Utility Balance Screening

Use this skill for public, educational utility-system screening. It estimates instrument air demand, cooling water flow from a duty and a cooling-water temperature rise, a fuel gas Wobbe index with a band check, and a simple capacity utilisation roll-up so an agent can scope a utility study before detailed design.

When to Use

• When a user asks how much instrument air a set of consumers needs or whether the air/cooling supply is large enough.
• When an agent needs a quick cooling-water flow estimate from a heat duty and a permitted temperature rise.
• When a fuel gas Wobbe index must be screened against a sales/fuel band without confidential gas data.
• When examples must run without proprietary utility loads, vendor data, or company specs.

Inputs

• instrument_air_consumers: number of instrument air consumers (integer count).
• air_per_consumer_nm3_h: average free-air demand per consumer in Nm3/h, default 0.3.
• cooling_duty_kw: total cooling duty to reject in kW, default 0.
• cooling_water_delta_t_c: permitted cooling-water temperature rise in degrees C, default 10.
• fuel_gas_lhv_mj_sm3: optional fuel gas lower heating value in MJ/Sm3.
• fuel_gas_relative_density: optional fuel gas relative density (air = 1).
• wobbe_min: lower Wobbe index band in MJ/Sm3, default 47.2.
• wobbe_max: upper Wobbe index band in MJ/Sm3, default 51.41.
• instrument_air_capacity_nm3_h: optional installed instrument air capacity in Nm3/h.
• cooling_water_capacity_m3_h: optional installed cooling water capacity in m3/h.

Outputs

• instrument_air_demand_nm3_h: consumer count multiplied by per-consumer demand and a design margin.
• cooling_water_flow_m3_h: cooling water flow from the duty and the temperature rise.
• wobbe_index_mj_sm3: fuel gas Wobbe index, or null if no fuel gas data is supplied.
• wobbe_in_band: True/False if a Wobbe index is computed, otherwise null.
• air_utilisation: demand divided by installed air capacity, or null.
• cooling_utilisation: flow divided by installed cooling capacity, or null.
• utility_warning: ok, watch, air-undersized, or cooling-undersized.
• wobbe_warning: ok, wobbe-out-of-range, or no-fuel-data.
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class UtilityBalanceModel uses open utility relations only:

• instrument air demand uses Q_air = N * q_consumer * margin with a 1.3 design margin.
• cooling water flow uses Q_cw = duty * 3600 / (rho * cp * dT) with rho = 1000 kg/m3 and cp = 4.18 kJ/kg.K, giving m3/h.
• the Wobbe index uses W = LHV / sqrt(relative_density) and is flagged inside or outside [wobbe_min, wobbe_max].
• capacity utilisation uses demand / capacity for air and cooling when a capacity is supplied.

This is educational and screening-only logic. It assumes incompressible cooling water with constant properties, a fixed air design margin, and a single fuel gas Wobbe band. It is not a replacement for validated utility-system balances or qualified utility design.

Python Usage Pattern

from utility_balance_screening import UtilityBalanceModel

model = UtilityBalanceModel()
result = model.evaluate(
    instrument_air_consumers=120,
    cooling_duty_kw=2500.0,
    cooling_water_delta_t_c=10.0,
    fuel_gas_lhv_mj_sm3=39.0,
    fuel_gas_relative_density=0.62,
    instrument_air_capacity_nm3_h=60.0,
    cooling_water_capacity_m3_h=250.0,
)

print(result.instrument_air_demand_nm3_h)
print(result.cooling_water_flow_m3_h)
print(result.wobbe_index_mj_sm3)
print(result.utility_warning)

Related NeqSim Functionality

For validated utility specification and balances, redirect to NeqSim resources:

• the neqsim-utilities-specification skill — steam levels, cooling water, instrument air, fuel gas, and nitrogen specification guidance.
• neqsim.standards.gasquality.Standard_ISO6976 — validated calorific value and Wobbe index per ISO 6976.
• proposed enterprise-utility-systems-review — consolidated utility duty roll-up and capacity check; candidate enterprise extension.

This skill is a public triage layer that decides when to invoke a validated utility balance.

Validation Checklist

• Consumer count is a non-negative integer and per-consumer demand is positive.
• Cooling duty is non-negative and the cooling-water temperature rise is positive.
• Fuel gas LHV and relative density are supplied together or not at all.
• Tests cover air demand, cooling flow, a Wobbe band check, capacity utilisation, and invalid input.
• Real utility design is redirected to validated NeqSim resources and qualified review.

Common Mistakes

Limitations

• No proprietary utility loads, vendor data, or company specifications are included.
• Cooling water uses constant incompressible-water properties; no fouling or approach is modelled.
• A single Wobbe band is used; no full ISO 6976 composition calculation is performed.

References

• NORSOK U-001, Subsea production systems / utility system requirements.
• ISA-7.0.01, Quality Standard for Instrument Air.
• ISO 6976, Natural gas — Calculation of calorific values, density, relative density and Wobbe indices.
• NeqSim repository: https://github.com/equinor/neqsim