# Baseline Service Water-Heating Systems This page defines the baseline service water heating systems required by ASHRAE 90.1 Performance Rating Method (PRM) Appendix G. The system selection is based on building area type per Table G3.1.1-2. ## System Selection Table ### **ASHRAE 90.1 Baseline Service Water Heating Systems** | Building Area Type | Baseline Heating Method | | ------------------------------------------------------ | ---------------------------------------- | | **System A: Gas Storage Water Heater** | | | Automotive facility | Gas storage water heater | | Dining: Bar lounge/leisure | Gas storage water heater | | Dining: Cafeteria/fast food | Gas storage water heater | | Dining: Family | Gas storage water heater | | Dormitory | Gas storage water heater | | Exercise center | Gas storage water heater | | Fire station | Gas storage water heater | | Grocery store | Gas storage water heater | | Gymnasium | Gas storage water heater | | Hospital and outpatient surgery center | Gas storage water heater | | Hotel | Gas storage water heater | | Manufacturing facility | Gas storage water heater | | Motel | Gas storage water heater | | Multifamily | Gas storage water heater | | Penitentiary | Gas storage water heater | | Performing arts theater | Gas storage water heater | | School/university | Gas storage water heater | | Sports arena | Gas storage water heater | | All others | Gas storage water heater | | **System B: Electric Resistance Storage Water Heater** | | | Convenience store | Electric resistance storage water heater | | Courthouse | Electric resistance storage water heater | | Convention center | Electric resistance storage water heater | | Health-care clinic | Electric resistance storage water heater | | Library | Electric resistance storage water heater | | Motion picture theater | Electric resistance storage water heater | | Museum | Electric resistance storage water heater | | Office | Electric resistance storage water heater | | Parking garage | Electric resistance storage water heater | | Police station | Electric resistance storage water heater | | Post office | Electric resistance storage water heater | | Religious facility | Electric resistance storage water heater | | Retail | Electric resistance storage water heater | | Town hall | Electric resistance storage water heater | | Transportation | Electric resistance storage water heater | | Warehouse | Electric resistance storage water heater | | Workshop | Electric resistance storage water heater | ## Detailed System Descriptions ### System A: Gas Storage Water Heater **Component Configuration** **Primary Heating Component:** * Storage Tank: Insulated steel tank (50-100 gallons typical) * Heating Element: Gas-fired burner with combustion chamber * Thermostat: Dual setpoint control (upper and lower elements) * Safety Relief: Pressure and temperature relief valve **Distribution System:** * Circulation Pump: Constant speed pump for hot water distribution * Supply Piping: Insulated copper or PEX (minimum R-3.5 insulation) * Return Piping: Optional circulation return or drain connection * Expansion Tank: Accommodates thermal expansion (10% of tank volume) * Check Valve: Prevents backflow from building to supply **Performance Characteristics:** * Thermal Efficiency: 0.78-0.84 (78-84%) * Tank Insulation: Minimum R-12 * Recovery Capacity: 40-60 gallons per hour at 70°F temperature rise * Standby Loss: 0.3-0.5% per hour of stored energy * Setpoint Temperature: 48.9°C (120°F) baseline **EnergyPlus Objects** Primary heating component: * `WaterHeater:Mixed` (Fuel Type: NaturalGas) * Thermal Efficiency: 0.80 * Heater Capacity: 12,000 W (40,000 Btu/hr) * Tank Volume: 0.1893 m³ (50 gallons) typical * Off-cycle parasitic loss: 0.5 W/K Supporting loop components: * `PlantLoop` (Service Water Heating Loop) * `Pump:ConstantSpeed` (circulation pump) * `SetpointManager:Scheduled` (temperature control) * `Connector:Splitter` and `Connector:Mixer` * `Pipe:Adiabatic` (supply and return piping) Demand-side components: * `WaterUse:Connections` (fixture groupings) * `WaterUse:Equipment` (individual fixtures) Control and scheduling: * `Schedule:Constant` (setpoint temperature) * `Schedule:Compact` (demand profile) * `ScheduleTypeLimits` (range definitions) * `PlantEquipmentOperationSchemes` * `PlantEquipmentOperation:HeatingLoad` **Application** **Building Types (19 total):** * Automotive facilities * Dining/food service (all types) * Dormitories and residential facilities * Exercise and recreation centers * Fire stations * Grocery stores * Hospitals and medical centers * Hotels and motels * Manufacturing facilities * Penitentiaries * Performing arts facilities * Schools and universities * Sports arenas * All other unlisted building types **Selection Criteria:** * High to moderate hot water demand * Occupancy with sustained use patterns * Food service operations * 24/7 institutional operations * Cost optimization with natural gas availability **Design Parameters** **Tank Sizing:** ``` Tank Volume = (Peak Hour Demand × Temperature Rise) / (Recovery Rate × Time) Example: 200 gpm demand, 70°F rise, 50 gpm recovery, 1 hour target Volume = (200 × 70) / (50 × 60) = 46 gallons → Select 50-75 gallon tank ``` **Element Power:** ``` Heater Capacity = (Tank Volume × Temperature Rise) / Recovery Time × 0.001163 Example: 50 gallon tank, 70°F rise, 1 hour recovery Capacity = (50 × 70) / 1 × 0.001163 = 4.07 kW ≈ 12-15 kW gas input (Gas heater has lower efficiency than electrical energy conversion) ``` **Recovery Performance:** ``` Recovery Time (hours) = (Tank Volume × Temperature Rise) / (Input Capacity × Efficiency) Example: 50 gal, 70°F rise, 40,000 Btu/hr input, 0.80 efficiency Recovery = (50 × 70) / (40,000 × 0.80 / 3,412) = ~90 minutes ``` **Energy Consumption** ``` Annual Energy = [Daily Volume (gal) × Days/Year × Temperature Rise (°F) × 8.33 lb/gal × 1 Btu/lb°F + Annual Standby Loss] / Efficiency Standby Loss = Tank Surface Area × U-value × (Setpoint - Ambient) × Hours/Year Example: 20 gal/day, 365 days, 70°F rise Energy = [20 × 365 × 70 × 8.33 / 0.80] + Standby = 4.7 Therms energy use + ~2 Therms standby = 6.7 Therms per year (~$10 at $1.50/therm) ``` ### System B: Electric Resistance Storage Water Heater **Component Configuration** **Primary Heating Component:** * Storage Tank: Insulated steel tank (40-50 gallons typical) * Heating Element: One or two electric resistance elements * Upper element: 2-5 kW (primary heating) * Lower element: 2-5 kW (backup or simultaneous heating) * Thermostat: Dual setpoint with element sequencing * Safety Relief: Pressure and temperature relief valve **Distribution System:** * Circulation Pump: Optional (demand-based or timed circulation) * Supply Piping: Insulated copper or PEX (minimum R-3.5 insulation) * Return Piping: Optional circulation return or drain connection * Expansion Tank: Accommodates thermal expansion (10% of tank volume) * Check Valve: Prevents backflow from building to supply **Electrical System:** * Single Circuit: 240V, 20 A breaker, #12 AWG wire (single element) * Dual Circuit: Two 20 A breakers or 40 A main (dual elements) * Disconnect Switch: Manual disconnect within sight of heater **Performance Characteristics:** * Thermal Efficiency: 1.0 (100% - all electrical energy heats water) * Tank Insulation: Minimum R-12 * Recovery Capacity: 20-40 gallons per hour at 70°F temperature rise * Standby Loss: 0.3-0.5% per hour of stored energy * Setpoint Temperature: 48.9°C (120°F) baseline **EnergyPlus Objects** Primary heating component: * `WaterHeater:Mixed` (Fuel Type: Electricity) * Thermal Efficiency: 1.0 * Heater Capacity: 4,500 W (single element) typical * Tank Volume: 0.1893 m³ (50 gallons) typical * Off-cycle parasitic loss: 0.5 W/K Supporting loop components: * `PlantLoop` (Service Water Heating Loop) * `Pump:ConstantSpeed` (circulation pump) * `SetpointManager:Scheduled` (temperature control) * `Connector:Splitter` and `Connector:Mixer` * `Pipe:Adiabatic` (supply and return piping) Demand-side components: * `WaterUse:Connections` (fixture groupings) * `WaterUse:Equipment` (individual fixtures) Control and scheduling: * `Schedule:Constant` (setpoint temperature) * `Schedule:Compact` (demand profile) * `ScheduleTypeLimits` (range definitions) * `PlantEquipmentOperationSchemes` * `PlantEquipmentOperation:HeatingLoad` **Application** **Building Types (17 total):** * Convenience stores * Convention centers * Courthouses * Health-care clinics * Libraries * Motion picture theaters * Museums * Office buildings * Parking garages * Police stations * Post offices * Religious facilities * Retail stores * Town halls * Transportation facilities * Warehouses * Workshops **Selection Criteria:** * Low to minimal hot water demand * Public/government buildings with infrequent use * Compact spaces with limited piping * Buildings without commercial food service * Adequate electrical service available **Design Parameters** **Tank Sizing:** ``` Tank Volume = (Peak Hour Demand × Temperature Rise) / (Recovery Rate × Time) Example: 50 gpm demand, 70°F rise, 30 gpm recovery, 1 hour target Volume = (50 × 70) / (30 × 60) = 82 gallons → Select 75-100 gallon tank ``` **Element Power:** ``` Element Power (kW) = (Tank Volume in gal × Temperature Rise in °F) / (Recovery Time in hr × 3.412 Btu/kWh) Example: 50 gallon tank, 70°F rise, 1.5 hour recovery Power = (50 × 70) / (1.5 × 3.412) = 6.8 kW Select 4.5 kW for standard installation (90-120 min recovery) ``` **Recovery Performance:** ``` Recovery Time (hours) = (Tank Volume × Temperature Rise) / (Element Power × 3.412) Example: 50 gal, 70°F rise, 4.5 kW element Recovery = (50 × 70) / (4.5 × 3.412) = 2.27 hours ≈ 135 minutes ``` **Energy Consumption** ``` Annual Energy = [Daily Volume (gal) × Days/Year × Temperature Rise (°F) × 8.33 lb/gal × 1 Btu/lb°F / 3,412 Btu/kWh] + Annual Standby Loss Standby Loss = Tank Surface Area × U-value × (Setpoint - Ambient) × Hours/Year Example: 20 gal/day, 365 days, 70°F rise Energy = [20 × 365 × 70 × 8.33 / 3,412] + Standby = 1.25 MWh energy use + ~0.3 MWh standby = 1.55 MWh per year (~$186 at $0.12/kWh) ``` ## System Selection Decision Process ### Step 1: Identify Building Area Type Match the proposed building to one of 36 listed building area types from Table G3.1.1-2. ### Step 2: Determine Baseline Heating Method **If building area type matches one of 19 System A types:** → **Baseline: Gas Storage Water Heater** **If building area type matches one of 17 System B types:** → **Baseline: Electric Resistance Storage Water Heater** **If building area type is not listed:** → **Baseline: Gas Storage Water Heater** (default "All others" category) ### Step 3: Apply Baseline System Specifications Use corresponding system's: * Fuel type (Natural Gas or Electricity) * Thermal efficiency (0.80 or 1.0) * Heater capacity * Tank volume based on building occupancy and use profile * Temperature setpoint and deadband ### Step 4: Model Baseline System Build complete EnergyPlus model including: * PlantLoop with pump and controls * WaterHeater:Mixed with assigned fuel type and efficiency * Demand-side equipment (fixtures) matching proposed building * All piping, expansion, and relief components * Schedules for hot water demand profile ### Step 5: Compare Proposed vs. Baseline * Calculate annual energy consumption for both systems * Compare on: Fuel type, system efficiency, hot water availability * Demonstrate proposed system performs at or better than baseline ## System Selection Decision Tree ``` START: Building Area Type Classification STEP 1: Match to Table G3.1.1-2 Categories RESIDENTIAL/LODGING FACILITIES ├─ Dormitory, Hotel, Motel, Multifamily, Penitentiary │ → System A (Gas Storage Water Heater) │ └─ Other residential-type buildings not listed → System A (default: Gas Storage) FOOD SERVICE OPERATIONS ├─ Dining (Bar lounge, Cafeteria, Family, Fast food) ├─ Grocery store └─ School/university (with cafeteria) → System A (Gas Storage Water Heater) RECREATIONAL FACILITIES ├─ Exercise center, Gymnasium, Sports arena └─ Performing arts theater → System A (Gas Storage Water Heater) INSTITUTIONAL/MEDICAL FACILITIES ├─ Hospital and outpatient surgery center ├─ Fire station, Manufacturing facility │ → System A (Gas Storage Water Heater) │ ├─ Health-care clinic, Library, Museum ├─ Police station, Courthouse, Town hall ├─ Religious facility, Post office │ → System B (Electric Resistance Water Heater) COMMERCIAL/OFFICE BUILDINGS ├─ Office → System B (Electric Resistance) ├─ Retail → System B (Electric Resistance) ├─ Convenience store → System B (Electric Resistance) └─ Automotive facility → System A (Gas Storage) SPECIALIZED/STORAGE FACILITIES ├─ Parking garage → System B (Electric Resistance) ├─ Warehouse → System B (Electric Resistance) ├─ Workshop → System B (Electric Resistance) ├─ Convention center → System B (Electric Resistance) ├─ Motion picture theater → System B (Electric Resistance) └─ Transportation facility → System B (Electric Resistance) UNLISTED BUILDING TYPES └─ All others → System A (Gas Storage Water Heater) [DEFAULT] END: Apply selected system to baseline model ``` ## Component Specifications by System ### Water Heater Tank Specifications | Parameter | Gas Storage | Electric Storage | | ---------------------- | ------------------------------ | ------------------------------ | | **Tank Material** | Carbon steel with glass lining | Carbon steel with glass lining | | **Tank Volume** | 50-100 gallons (190-380 L) | 40-50 gallons (150-190 L) | | **Insulation** | Minimum R-12 wrap | Minimum R-12 wrap | | **Pressure Rating** | 150 psi (1,034 kPa) | 150 psi (1,034 kPa) | | **Anode Rod** | Sacrificial magnesium | Sacrificial magnesium | | **Typical Weight** | 100-150 lbs empty | 80-120 lbs empty | | **Operating Pressure** | 75 psi relief valve | 75 psi relief valve | ### Heating Element Specifications | Parameter | Gas Storage | Electric Storage | | --------------------- | -------------------------------- | ----------------------------------------- | | **Primary Element** | Gas burner, combustion chamber | Electric resistance element (2-5 kW) | | **Backup Element** | Not applicable | Second electric element (2-5 kW) optional | | **Burner Efficiency** | 0.78-0.84 (78-84%) | 1.0 (100%) | | **Capacity** | 40,000 Btu/hr (12 kW input) | 4,500 W (15,000 Btu/hr) single | | **Burner Type** | Natural gas pilot light ignition | Immersion electric element | | **Combustion Air** | Required (flue vent) | Not required | | **Venting** | Vent to exterior via flue | No venting required | ### Circulation Pump Specifications | Parameter | Specification | | --------------------- | --------------------------------------------- | | **Pump Type** | Constant speed centrifugal pump | | **Design Flow Rate** | 3-5 gpm typical | | **Design Head** | 100,000-300,000 Pa (1-3 psi) | | **Motor Efficiency** | 0.85 (85%) minimum | | **Control Type** | Intermittent (on demand) or timed circulation | | **Power Consumption** | 0.25-0.5 kW continuous run | ### Distribution Piping Specifications | Parameter | Specification | | ------------------------------------ | ------------------------------------------ | | **Material** | Copper (preferred), PEX, CPVC | | **Supply Line Diameter** | 1/2" to 1" (12-25 mm) | | **Return Line Diameter** | 1/2" to 3/4" (12-19 mm) | | **Insulation** | Minimum R-3.5 (0.62 m²K/W) | | **Insulation Thickness** | Minimum 1.5" (38 mm) | | **Max Line Length (no circulation)** | 30 feet (9 m) | | **Support Spacing** | Every 4-6 feet horizontal; 8 feet vertical | ### Expansion Tank Specifications | Parameter | Specification | | ------------------------- | -------------------------------------- | | **Volume** | 10% of water heater tank volume | | **Example (50 gal tank)** | 5-gallon expansion tank | | **Precharge Pressure** | 75 psi (75% of static pressure) | | **Type** | Air bladder (replaceable preferred) | | **Installation** | Saddle valve on cold water supply line | ### Relief Valve Specifications | Parameter | Specification | | ----------------------- | ------------------------------- | | **Pressure Setting** | 75 psi (517 kPa) | | **Temperature Setting** | 210°F (99°C) | | **Connection Size** | 3/4" NPT | | **Installation** | Vertical on tank side | | **Discharge** | To drain (visible termination) | | **Material** | Brass body, stainless internals | ## EnergyPlus Simulation Inputs ### Plant Loop Configuration ``` PlantLoop (Service Water Heating Loop) ├─ Loop Temperature Setpoint Node: SWH Supply Outlet Node ├─ Maximum Loop Temperature: 100°C ├─ Minimum Loop Temperature: 10°C ├─ Design Flow Rate: Autosize (based on demand) ├─ Plant Loop Volume: Autosize │ ├─ SUPPLY SIDE │ ├─ Pump:ConstantSpeed │ ├─ Connector:Splitter │ ├─ Branch (WaterHeater:Mixed) │ ├─ Connector:Mixer │ └─ Pipe:Adiabatic (outlet) │ └─ DEMAND SIDE ├─ Connector:Splitter ├─ Branch (WaterUse:Connections) ├─ Connector:Mixer └─ Pipe:Adiabatic (return) ``` ### Water Heater Object Configuration **For System A (Gas Storage):** ``` WaterHeater:Mixed ├─ Name: Gas Storage Water Heater ├─ Tank Volume: 0.1893 m³ (50 gallons) ├─ Setpoint Temperature: 48.9°C (120°F) ├─ Deadband: 2.0°C (3.6°F) ├─ Maximum Temperature: 70°C (158°F) ├─ Heater Control Type: Cycle ├─ Heater Maximum Capacity: 12,000 W ├─ Heater Fuel Type: NaturalGas ├─ Heater Thermal Efficiency: 0.80 ├─ Off Cycle Parasitic Capacity: 0.5 W/K └─ Off Cycle Parasitic Energy Factor: 1.0 ``` **For System B (Electric Resistance):** ``` WaterHeater:Mixed ├─ Name: Electric Storage Water Heater ├─ Tank Volume: 0.1893 m³ (50 gallons) ├─ Setpoint Temperature: 48.9°C (120°F) ├─ Deadband: 2.0°C (3.6°F) ├─ Maximum Temperature: 70°C (158°F) ├─ Heater Control Type: Cycle ├─ Heater Maximum Capacity: 4,500 W ├─ Heater Fuel Type: Electricity ├─ Heater Thermal Efficiency: 1.0 ├─ Off Cycle Parasitic Capacity: 0.5 W/K └─ Off Cycle Parasitic Energy Factor: 1.0 ``` ### Demand-Side Configuration ``` WaterUse:Connections ├─ Name: Fixture Group (Bathrooms, Kitchen, etc.) ├─ Inlet Node: Hot Water Supply from Heater ├─ Outlet Node: Return to Drain ├─ Number of Equipment: 1 or more │ └─ WaterUse:Equipment (per fixture) ├─ Name: Specific Fixture (Sink, Shower, etc.) ├─ End-Use Subcategory: Restroom, Kitchen, etc. ├─ Peak Flow Rate: m³/s (varies by fixture) ├─ Flow Rate Fraction Schedule: Time-dependent usage └─ Hot Water Supply Temperature Schedule: 48.9°C baseline ``` ### Typical Peak Flow Rates | Fixture Type | Peak Flow Rate | End-Use | | ------------- | ------------------------ | ----------------- | | Bathroom sink | 0.000076 m³/s (0.12 gpm) | Restroom | | Kitchen sink | 0.000189 m³/s (0.30 gpm) | Kitchen | | Shower | 0.00315 m³/s (2.0 gpm) | Restroom | | Mop sink | 0.000632 m³/s (1.0 gpm) | Cleaning | | Dishwasher | 0.00315 m³/s (2.0 gpm) | Kitchen equipment | ## Key Controls and Setpoints ### Baseline Temperature Setpoints **Hot Water Setpoint (Supply):** * Baseline: 48.9°C (120°F) * Minimum (code): 43.3°C (110°F) * Maximum (safety): 60°C (140°F) * Deadband: 2.0°C minimum between on/off **Optional Setback:** * Reduced setpoint during unoccupied hours: 43.3°C (110°F) * Reduces standby loss without scalding risk ### Peak Hot Water Demand Schedule **Typical Office Building:** ``` Midnight - 6 AM: 0% demand (closed) 6 AM - 8 AM: 10% demand (morning arrival) 8 AM - 12 PM: 20% demand (peak morning use) 12 PM - 1 PM: 30% demand (lunch period, if applicable) 1 PM - 5 PM: 10% demand (afternoon occasional use) 5 PM - 6 PM: 15% demand (afternoon departure) 6 PM - Midnight: 0% demand (closed) ``` **Typical Residential Building:** ``` Midnight - 6 AM: 5% demand (minimal) 6 AM - 8 AM: 40% demand (morning showers/baths) 8 AM - 12 PM: 15% demand (light use) 12 PM - 5 PM: 10% demand (occasional use) 5 PM - 8 PM: 25% demand (dinner, evening) 8 PM - 10 PM: 20% demand (evening showers/baths) 10 PM - Midnight: 10% demand (light use) ``` **Typical Dining/Food Service:** ``` Midnight - 6 AM: 5% demand (prep) 6 AM - 10 AM: 20% demand (breakfast) 10 AM - 12 PM: 10% demand (between meals) 12 PM - 2 PM: 50% demand (lunch peak) 2 PM - 5 PM: 15% demand (between service) 5 PM - 8 PM: 60% demand (dinner peak) 8 PM - Midnight: 10% demand (cleanup) ``` ### Circulation Pump Operation **Continuous Circulation:** * Operates continuously during occupied hours * Maintains hot water availability at all fixtures * Increases operating cost * Reduces water wait time **Timed/Demand-Based Circulation:** * Operates on schedule (e.g., morning 6-9 AM, evening 4-7 PM) * Timer-controlled during peak demand periods * Reduces standby loss outside peak periods * Recommended for energy efficiency ### Outdoor Air Damper (if applicable) **Cold Climate Freeze Protection (CZ 3B-8):** * System 7+ with outdoor air intake must have freeze protection * Damper minimum position to prevent freezing * Not typically required for SWH systems (indoor location) ### System Operation Availability **Schedule Status:** * Available: 1.0 (system always ready to operate) * Unavailable: 0.0 (system disabled - rarely used for SWH) **Typical SWH System:** * Always available (Schedule:Constant = 1.0) * Hot water demand varies by occupancy schedule * System responds to thermostat and demand-side loads ## Baseline Model Compliance Demonstration ### Proposed vs. Baseline Comparison **Energy Consumption:** * Calculate annual fuel/electricity for proposed system * Calculate annual fuel/electricity for baseline system * Compare kWh (electric) or Therms (gas) per year **Efficiency:** * Proposed system efficiency ≥ Baseline system efficiency * Or offset higher demand with improved HVAC efficiency **Hot Water Availability:** * Proposed system provides adequate hot water for building occupancy * Baseline establishes minimum acceptable performance **Example Compliance Path:** A 10,000 sf office building proposes electric resistance water heater (System B). ``` Baseline (per Table G3.1.1-2): Electric resistance storage (Method B) Proposed: Instantaneous electric water heater (higher efficiency) Baseline Energy: - 50-gal tank storage + standby loss - Annual: 1,500 kWh estimated Proposed Energy: - Instantaneous (no storage, minimal standby loss) - Annual: 1,000 kWh estimated Compliance: Proposed meets or exceeds baseline requirement ✓ ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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