MCS Heat Pump Calculator - Python Implementation

A Python implementation of the MCS (Microgeneration Certification Scheme) Heat Pump Calculator for heat loss calculations and heat pump system design, based on BS EN 12831.

Features

• Heat Loss Calculation: Room-by-room and whole building heat loss calculations following BS EN 12831
• Inter-Room Heat Transfer: Model heat loss/gain between adjacent rooms at different temperatures (compatible with heatlossjs)
• Degree Days Data: Built-in CIBSE degree days data for all UK postcode areas
• Hot Water Energy: Calculate domestic hot water energy requirements
• Heat Pump Sizing: Size heat pumps based on design heat loss and hot water demand
• Radiator Sizing: Calculate radiator sizing for low-temperature heat pump systems
• Annual Energy Consumption: Estimate annual energy consumption and costs
• U-Value Calculations: Floor U-value calculations for solid and suspended floors
• Flexible Modeling: Choose between MCS-style (independent rooms) or detailed inter-room thermal modeling

Installation

Using Conda (Recommended)

# Clone the repository
git clone <repository-url>
cd python_mcs_heatloss

# Create and activate conda environment
conda create -n python_mcs_heatloss python=3.12
conda activate python_mcs_heatloss

# Install dependencies
pip install -r requirements.txt

# Run tests
pytest tests/test_calculator.py -v

# Run example
python example_usage.py

Using pip

pip install -r requirements.txt

Quick Start

from mcs_calculator import HeatPumpCalculator
from mcs_calculator import Wall, Window, Floor

# Initialize calculator for Manchester (M postcode)
calc = HeatPumpCalculator(postcode_area='M', building_category='B')

# Create building
building = calc.create_building('My House')

# Create a room
living_room = calc.create_room(
    name='Living Room',
    room_type='Lounge',
    floor_area=25.0,
    height=2.4
)

# Add fabric elements
living_room.walls.append(Wall('External Wall', area=15, u_value=0.3))
living_room.windows.append(Window('Window', area=4, u_value=1.4))
living_room.floors.append(Floor('Ground Floor', area=25, u_value=0.25))
living_room.thermal_bridging_factor = 0.15

building.add_room(living_room)

# Calculate heat loss
summary = calc.calculate_building_heat_loss()

print(f"Total Heat Loss: {summary['total_heat_loss']['watts']:.0f} W")
print(f"Annual Energy: {summary['total_heat_loss']['kwh']:.0f} kWh")

Module Structure

mcs_calculator/
├── __init__.py          # Package initialization
├── calculator.py        # Main HeatPumpCalculator class
├── room.py             # Room, Building, Wall, Window, Floor classes
└── data_tables.py      # Lookup tables (degree days, U-values, etc.)

tests/
└── test_calculator.py   # Comprehensive test suite

example_usage.py         # Complete example with detailed output

Core Classes

HeatPumpCalculator

Main calculator class for heat pump system design.

calc = HeatPumpCalculator(postcode_area='SW', building_category='B')

# Get location information
location = calc.get_location_info()

# Create building and rooms
building = calc.create_building('House Name')
room = calc.create_room('Living Room', 'Lounge', floor_area=25)

# Calculate heat loss
summary = calc.calculate_building_heat_loss()

# Hot water energy
hw_energy = calc.calculate_hot_water_energy(num_occupants=4)

# Size heat pump
sizing = calc.size_heat_pump(design_heat_loss_kw=5.0, hot_water_demand_kw=3.0)

# Annual energy consumption
energy = calc.calculate_annual_energy_consumption(
    space_heating_kwh=10000,
    hot_water_kwh=4000,
    cop=3.5
)

# Radiator sizing
rad_sizing = calc.calculate_radiator_sizing(
    room_heat_loss_w=1500,
    room_temp=21,
    flow_temp=45,
    return_temp=40
)

Room

Represents a room with fabric elements and calculates heat loss.

from mcs_calculator import Room, Wall, Window, Floor

room = Room(
    name='Bedroom',
    room_type='Bedroom',
    design_temp=18,
    volume=36,
    air_change_rate=1.0,
    thermal_bridging_factor=0.15
)

# Add fabric elements
# External walls
room.walls.append(Wall('External Wall', area=12, u_value=0.3, boundary='external'))

# Party wall to adjacent room (for inter-room heat transfer)
room.walls.append(Wall('Party Wall to Hall', area=8, u_value=0.5, boundary='hall'))

# Unheated space
room.walls.append(Wall('Loft', area=15, u_value=0.2, boundary='unheated', boundary_temp=18))

room.windows.append(Window('Window', area=2, u_value=1.4))
room.floors.append(Floor('Floor', area=15, u_value=0.25, temperature_factor=0.5))

# Calculate heat loss
external_temp = -2.0
degree_days = 2033

# Without inter-room heat transfer
fabric_loss = room.fabric_heat_loss_watts(external_temp)

# With inter-room heat transfer (provide room temperatures)
room_temps = {'hall': 19, 'kitchen': 18}
fabric_loss_with_interroom = room.fabric_heat_loss_watts(external_temp, room_temps)

vent_loss = room.ventilation_heat_loss_watts(external_temp)
total_loss = room.total_heat_loss_watts(external_temp, room_temps)
annual_kwh = room.total_heat_loss_kwh(external_temp, degree_days)

Wall Boundaries

Walls support different boundary types for flexible thermal modeling:

# External boundary (uses external temperature)
Wall('External Wall', area=10, u_value=0.3, boundary='external')

# Ground boundary (uses ground temperature)
Wall('Ground Contact', area=10, u_value=0.5, boundary='ground', boundary_temp=10.6)

# Unheated space (uses specified or default 18°C)
Wall('To Garage', area=8, u_value=0.4, boundary='unheated', boundary_temp=15)

# Adjacent room (uses room's design temperature for inter-room heat transfer)
Wall('Party Wall', area=12, u_value=0.5, boundary='kitchen')

Data Tables

Built-in lookup tables for UK-specific data.

from mcs_calculator import DegreeDays, RoomTemperatures, VentilationRates, FloorUValues

# Degree days
degree_days = DegreeDays.get_degree_days('M')  # Manchester
design_temp = DegreeDays.get_design_temp('M')
location = DegreeDays.get_location('M')

# Room temperatures
temp = RoomTemperatures.get_temperature('Lounge')  # 21°C

# Ventilation rates
ach = VentilationRates.get_rate('Kitchen', category='B')  # 1.5 ACH

# Floor U-values
u_value = FloorUValues.calculate_floor_u_value(
    floor_type='solid',
    perimeter=20,
    area=25,
    insulation_thickness=0.1
)

Heat Loss Calculation Methodology

The calculator follows BS EN 12831 for heat loss calculations:

Fabric Heat Loss

Q_fabric = Σ (A × U × ΔT × f)

Where:

• A = area (m²)
• U = U-value (W/m²K)
• ΔT = temperature difference (K)
• f = temperature correction factor (e.g., 0.5 for ground floors)

Inter-Room Heat Transfer

For walls with adjacent room boundaries:

Q_inter_room = A × U × (T_room - T_adjacent)

This allows modeling heat loss/gain between rooms at different temperatures, providing more accurate thermal modeling for complex buildings.

Ventilation Heat Loss

Q_ventilation = 0.33 × n × V × ΔT

Where:

• 0.33 = specific heat capacity of air (Wh/m³K)
• n = air change rate (ACH)
• V = volume (m³)
• ΔT = temperature difference (K)

Thermal Bridging

Additional 15% (typical for post-2006 buildings) added to fabric heat loss to account for thermal bridges.

Annual Energy

kWh = Q × DD × 24 / 1000

Where:

• Q = heat loss per degree (W/K)
• DD = degree days
• 24 = hours per day

Room Types and Default Values

Room Type	Design Temp (°C)	Ventilation (ACH)
Lounge	21	1.0 (Category B)
Dining	21	1.0
Bedroom	18	1.0
Kitchen	18	1.5
Bathroom	22	1.5
Hall/Landing	18	1.0

Building Categories:

• Category A: Higher ventilation (older/leakier buildings)
• Category B: Medium ventilation (standard)
• Category C: Lower ventilation (very tight/new buildings)

Example Output

HEAT LOSS CALCULATION
================================================================================

Room                   Temp   Fabric W     Vent W    Total W   Annual kWh
--------------------------------------------------------------------------------
Living Room            21.0        460        477        937         2124
Kitchen/Dining         18.0        268        501        769         1990
Bedroom 1              18.0        201        251        451         1168
--------------------------------------------------------------------------------
TOTAL                                                   2969         7259

HEAT PUMP SIZING
Required Heat Pump Capacity: 5.97 kW

ANNUAL ENERGY CONSUMPTION (COP = 3.5)
  Space Heating Demand: 7,259 kWh/year
  Hot Water Demand: 4,245 kWh/year
  Total Heat Demand: 11,504 kWh/year
  Electricity Consumption: 3,287 kWh/year
  Estimated Annual Cost (@ £0.30/kWh): £986

Validation

This implementation has been validated against:

1. MCS Excel Calculator - Exact match (within 0.001W precision)
2. heatlossjs - 0.01% difference (0.12W out of 1179W on test case)

See VALIDATION_REPORT.md and HEATLOSSJS_COMPARISON.md for detailed validation results.

Test Results

✅ 61/61 tests passing (100%)

• Formula accuracy: 4/4 ✓
• Excel MCS validation: 16/16 ✓
• Cross-validation: 18/18 ✓
• Core functionality: 20/20 ✓
• heatlossjs validation: 7/7 ✓ (including inter-room heat transfer)

Testing

The package includes comprehensive tests:

# Run all tests
pytest tests/test_calculator.py -v

# Run specific test class
pytest tests/test_calculator.py::TestRoom -v

# Run with coverage
pytest tests/test_calculator.py --cov=mcs_calculator

Test coverage includes:

• Degree days lookup
• Floor U-value calculations
• Room heat loss (fabric and ventilation)
• Thermal bridging
• Hot water energy
• Heat pump sizing
• Radiator sizing
• Complete building calculations

Comparison with Excel Calculator

This Python implementation provides the same core functionality as the MCS Heat Pump Calculator Excel spreadsheet (Version 1.10), with the following advantages:

1. Programmatic Access: Integrate calculations into your own applications
2. Batch Processing: Calculate heat loss for multiple buildings efficiently
3. Version Control: Track changes to building designs over time
4. Automation: Automate repetitive calculations
5. Testing: Comprehensive test suite ensures accuracy
6. Extensibility: Easy to add custom calculations or modify existing ones

Requirements

• Python 3.12+
• openpyxl >= 3.1.2 (for reading Excel files)
• pandas >= 2.0.0
• numpy >= 1.24.0
• pytest >= 7.4.0 (for testing)

License

This is a Python implementation of publicly available MCS heat loss calculation methods following BS EN 12831.

Contributing

Contributions are welcome! Please ensure:

1. All tests pass: pytest tests/ -v
2. Code follows PEP 8 style guidelines
3. New features include tests
4. Documentation is updated

Support

For issues or questions, please open an issue on the GitHub repository.

References

• BS EN 12831-1:2017 - Energy performance of buildings - Method for calculation of the design heat load
• CIBSE Guide A - Environmental Design
• MCS Installation Standard MIS 3005
• MCS Heat Pump Calculator (Excel) Version 1.10

Version History

Version 1.0.0 (2025-10-06)

• Initial Python implementation
• Complete heat loss calculation engine
• Comprehensive test suite
• Example usage scripts
• Full documentation