Load Calculation v2 - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 13.1

Controller Tool Help
Product
Controls > Control Tools > Controller Configuration Tool
Document type
User Guide
Document number
LIT-12011147
Version
13.1
Revision date
2019-12-04
Important: As of Release 3.0, the Load Calculation v2 module replaces the Calculate Building Load module.

The Load Calculation module provides the logic necessary to evaluate cold and hot water loads. The module inputs include system flow, supply and return temperatures media, a Heating or Cooling Switch, and glycol concentration. This module considers Pure water, Water-Ethylene Glycol solution, and Water-Propylene Glycol solution. You can select the media and the concentration of Glycol in percentage, as necessary. The output of this module is the heating or cooling heat transfer rate. A positive output value in the Heating mode indicates a heating load and a positive output value in the Cooling mode indicates a cooling load.

The required physical properties (density and heat capacity) are calculated for water as functions of temperature. The Glycol solutions are calculated as functions of both temperature and concentration according to the following equations.

Load Calculation

Load is calculated according to the following equation.

Load = Flow x 10-3 x ρ x Cp x Δ T

where

  • Flow: Volumetric Flow [gpm input converted to l/s]

  • ρ: Density [kg/m3]

  • c p : Specific Heat Capacity [kJ/kg-˚C]

  • ΔT: Temperature Differential (Treturn - Tsupply ) [˚F input converted to˚C]

Load Calculation Computations

The Load Calculation Standard Object computes heating/cooling loads if the heat transfer media is one of the following:

  • Water

  • Water-Ethylene Glycol solution

  • Water-Propylene Glycol solution

If you choose Water, the density ( ρ ) and specific heat (Cp) are calculated using the following equations:

ρ = R(1) + R(2)*T +R(3)*T^2

Cp = C(1) + C(2)*T +C(3)*T^2

where

  • ρ in kg/m^3

  • Cp in kJ/kg-K

  • T in ˚C. Range of applicability is 0 to 226.85 ˚C.

constants

  • R(1) = 1002.346

  • R(2) = -0.1811972

  • R(3) = -0.002543243

  • C(1) = 4.211899

  • C(2) = -0.001419488

  • C(3) = 0.00001446954

If you choose any of the solutions, the concentration in volume percent of the Glycol (either Ethylene or Propylene) should be provided. In these two cases, two properties are calculated as a function of both Temperature and Composition, using the following equations:

ρ = R(1) + R(2)*T +R(3)*Comp +R(4)*T*Comp +R(5)*T^2 +R(6)*Comp^2

Cp = C(1) + C(2)*T +C(3)*Comp +C(4)*T*Comp +C(5)*T^2 +C(6)*Comp^2

where

  • ρ in kg/m^3

  • Cp in kJ/kg-K

  • T in ˚C. Range of applicability -35 to 125 ˚C

Composition is in decimals, for example, 10% is 0.1.

The range of applicability is 0.1 to 0.9.

Ethylene Glycol:

  • R(1) = 1000.993

  • R(2) = -0.1820508

  • R(3) = 180.1828

  • R(4) = -0.3142169

  • R(5) = -0.002448466

  • R(6) = -39.50314

  • C(1) = 4.090844

  • C(2) = 0.001329405

  • C(3) = -1.5259387

  • C(4) = 0.005028424

  • C(5) = -0.0000001239507

  • C(6) = -0.4911836

Propylene Glycol:

  • R(1) = 1004.741

  • R(2) = -0.2981901

  • R(3) = 126.9451

  • R(4) = -0.4054804

  • R(5) = -0.001850845

  • R(6) = -61.60746

  • C(1) = 4.12479074756495

  • C(2) = 0.00105318162514

  • C(3) = -0.73136943192630

  • C(4) = 0.00559981967494

  • C(5) = 0.00000004392872

  • C(6) = -1.21562837961674

Important: Since the preceding equations are curve fits of experimental data, these equations cannot and should not be used beyond the stated range of applicability.

You can view and modify the modules in this group’s logic.