Add demand calculation checks

[reyery]

Add guards for division by zero and checks for physical limitations.

[Copilot]

Pull Request Overview

This PR adds validation checks for division by zero and physical limitations in thermal network demand calculations. The changes prevent runtime errors and ensure physically valid configurations by validating temperature differences, pipe dimensions, and thermodynamic constraints before performing calculations.

Key Changes:

• Added validation for division by zero in temperature, flow rate, and heat transfer calculations
• Introduced new constants for minimum temperature differences and convergence tolerances
• Enhanced error messages to provide detailed diagnostic information

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
cea/constants.py	Adds new constants for minimum temperature differences and convergence tolerances
cea/technologies/thermal_network/thermal_network_loss.py	Adds division by zero check for pipe outlet temperature calculation
cea/technologies/thermal_network/thermal_network.py	Adds validation for Reynolds number, Darcy friction factor, and pipe dimension calculations
cea/technologies/thermal_network/substation_matrix.py	Adds validation for heat exchanger effectiveness iteration and temperature differences
cea/technologies/thermal_network/simplified_thermal_network.py	Adds validation for pipe diameter and thermal loss coefficient calculations
cea/technologies/substation.py	Adds temperature difference validation for heat capacity and heat exchanger calculations
cea/technologies/pumps.py	Adds validation for pump efficiency and water density constants
cea/technologies/heatpumps.py	Adds temperature validation for heat pump COP calculations across multiple heat pump types
cea/technologies/chiller_vapor_compression.py	Adds temperature validation and Carnot limit checks for chiller COP calculations
cea/demand/rc_model_SIA.py	Adds validation for building area and heat transfer coefficients in RC model
cea/demand/electrical_loads.py	Adds temperature difference validation for pump auxiliary energy calculations

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

The comment states 'Below 1 millikelvin' but the constant value is 0.001 K, which equals 1 millikelvin. The comment should say 'Below or equal to 1 millikelvin' or 'At 1 millikelvin or below' for accuracy.

Suggested change

	# Physical basis: Below 1 millikelvin, water flow becomes negligible and pump energy ≈ 0
	# Physical basis: At 1 millikelvin or below, water flow becomes negligible and pump energy ≈ 0

[Copilot]

The import statement is missing the numpy module which was removed from line 14 but is still used in the file (e.g., np.isclose at line 80). The numpy import should be retained.

Suggested change

	import pandas as pd
	import pandas as pd
	import numpy as np

[Copilot]

The comment references 'HEAT_EXCHANGER_EFFICIENCY_CONVERGENCE_TOL' but this constant is not imported or defined in this file or in constants.py. Either this constant should be imported and used instead of the hardcoded value, or the comment should be updated to remove the reference.

Suggested change

	tolerance = 1e-08 # Same as HEAT_EXCHANGER_EFFICIENCY_CONVERGENCE_TOL
	tolerance = 1e-08 # Convergence tolerance value

[Copilot]

[nitpick] The comment spans lines 756-757 but line 757 is not a continuation of the same logical statement needing a fix. The comment should be consolidated to a single line or properly structured as a multi-line comment block.

Suggested change

	# Check if primary side has meaningful temperature drop (thi != tho)
	# If temperatures are essentially equal, no heat transfer occurs, skip iteration
	# Check if primary side has meaningful temperature drop (thi != tho); if temperatures are essentially equal, no heat transfer occurs, skip iteration

[Copilot]

[nitpick] This multi-line comment (lines 786-788) describes validation logic but could be more concise. Consider consolidating to: 'Validate secondary side temperature rise from iteration results (unlike primary side input validation above).'

Suggested change

	# Check if secondary side has meaningful temperature rise (tci != tco)
	# Even if primary side had temperature drop, heat exchanger may produce negligible secondary-side change
	# This validates the RESULT of the iteration, while the check above validates the INPUT
	# Validate secondary side temperature rise from iteration results (unlike primary side input validation above).

[Copilot]

The comment on lines 879-880 describes handling zero cc_kWperK but the actual check on line 881 also checks for Q_heating_W == 0.0. The comment should mention both conditions being checked.

Suggested change

	# Handle case where cc_kWperK is zero (no heat capacity flow)
	# This can occur when temperature difference between supply and return is negligible
	# Handle cases where either cc_kWperK is zero (no heat capacity flow)
	# or Q_heating_W is zero (no heating load). This can occur when temperature difference between supply and return is negligible or there is no demand.