myPLV Frequently Asked Questions

  • What is new in this release?

      This release provides:

       - Modified programming to improve performance associated with the Excel 2013 release

       - A new worksheet is added for exploring system performance when varying condenser water design flow rate (see the next 2 questions and the relevant section in the "Getting Started" tab)

  • What is IPLV and why is it not a good system energy use predictor?

      The Integrated Part Load Value (IPLV) is a performance metric developed by AHRI as a means by which chiller efficiency may be rated based on the weighted average of four load points, each at a prescribed condenser temperature.  According to AHRI 550/590 Appendix D, the IPLV value was not intended to be used to predict the annualized energy consumption of a chiller in any specific application or set of operating conditions.  This is because the operational points and respective weightings which make up the IPLV method do not represent an individual chiller plant design, location, or operation and therefore will not provide reliable data to estimate chiller energy consumption.  See the December 2009 ASHRAE Journal Article “A Closer Look at Chiller Ratings” for a more complete discussion of IPLV and it use.

  • Where are the weather zone maps? I do not see them.

      You must first select a Region and a Country from the drop down menus.  The appropriate weather zone map for that location will then be displayed.

  • What does changing the UOM (IP or SI) do?

      Changing the UOM (Unit of Measure) converts all user inputs on the myPLV Calculator tab to the new unit of measure, and changes all labels and references depicting a unit of measure to the appropriate convention.  Cooling capacity is listed in either Tons or kW; temperatures are listed in either °F or °C; and efficiency is listed as kW/Ton or kW/kW, depending on UOM selected.

      Note: User entered load and weather data on the "Custom Load" tab is not converted in this manner as this could result in user entered data being overwritten unintentionally.

  • What if I want to use my own load and weather data?

      If checked, the checkbox next to the "Region" drop-down list will expose the "Custom Load" tab allowing users to enter custom building load and weather data for 8760 hours comprising one calendar year.

      Note: When the building load and weather data are calculated by this tool for a selected location in the myPLVTM calculator worksheet, the data is copied to the "Custom Load" tab both for reference and as a starting point for user provided custom load and weather data.

  • Why do all of the values go to zero when I change an input such as building type?

      This occurs to force the user to re-calculate, ensuring that correct outputs for the input values are shown.

  • Why are the same results calculated if I choose my building in Jacksonville, FL or Orlando, FL?

      The user entry for City is used to map to the appropriate climatic zones (see the ClimateZones tab).  The building load is generalized to that climatic zone rather than to the specific city.  Load profiles are output from the Energy Plus simulation program created by Pacific Northwest National Labs (PNNL) for use in justifying the new ASHRAE Standard 90.1 (2010) efficiency levels and represent various building types in 20 climatic zones per ASHRAE Standard 169-2013.

  • What if my city is not in the list?

      Select a city from the list that is in the same climatic zone.  To identify the correct zone, first locate your location on the blue climate zone map tab which is shown based on the country selected.  Then in the "Region" drop-down box, select "By Climate Zone".  This action will change the "Country" drop-down box to "Climate Zone", allowing you to select the desired climate zone from the list.

  • What if my building is not on the list of Building Types?

      If your specific building is not on the list, choose a building type with characteristics and an operating schedule similar to your building.  The load profiles are partly based on occupancy assumptions within the EnergyPlusTM models and details can be found on the “energy codes” website (a link is given in this FAQ section).  The occupancy for various building types may be generalized as follows:

      Office – 12 hour operation; 5 days a week

      Hospital – 24 hour operation; 7 days a week; heavier occupancy during the day

      High Rise Apts – 24 hour operation; 7 days a week; lighter occupancy during the day

      Primary School – 12 hour operation; 5 days a week; seasonal

      Secondary School – 12 hour operation; 5 days a week; seasonal

      Hotel – 24 hour operation; 7 days a week

  • What load profiles does myPLV use?

      The building load profiles included in the myPLVTM tool are generated from the public domain EnergyPlus files.  These files were developed by Pacific Northwest National Labs (PNNL) for energy analysis work in conjunction with and with oversight from ASHRAE for the development of ASHRAE/IES 90.1-2010 Energy Standard for Buildings Except Low-Rise Residential Buildings.  The web site for the PNNL files can be found at http://www.energycodes.gov/development/commercial/90.1_models.

  • Please provide more information on on how to use the input data set for the tower performance section
    in the condenser water design flow rate optimization worksheet.

      The simulation in the condenser water flow optimization worksheet assumes the user typically selects chillers for use at 3 gpm/ton condenser water flow.  In order to perform an energy comparison, the 3 gpm/ton condition is used as a starting point and the tower performance is entered as typical for your location.   Note the first two lines are not user entered data (orange cells) – they are informational only and describe the wet bulb conditions for the user selected reference city supplying the TMY zone data.  Note that the chiller entering condenser water design temperature is critical to the chiller selection and the tower performance and control must be able to supply a condenser water temperature that does not cause the chiller operating problems.

      Example data set for the “Tower Selection Conditions at 3 gpm/ton”

       

      Data Point Label

       

      Value

      Explanation

      Design wet bulb for Weather zone data, 0.4% humidity

      78.1 F

      This data is auto selected and is only used as informational display.   It is the 0.4% ASHRAE wet bulb value for the reference city of the selected zone

       

      Maximum wet bulb for weather zone data

      81.8 F

      This data is auto selected and is only used as informational display.   This data point is the observed maximum wet bulb in the TMY data set for the selected zone.

       

      Enter the design wet bulb for the cooling tower selection associated with 3 gpm/ton operation

       

      78 F

      User entered data point.  A typical entry might be 78F, however it needs to represent your location!

      Tower design approach

      7F

      User entered data point.  A typical value is a 7F degree approach.

       

      Chiller Design Entering Condenser water temperature

      85F

      User entered data point.  Often times this is just the design wet bulb added to the design approach (rows 3 and 4).  But it can be higher if the user wants to add in a bit of design margin after reflecting on the maximum encountered wet bulb (row 2).

       

      Condenser pump design pressure rise

      80 ft H2O

      User entered data point.  This is the pump pressure rise that would be expected when the entire plant is operating at design loads.  The energy simulation assumes that some of the pressure drop components in the hydronic system will significantly reduce when the plant operates at lower flow rates.

  • What is meant by chiller design efficiency at standard AHRI conditions in the Condenser Water Flow Optimization
    worksheet and how is this used?

      The standard rating conditions for AHRI water-cooled product are 44F leaving chilled water temperature, a 2.4 gpm/ton evaporator water flow, 85F entering condenser water temperature, and a 3 gpm/ton condenser water flow.  Based on the user entered chiller performance (kW/ton) at these conditions the program will estimate the expected same chiller design performance at each new selection condition for each flow.  This revised efficiency is displayed on the condenser water flow optimization table.

  • How are ton-hrs calculated?

      The myPLVTM tool uses the EnergyPlusTM load profiles created by PNNL.  The PNNL load profiles provide the tonnage for each of the 8,760 hours per year.  The myPLVTM tool places each load value into the proper bin and sums up the total ton-hrs for each bin range.  The total ton-hrs is the sum of the ton-hrs for all (4) bins.

  • How is the percent weighting calculated?

      The percent weighting is determined from the ton-hrs in each bin.  The calculation is as follows:

                      [ton-hrs within that bin]  x 100%  /  [total annual ton-hrs]

  • How is the entering condenser temperature calculated for each bin?

      Water-cooled solution:  For every hour there is a load and a corresponding entering condenser water temperature that is calculated based on the coincident wet bulb and the tower approach at that hour as computed by the cooling tower control method selected.  Each entering condenser temperature is weighted by that hour's load value and summed with other weighted temperatures within that bin.  This overall sum is divided by the ton-hrs for that bin to get an overall weighted entering condenser water temperature.

      Air-cooled solution:  The methodology is similar to the water-cooled solution; however, the outdoor ambient dry-bulb temperature is used directly as the entering condenser temperature since cooling tower performance need not be taken into account.

  • How is myPLV calculated?

      Water-cooled kW/ton:   myPLVTM is calculated in the same fashion as IPLV:

                      myPLV = 1/[a/A + b/B + c/C + d/D]

      ...where the lower case letters are the decimal values for weighting, and the upper case letters are the chiller kw/ton for that bin at the myPLVTM conditions.

      Air-cooled EER:  myPLVTM EER  is calculated in the same fashion as IPLV:

                      myPLVTM EER = a*A + b*B + c*C + d*D

  • How is Annualized kW-hrs computed in the myPLV bid form?

      Water-cooled:    The ton-hrs value in each bin is multiplied by its respective kW/ton performance and the (4) bins are summed together.

      Air-cooled:   The ton-hrs value in each bin is multiplied by 12 and divided by respective EER value, then the (4) bins are summed together.

  • What is the annualized kW-hrs used for?

      The annual kW-hrs can be used on the Bid Form tab to determine the operating costs of different chiller options.  These electrical operating costs include both the demand ($/kW) and the energy consumption ($/kWh).

  • How is the demand charge calculated?

      Water-cooled:  The demand is calculated by first establishing the highest tonnage for any given hour within each month.  If any given month has a tonnage that is less than the ratchet rate multiplied by the peak for the year, then peak tons for that month are set to the ratchet rate multiplied by the peak tons for the year.  The peaks for each month are summed together and multiplied by the design kW/ton for that chiller and the demand rate for the plant.  Note that this results in an approximation for the peak kW value for each month but simplifies the process by not requiring chiller performance values coincident with each peak condition for each month.

      Air-cooled:  The process is similar to the water-cooled plant with the appropriate modifications to handle the different units for EER.

  • What is the Ratchet Rate?

      Ratchet rate is a term to describe minimum demand charges imposed by a utility company against peak power usage.  For example, your building hit a peak power use of 500 kW in August and you have a ratchet rate of 50%, you will be charged at minimum for a 250 kW demand every month.  Therefore, if your peak power use in January was only 100 kW, you would still be charge for a demand of 250 kW.  A ratchet rate is common with many utility companies.

  • How is simple payback determined in the bid form worksheet?

      Simple payback is calculated by taking the price difference of an Option compared to the Base and then dividing that by the savings delta for Total Annual Energy Charge.

  • Some parts of the application do not function properly. Is there something I can do?

      This application requires linkage to various system libraries.  In order to resolve these references, the application macros must be allowed to run in the background and excel must be set up properly to let this happen.  Enabling macros at program start is not sufficient, the trust center in Microsoft Excel must be set up to accommodate program execution of these macros.  To do this for Excel 2010 and 2013 …

      Start excel and select the “File” drop down menu

      Select “options”  and then select “Trust Center”

      Press the “Trust Center Selections…” button

      Select the “Macro Settings” from the selection list

      The following 2 checkboxes need to be set:

      - Enable all macros

      - Trust access to the VBA project object model

      Press OK and exit Excel

      You can now run the myPLV application.