Class: OpenStudio::Model::WaterHeaterMixed

Inherits:
Object
  • Object
show all
Defined in:
lib/openstudio-standards/standards/Standards.WaterHeaterMixed.rb,
lib/openstudio-standards/hvac_sizing/Siz.WaterHeaterMixed.rb

Overview

open the class to add methods to return sizing values @Todo: currently OpenStudio is missing the WaterHeater:Sizing object, so unlikely to need it right now…

Instance Method Summary collapse

Instance Method Details

#apply_efficiency(template) ⇒ Bool

Applies the standard efficiency ratings and typical losses and paraisitic loads to this object. Efficiency and skin loss coefficient (UA) Per PNNL www.energycodes.gov/sites/default/files/documents/PrototypeModelEnhancements_2014_0.pdf Appendix A: Service Water Heating

Parameters:

  • template (String) —

    valid choices: ‘DOE Ref Pre-1980’, ‘DOE Ref 1980-2004’, ‘90.1-2004’, ‘90.1-2007’, ‘90.1-2010’, ‘90.1-2013’

  • standards (Hash) —

    the OpenStudio_Standards spreadsheet in hash format

Returns:

  • (Bool) —

    true if successful, false if not



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# File 'lib/openstudio-standards/standards/Standards.WaterHeaterMixed.rb', line 12

def apply_efficiency(template)
  # Get the capacity of the water heater
  # TODO add capability to pull autosized water heater capacity
  # if the Sizing:WaterHeater object is ever implemented in OpenStudio.
  capacity_w = heaterMaximumCapacity
  if capacity_w.empty?
    OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.WaterHeaterMixed', "For #{name}, cannot find capacity, standard will not be applied.")
    return false
  else
    capacity_w = capacity_w.get
  end
  capacity_btu_per_hr = OpenStudio.convert(capacity_w, 'W', 'Btu/hr').get
  capacity_kbtu_per_hr = OpenStudio.convert(capacity_w, 'W', 'kBtu/hr').get

  # Get the volume of the water heater
  # TODO add capability to pull autosized water heater volume
  # if the Sizing:WaterHeater object is ever implemented in OpenStudio.
  volume_m3 = tankVolume
  if volume_m3.empty?
    OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.WaterHeaterMixed', "For #{name}, cannot find volume, standard will not be applied.")
    return false
  else
    volume_m3 = volume_m3.get
  end
  volume_gal = OpenStudio.convert(volume_m3, 'm^3', 'gal').get

  # Get the heater fuel type
  fuel_type = heaterFuelType
  unless fuel_type == 'NaturalGas' || fuel_type == 'Electricity'
    OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.WaterHeaterMixed', "For #{name}, fuel type of #{fuel_type} is not yet supported, standard will not be applied.")
  end

  # Calculate the water heater efficiency and
  # skin loss coefficient (UA)
  # Calculate the energy factor (EF)
  # From PNNL http://www.energycodes.gov/sites/default/files/documents/PrototypeModelEnhancements_2014_0.pdf
  # Appendix A: Service Water Heating
  water_heater_eff = nil
  ua_btu_per_hr_per_f = nil
  sl_btu_per_hr = nil
  case fuel_type
  when 'Electricity'
    case template
    when 'DOE Ref Pre-1980', 'DOE Ref 1980-2004', '90.1-2004', '90.1-2007', '90.1-2010', '90.1-2013'

      if capacity_w <= 12_000 # I think this should be 12000W, use variable capacity_w instead of capacity_btu_per_hr (as per PNNL doc)
        # Fixed water heater efficiency per PNNL
        water_heater_eff = 1
        # Calculate the minimum Energy Factor (EF)
        base_ef, vol_drt = case template
                           when 'DOE Ref Pre-1980', 'DOE Ref 1980-2004', '90.1-2004', '90.1-2007'
                             [0.93, 0.00132]
                           when '90.1-2010'
                             [0.97, 0.00132]
                           when '90.1-2013'
                             [0.97, 0.00035]
                           end

        ef = base_ef - (vol_drt * volume_gal)
        # Calculate the skin loss coefficient (UA)
        ua_btu_per_hr_per_f = (41_094 * (1 / ef - 1)) / (24 * 67.5)
      else
        # Fixed water heater efficiency per PNNL
        water_heater_eff = 1
        # Calculate the skin loss coefficient (UA)
        case template
        when 'DOE Ref Pre-1980', 'DOE Ref 1980-2004', '90.1-2004', '90.1-2007', '90.1-2010'
          # Calculate the max allowable standby loss (SL)
          sl_btu_per_hr = 20 + (35 * Math.sqrt(volume_gal)) 
          # Calculate the skin loss coefficient (UA)
          ua_btu_per_hr_per_f = sl_btu_per_hr / 70
        when '90.1-2013'
          # Calculate the percent loss per hr
          hrly_loss_pct = (0.3 + 27 / volume_gal) / 100
          # Convert to Btu/hr, assuming:
          # Water at 120F, density = 8.25 lb/gal
          # 1 Btu to raise 1 lb of water 1 F
          # Therefore 8.25 Btu / gal of water * deg F
          # 70F delta-T between water and zone
          hrly_loss_btu_per_hr = hrly_loss_pct * volume_gal * 8.25 * 70
          # Calculate the skin loss coefficient (UA)
          ua_btu_per_hr_per_f = hrly_loss_btu_per_hr / 70
        end
      end

    when 'NECB 2011'
      volume_l_per_s = volume_m3 * 1000
      if capacity_btu_per_hr <= OpenStudio.convert(12, 'kW', 'Btu/hr').get
        # Fixed water heater efficiency per PNNL
        water_heater_eff = 1
        # Calculate the max allowable standby loss (SL)
        sl_w = if volume_l_per_s < 270
                 40 + 0.2 * volume_l_per_s # assume bottom inlet
               else
                 0.472 * volume_l_per_s - 33.5
               end # assume bottom inlet
        sl_btu_per_hr = OpenStudio.convert(sl_w, 'W', 'Btu/hr').get
      else
        # Fixed water heater efficiency per PNNL
        water_heater_eff = 1
        # Calculate the max allowable standby loss (SL)   # use this - NECB does not give SL calculation for cap > 12 kW
        sl_btu_per_hr = 20 + (35 * Math.sqrt(volume_gal))
      end
      # Calculate the skin loss coefficient (UA)
      ua_btu_per_hr_per_f = sl_btu_per_hr / 70
    end

  when 'NaturalGas'
    case template # TODO: inconsistency; ref buildings don't calculate water heater UA the same way
    when 'DOE Ref Pre-1980', 'DOE Ref 1980-2004'
      water_heater_eff = 0.78
      ua_btu_per_hr_per_f = 11.37
    when '90.1-2004', '90.1-2007', '90.1-2010', '90.1-2013', 'NECB 2011'
      if capacity_btu_per_hr <= 75_000
        # Fixed water heater thermal efficiency per PNNL
        water_heater_eff = 0.82
        # Calculate the minimum Energy Factor (EF)
        base_ef, vol_drt = case template
                           when '90.1-2004', '90.1-2007'
                             [0.62, 0.0019]
                           when '90.1-2010', 'NECB 2011'
                             [0.67, 0.0019]
                           when '90.1-2013'
                             [0.67, 0.0005]
                           end

        ef = base_ef - (vol_drt * volume_gal)
        # Calculate the Recovery Efficiency (RE)
        # based on a fixed capacity of 75,000 Btu/hr
        # and a fixed volume of 40 gallons by solving
        # this system of equations:
        # ua = (1/.95-1/re)/(67.5*(24/41094-1/(re*cap)))
        # 0.82 = (ua*67.5+cap*re)/cap
        cap = 75_000.0
        re = (Math.sqrt(6724 * ef**2 * cap**2 + 40_409_100 * ef**2 * cap - 28_080_900 * ef * cap + 29_318_000_625 * ef**2 - 58_636_001_250 * ef + 29_318_000_625) + 82 * ef * cap + 171_225 * ef - 171_225) / (200 * ef * cap)
        # Calculate the skin loss coefficient (UA)
        # based on the actual capacity.
        ua_btu_per_hr_per_f = (water_heater_eff - re) * capacity_btu_per_hr / 67.5
      else
        # Thermal efficiency requirement from 90.1
        et = 0.8
        # Calculate the max allowable standby loss (SL)
        cap_adj, vol_drt = case template
                 when '90.1-2004', '90.1-2007', '90.1-2010', 'NECB 2011'
                   [800, 110]
                 when '90.1-2013'
                   [799, 16.6]
                 end
        sl_btu_per_hr = (capacity_btu_per_hr / cap_adj + vol_drt * Math.sqrt(volume_gal))
        # Calculate the skin loss coefficient (UA)
        ua_btu_per_hr_per_f = (sl_btu_per_hr * et) / 70
        # Calculate water heater efficiency
        water_heater_eff = (ua_btu_per_hr_per_f * 70 + capacity_btu_per_hr * et) / capacity_btu_per_hr
      end
    end
  end

  # Convert to SI
  ua_btu_per_hr_per_c = OpenStudio.convert(ua_btu_per_hr_per_f, 'Btu/hr*R', 'W/K').get

  # Set the water heater properties
  # Efficiency
  setHeaterThermalEfficiency(water_heater_eff)
  # Skin loss
  setOffCycleLossCoefficienttoAmbientTemperature(ua_btu_per_hr_per_c)
  setOnCycleLossCoefficienttoAmbientTemperature(ua_btu_per_hr_per_c)
  # TODO: Parasitic loss (pilot light)
  # PNNL document says pilot lights were removed, but IDFs
  # still have the on/off cycle parasitic fuel consumptions filled in
  setOnCycleParasiticFuelType(fuel_type)
  # self.setOffCycleParasiticFuelConsumptionRate(??)
  setOnCycleParasiticHeatFractiontoTank(0)
  setOffCycleParasiticFuelType(fuel_type)
  # self.setOffCycleParasiticFuelConsumptionRate(??)
  setOffCycleParasiticHeatFractiontoTank(0.8)

  # set part-load performance curve
  if template == 'NECB 2011' && fuel_type == 'NaturalGas'
    plf_vs_plr_curve = model.add_curve('SWH-EFFFPLR-NECB2011')
    setPartLoadFactorCurve(plf_vs_plr_curve)
  end

  # Append the name with standards information
  setName("#{name} #{water_heater_eff.round(3)} Therm Eff")
  OpenStudio.logFree(OpenStudio::Info, 'openstudio.model.WaterHeaterMixed', "For #{template}: #{name}; thermal efficiency = #{water_heater_eff.round(3)}, skin-loss UA = #{ua_btu_per_hr_per_f.round}Btu/hr")

  return true
end

#apply_prm_baseline_fuel_type(template, building_type) ⇒ Bool

Applies the correct fuel type for the water heaters in the baseline model. For most standards and for most building types, the baseline uses the same fuel type as the proposed. However, certain standards like 90.1-2013 require a change in some scenarios.

Parameters:

  • building_type (String) —

    the building type

Returns:

  • (Bool) —

    returns true if successful, false if not.



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# File 'lib/openstudio-standards/standards/Standards.WaterHeaterMixed.rb', line 209

def apply_prm_baseline_fuel_type(template, building_type)
  # For all standards except 90.1-2013
  # baseline is same as proposed per
  # Table G3.1 item 11.b
  unless template == '90.1-2013'
    return true
  end

  # Determine the building-type specific
  # fuel requirements from Table G3.1.1-2
  new_fuel = nil
  case building_type
  when 'SecondarySchool', 'PrimarySchool', # School/university
       'SmallHotel', # Motel
       'LargeHotel', # Hotel
       'QuickServiceRestaurant', # Dining: Cafeteria/fast food
       'FullServiceRestaurant', # Dining: Family
       'MidriseApartment', 'HighriseApartment', # Multifamily
       'Hospital', # Hospital
       'Outpatient' # Health-care clinic
    new_fuel = 'NaturalGas'
  when 'SmallOffice', 'MediumOffice', 'LargeOffice', # Office
       'RetailStandalone', 'RetailStripmall', # Retail
       'Warehouse' # Warehouse
    new_fuel = 'Electricity'
  else
    new_fuel = 'NaturalGas'
  end

  # Change the fuel type if necessary
  old_fuel = heaterFuelType
  unless new_fuel == old_fuel
    setHeaterFuelType(new_fuel)
    OpenStudio.logFree(OpenStudio::Info, 'openstudio.standards.WaterHeaterMixed', "For #{name}, changed baseline water heater fuel from #{old_fuel} to #{new_fuel}.")
  end

  return true
end

#autosizedHeaterMaximumCapacity ⇒ Object

returns the autosized Heater Maximum Capacity as an optional double



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# File 'lib/openstudio-standards/hvac_sizing/Siz.WaterHeaterMixed.rb', line 8

def autosizedHeaterMaximumCapacity

  # @Todo: check the correct syntax here
  return self.model.getAutosizedValue(self, 'Design Size Nominal Capacity', 'W')

end

#find_capacity ⇒ Double

Finds capacity in Btu/hr

Returns:

  • (Double) —

    capacity in Btu/hr to be used for find object



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# File 'lib/openstudio-standards/standards/Standards.WaterHeaterMixed.rb', line 251

def find_capacity()

  # Get the coil capacity
  capacity_w = nil
  if self.heaterMaximumCapacity.is_initialized
    capacity_w = self.heaterMaximumCapacity.get
  elsif self.autosizedHeaterMaximumCapacity.is_initialized
    capacity_w = self.autosizedHeaterMaximumCapacity.get
  else
    OpenStudio::logFree(OpenStudio::Warn, 'openstudio.standards.WaterHeaterMixed', "For #{self.name} capacity is not available.")
    return false
  end

  # Convert capacity to Btu/hr
  capacity_btu_per_hr = OpenStudio.convert(capacity_w, "W", "Btu/hr").get

  return capacity_btu_per_hr

end