling runs the
fan at</span><span style="font-weight: normal;"> 75% and
second-stage cooling
runs the fan at 90%. Single-stage RTUs address all calls for</span><span style="font-weight: normal;"> cooling
by running the fan at
90%.</span><br style="font-weight: normal;">
</strong></p>
<ul>
<li><strong><span style="font-weight: normal;">No
call for cooling:</span></strong></li>
<ul>
<li><strong><span style="font-weight: normal;">Fan
runs at 40%</span></strong></li>
</ul>
<li><strong><span style="font-weight: normal;">Normal
operation</span></strong></li>
<ul>
<li><strong><span style="font-weight: normal;">First-stage
call:</span></strong></li>
<ul>
<li>ODB >= 70F; <strong><span style="font-weight:
normal;">Fan at 75%</span></strong></li>
<li>ODB < 70F; <strong><span style="font-weight:
normal;">Fan at 90%</span></strong></li>
</ul>
<li><strong><span style="font-weight: normal;">Second-stage
call: Fan at 90%</span></strong></li>
</ul>
<li><strong><span style="font-weight: normal;">Economizer</span></strong></li>
<ul>
<li>Fan at 75%<strong><span style="font-weight: normal;"></span></strong></li>
<li><strong><span style="font-weight: normal;">Fan at
90% (integrated)</span></strong></li>
</ul>
</ul>
<p>Selection
of either the <span style="font-weight: bold;">Three
Stages </span>or the <span style="font-weight: bold;">Variable-Speed
Compressor</span> RTU options invokes corresponding sets of
capacity
and efficiency correction curves for that unit. The <span style="font-weight: bold;">"Advanced Controls"</span>
option only affects the behavior of the evaporator fan and
therefore
uses the default corrections curves.</p>
<p>Note that selection
of a specific unit acts to configure associated features for the
candidate unit. For example, selecting the "Three Stages" option
sets
the "Number of Stages" feature to "3" and the "E-Fan and
Condenser"
feature to "N-Spd: Always ON." Specific performance curves are
used in
the calculation engine depending on the selection.</p>
<p>However,
a selection here does not automatically set either the "EER,"
Total
Capacity," or "Power Inputs" fields. It is necessary for the user
to
set
these manually.</p>
<hr><a name="Standard_Unit"></a><strong>Standard
Unit: </strong>Energy Efficiency Ratio (EER), Cost (in k$), and
Maintenance Cost (in $) for the standard unit.
<p><strong>Discussion:</strong> See discussion under <a class="Jump" href="#Candidate_Unit">Candidate
unit</a> section.</p>
<p>
Note that the "Standard Unit" cost features can be used to
investigate
the economics of replacing an existing unit (with indefinite life
remaining). In this case, the standard unit is not new and
represents
an existing unit. For example, starting with default settings, set
the
standard (existing) unit to an EER of 8 and a cost of 1k$ (assumed
cost
for an anticipated compressor replacement). Adjust maintenance
costs to
reflect the need for more annual service on the existing unit.</p>
<hr>
<p><a name="FanCondAux"></a><strong>Power
Inputs: </strong>
Specification of all the power inputs at AHRI rating
conditions
(in kWatts). This includes the
evaporator fan (blower), auxiliary power (power needed for control
electronics), and condenser unit (fan and compressor).
</p>
<p>
These three fields are initialized to default levels based on the
total
capacity and EER of the unit. Changing these three values
will cause the EER to be recalculated. A helpful editing pattern
is to
first edit the "EFn" and "Aux" fields, then
re-enter the "EER" value. Clicking the "Power" button (top
or bottom right) will cause the three fields to be set
to default levels based on current EER and Capacity. Note that
blower
power can be determined from manufacturer's performance data as
the
difference between gross and net capacity when expressed in
kWatts.</p>
<p>(Note that condenser-fan power can be specified with
the <a class="Jump" href="#Condenser_Fan">Condenser
Fan</a>
feature.)</p>
<p>The corresponding three categories of energy consumption are
shown as columns in the bin-calcs table (the "Show Bin
Calculations"
option must be on). Their annual sums are shown in the "Results"
table
(the "Advanced Features" option must be on).</p>
<hr>
<p>
<strong><a name="Condenser_Fan"></a>Condenser
Fan:</strong>
Condenser-fan power as a percentage of the total condenser
power
(at AHRI rating conditions).<br>
</p>
<p>This feature has an effect on energy
calculations ONLY in the case of variable-capacity condensers.
This
feature is disabled if the "E-Fan and
Condenser" feature is set to a non-variable-speed mode.
</p>
<p><strong><span style="font-weight: bold;">Discussion</span></strong><span style="font-weight: bold;">:</span>
This feature acts to split out the condenser-fan power for use in
accounting for the reduced-power draw of variable-speed condenser
fans
in the calculation engine. It has impact ONLY in the case of
a
variable-speed system. Fan-affinity
laws are used to estimate the reduced (from full-load) power
consumption
of the condenser fan. Full-load condenser-fan power is calculated
as
this feature's indicated percentage of the AHRI-rated condenser
power
(as specified in the "Cnd" field of the <a class="Jump" href="#FanCondAux">Power
Inputs</a> section).</p>
<hr>
<strong></strong><a name="FanControls"></a><strong></strong><span style="font-weight: bold;">E-Fan and
Condenser</span><strong>:
</strong>Characteristics of the evaporator fan and the condenser.
<p>This feature is dual purpose in that it allows the user to
select:
(1) the fan type for single or multiple-stage systems or
(2) a variable-speed system (i.e. variable-capacity condenser
and a variable-speed evaporator fan).<br>
</p>
<p>The following options are available:<br>
</p>
<ul>
<li>1-Speed Fan (1-Spd) for 1 or 2-Stage Condenser: </li>
<ul>
<li>Always ON<comment title="OFF When Unoccupied (i.e., always
ON during schedule, otherwise OFF outside of schedule if
setback control is set to "Cond. Off")"></comment>
</li>
</ul>
<ul>
<li>Cycles With Compressor</li>
</ul>
<li>N-Speed Fan (N-Spd) for N-Stage Condenser: </li>
<ul>
<li>Always ON</li>
</ul>
<ul>
<li>Cycles With Compressor</li>
</ul>
<li>Variable-Speed Fan for Variable-Capacity Condenser
(V-Spd):</li>
<ul>
<li>Always ON</li>
</ul>
</ul>
<p>The "Cycles with Compressor" fan modes will cycle the blower
fan
with the compressor during both occupied and unoccupied hours. In
this
case the fan is completely off whenever the compressor is off. An
exception to this occurs when the economizer is active. When
economizing, the blower fan always runs at full speed.</p>
<p>The
“…Always ON” fan-mode choices for staged units will cause the
blower
fan to be “…Always ON” during occupied hours, but will cycle
the fan with the compressor during unoccupied hours. In other
words,
the "...Always ON" mode runs the fan at all times during occupied
hours, but cycles during unoccupied hours. The fan is
effectively in "Cycles With Compressor" mode during unoccupied
hours.</p>
<p>The behavior
of the system during unoccupied hours is affected by the
"Setback"
feature which determines if the condenser is allowed to run during
that
time. When the "Setback" feature is set
to "Cond. Off,"
then DX cooling and the evaporator fan are kept off during the
unoccupied hours. When
the "Setback" feature is set to any
value other than "Cond. Off," then DX cooling is allowed during
unoccupied hours and at loads as determined by a reduced
thermostat
setpoint.</p>
<p>A special case where the condenser and the evaporator
fan
are OFF during
unoccupied hours can be investigated by setting the "Setback"
feature to "Cond. Off." This will set everything OFF
during
unoccupied hours independent of how the "E-Fan and Condenser"
feature
is set.</p>
<p>(For clarity, the following two paragraphs restate the
information above from a different perspective: condenser ON or
OFF.)</p>
Blower-fan energy, when the
condenser is OFF, is handled in three ways: (1) If a “Cycles…” fan