# Reopen the OpenStudio class to add methods to apply standards to this object
class OpenStudio::Model::WaterHeaterMixed
# Applies the standard efficiency ratings and typical losses and paraisitic loads to this object.
# Efficiency and skin loss coefficient (UA)
# Per PNNL http://www.energycodes.gov/sites/default/files/documents/PrototypeModelEnhancements_2014_0.pdf
# Appendix A: Service Water Heating
#
# @param template [String] valid choices: 'DOE Ref Pre-1980', 'DOE Ref 1980-2004', '90.1-2004', '90.1-2007', '90.1-2010', '90.1-2013'
# @param standards [Hash] the OpenStudio_Standards spreadsheet in hash format
# @return [Bool] true if successful, false if not
# @todo break parasitic/skin losses into a separate method in
# Prototype.WaterHeaterMixed because not governed by standard?
def setStandardEfficiency(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 = self.heaterMaximumCapacity
if capacity_w.empty?
OpenStudio::logFree(OpenStudio::Warn, "openstudio.standards.WaterHeaterMixed", "For #{self.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 = self.tankVolume
if volume_m3.empty?
OpenStudio::logFree(OpenStudio::Warn, "openstudio.standards.WaterHeaterMixed", "For #{self.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 = self.heaterFuelType
if !(fuel_type == 'NaturalGas' || fuel_type == 'Electricity')
OpenStudio::logFree(OpenStudio::Warn, "openstudio.standards.WaterHeaterMixed", "For #{self.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 <= 12000 # 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)
ef = 0.97 - (0.00132 * volume_gal)
# Calculate the skin loss coefficient (UA)
ua_btu_per_hr_per_f = (41094*(1/ef - 1))/(24*67.5)
else
# Fixed water heater efficiency per PNNL
water_heater_eff = 1
# 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
end
when 'NECB 2011'
volume_l_per_s = volume_m3 * 1000
if capacity_w <= 12000
# Fixed water heater efficiency per PNNL
water_heater_eff = 1
# Calculate the max allowable standby loss (SL)
if volume_l_per_s < 270
sl_w = 40 + 0.2 * volume_l_per_s # assume bottom inlet
else
sl_w = 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 <= 75000
# Fixed water heater efficiency per PNNL
water_heater_eff = 0.82
# Calculate the minimum Energy Factor (EF)
ef = 0.67 - (0.0019 * volume_gal)
# Calculate the skin loss coefficient (UA)
# TODO solve system of equations {u = (1/.95-1/r)/(67.5*(24/41094-1/(r*75000))), 0.82 = (u*67.5+75000*r)/75000}
# Assume recovery efficieny = 0.81 based on regression of prototype models instead
re = 0.81
ua_btu_per_hr_per_f = (1/ef-1/re)/(67.5*(24/41094-1/(re*capacity_btu_per_hr)))
else
# Thermal efficiency requirement from 90.1
et = 0.8
# Calculate the max allowable standby loss (SL)
sl_btu_per_hr = et*(capacity_btu_per_hr/800 + 110*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
self.setHeaterThermalEfficiency(water_heater_eff)
# Skin loss
self.setOffCycleLossCoefficienttoAmbientTemperature(ua_btu_per_hr_per_c)
self.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
self.setOnCycleParasiticFuelType(fuel_type)
#self.setOffCycleParasiticFuelConsumptionRate(??)
self.setOnCycleParasiticHeatFractiontoTank(0)
self.setOffCycleParasiticFuelType(fuel_type)
#self.setOffCycleParasiticFuelConsumptionRate(??)
self.setOffCycleParasiticHeatFractiontoTank(0.8)
# Append the name with standards information
self.setName("#{name} #{water_heater_eff.round(3)}Eff")
OpenStudio::logFree(OpenStudio::Info, 'openstudio.model.WaterHeaterMixed', "For #{template}: #{self.name}; efficiency = #{water_heater_eff.round(3)}, skin-loss UA = #{ua_btu_per_hr_per_f.round}Btu/hr AKA #{ua_btu_per_hr_per_c.round(1)}W/K")
return true
end
end