Fix PTHP capacity and VAV minimum damper calculation issues

lib/openstudio-standards/standards/Standards.AirLoopHVAC.rb

@@ -2080,7 +2080,7 @@ def air_loop_hvac_adjust_minimum_vav_damper_positions(air_loop_hvac)
           v_pz = clg_dsn_flow
         end
       else
-        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}: #{zone.name} clg_dsn_flow could not be found.")
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}: #{zone.name}, zone CoolingDesignAirFlowRate could not be found.")
       end
       htg_dsn_flow = zone.autosizedHeatingDesignAirFlowRate
       if htg_dsn_flow.is_initialized
@@ -2089,7 +2089,11 @@ def air_loop_hvac_adjust_minimum_vav_damper_positions(air_loop_hvac)
           v_pz = htg_dsn_flow
         end
       else
-        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}: #{zone.name} htg_dsn_flow could not be found.")
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}: #{zone.name}, zone HeatingDesignAirFlowRate could not be found.")
+      end
+
+      if v_pz.zero?
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}: #{zone.name}, neither the CoolingDesignAirFlowRate nor the HeatingDesignAirFlowRate could be found. The primary design air flow rate, v_pz, is zero. The zone may be missing a DesignSpecificationOutdoorAir object, or both heating and cooling load may be zero.")
       end
 
       # Get the minimum damper position
@@ -2135,7 +2139,7 @@ def air_loop_hvac_adjust_minimum_vav_damper_positions(air_loop_hvac)
       v_dz = v_pz * mdp
 
       # Zone discharge air fraction
-      z_d = v_oz / v_dz
+      z_d = v_dz.zero? || v_oz.zero? ? 0.0 : v_oz / v_dz
 
       # Zone ventilation effectiveness
       e_vz = 1.0 + x_s - z_d
@@ -2157,7 +2161,8 @@ def air_loop_hvac_adjust_minimum_vav_damper_positions(air_loop_hvac)
         v_dz_adj = v_oz / z_d_adj
 
         # Adjusted minimum damper position
-        mdp_adj = v_dz_adj / v_pz
+        # default to 0.2 if either values are zero
+        mdp_adj = v_dz_adj.zero? || v_pz.zero? ? 0.2 : v_dz_adj / v_pz
 
         # Don't allow values > 1
         if mdp_adj > 1.0

lib/openstudio-standards/standards/Standards.CoilHeatingDXSingleSpeed.rb

@@ -133,12 +133,23 @@ def coil_heating_dx_single_speed_standard_minimum_cop(coil_heating_dx_single_spe
       # TABLE 6.8.1D
       # COP = pthp_cop_coeff_1 - (pthp_cop_coeff_2 * Cap / 1000)
       # Note c: Cap means the rated cooling capacity of the product in Btu/h.
-      # If the unit's capacity is less than 7000 Btu/h, use 7000 Btu/h in the calculation.
-      # If the unit's capacity is greater than 15,000 Btu/h, use 15,000 Btu/h in the calculation.
-      capacity_btu_per_hr = 7000 if capacity_btu_per_hr < 7000
-      capacity_btu_per_hr = 15_000 if capacity_btu_per_hr > 15_000
+
+      # If the unit's capacity is nil or less than 7000 Btu/h, use 7000 Btu/h in the calculation
+      # If the unit's capacity is greater than 15,000 Btu/h, use 15,000 Btu/h in the calculation
+      if capacity_btu_per_hr.nil?
+        capacity_btu_per_hr = 7000.0
+        capacity_kbtu_per_hr = capacity_btu_per_hr / 1000.0
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.CoilHeatingDXSingleSpeed', "For PTHP units, 90.1 heating efficiency depends on paired cooling capacity. Cooling Capacity for #{coil_heating_dx_single_speed.name}: #{sub_category} is nil. This zone may not have heating. Using default equipment efficiency for a 7 kBtu/hr unit.")
+      elsif capacity_btu_per_hr < 7000
+        capacity_btu_per_hr = 7000.0
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.CoilHeatingDXSingleSpeed', "For PTHP units, 90.1 heating efficiency depends on paired cooling capacity. Cooling Capacity for #{coil_heating_dx_single_speed.name}: #{sub_category} is #{capacity_btu_per_hr.round} Btu/hr, which is less than the typical minimum equipment size of 7 kBtu/hr. Using default equipment efficiency for a 7 kBtu/hr unit.")
+      elsif capacity_btu_per_hr > 15_000
+        OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.CoilHeatingDXSingleSpeed', "For PTHP units, 90.1 heating efficiency depends on paired cooling capacity. Cooling Capacity for #{coil_heating_dx_single_speed.name}: #{sub_category} is #{capacity_btu_per_hr.round} Btu/hr, which is more than the typical maximum equipment size of 15 kBtu/hr. Using default equipment efficiency for a 15 kBtu/hr unit.")
+        capacity_btu_per_hr = 15_000.0
+      end
+
       min_coph = pthp_cop_coeff_1 - (pthp_cop_coeff_2 * capacity_btu_per_hr / 1000.0)
-      cop = cop_heating_to_cop_heating_no_fan(min_coph, OpenStudio.convert(capacity_kbtu_per_hr, 'kBtu/hr', 'W').get)
+      cop = cop_heating_to_cop_heating_no_fan(min_coph, OpenStudio.convert(capacity_btu_per_hr, 'Btu/hr', 'W').get)
       new_comp_name = "#{coil_heating_dx_single_speed.name} #{capacity_kbtu_per_hr.round} Clg kBtu/hr #{min_coph.round(1)}COPH"
       OpenStudio.logFree(OpenStudio::Info, 'openstudio.standards.CoilHeatingDXSingleSpeed', "For #{coil_heating_dx_single_speed.name}: #{sub_category} Cooling Capacity = #{capacity_kbtu_per_hr.round}kBtu/hr; COPH = #{min_coph.round(2)}")
     end