Hoare Lea Infiltration ACH Tool v3.1

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Project

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Project name

Project no.

Prepared by

Client / building

Date

Location / EPW

M

Method & Operation Mode

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Calculation method

Method A calculates whole-building normal-pressure ACH via pressure-network solver.

Operation mode

🎯

Single point

One wind speed, direction & temperature

📅

EPW year profile

8 760-hour annual simulation

Upload EPW weather file Uses dry-bulb temperature, wind direction and wind speed from the EPW. Indoor temp assumption (°C)

Terrain category — wind profile correction

Met station ref height (m)

Building effective height (m)

Wind correction: ×1.093 (terrain) × 0.7 (shield) = ×0.765 applied to input wind speed. Façade shielding factor Effective shielding reduces wind pressure by 30%.

1

Building Airtightness

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q50 (m³/h.m² @ 50 Pa)

Exponent n

Volume V (m³)

Air density ρ (kg/m³)

Envelope area Aenv (m²) Conditioned floor area (m²) Core setpoint T_core (°C) — for exfiltration bar Required for the Heat Loss tab. The chart is now normalised only and displays W/m² and kWh/m² rather than absolute kW and kWh. Q50 = q50 × Aenv. Façade rows share this leakage by area or override %. Heating degree-days HDD (°C·day/yr) Used for annual heat-loss penalty estimate. Default: London ~2462 HDD.

Hoare Lea Plant Sizing ACH (h⁻¹) ⚠ Default 0.1 h⁻¹ is a conservative value. Always check and confirm the infiltration ACH from the Hoare Lea Plant Sizing document for this project before finalising. Shown as an amber line on all charts and compared against CIBSE and PHPP benchmarks.

Benchmark / guide reference

CIBSE Guide A air-permeability divisor benchmark

Subtype / table group

Table row / size / form

CIBSE Guide A benchmark will be populated on load.

CIBSE benchmark method

CIBSE table statistic

Preferred method: table lookup/interpolation. If q50 is between published rows, peak/average ACH is linearly interpolated from the table. Divisor mode remains available as a transparent check. The dropdown shows the intended table-row description where available. Use Custom ACH for other guides, contractor-submitted ACH values, or ER values. Ventilation system interaction Used only for the CIBSE q50/divisor benchmark comparison. The pressure-network ACH result is not reduced.

CIBSE basis: wind pressure uses Pw = 0.5 × ρ × Cp × V². Cp is calculated automatically from façade orientation and wind direction using the V1 CIBSE directional interpolation model. Stack signs follow the convention that winter buoyancy drives inflow at lower openings and outflow at higher openings.

IESVE recommended statistic

2

Façade Leakage Paths

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WDR column: ☑ ticked = Wind-Driven Rain +15% ON · ☐ unticked = no correction Cp calculated automatically from orientation vs wind direction — no manual input needed

Name	Orient °N	Area m²	Height z (m)	Share % (optional)	WDR

3

Additional Pressure Paths

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What are additional pressure paths?
These are openings in the building envelope that are separate from the general façade leakage already captured by q50 — such as chimneys, extract grilles, open vents, duct leakage, and service shafts.
Where do I get the values? From mechanical drawings (duct sizes, grille areas, flow rates), commissioning reports (extract/supply flow rates), or building services specifications. Leave this section empty if no additional deliberate openings exist.

🔥Chimney

What type of opening?Flow rate from flue gas calculation or heating engineer specification. Height = top of flue above ground.

Flow rate (m³/s)converted to m³/h internallyl/s ÷ 1000 = m³/s; tool multiplies by 3600 for m³/h balance. e.g. 50 l/s = 0.050 m³/s = 180 m³/h

Height above ground (m)from drawings

Air direction

← Out of building (extract, exhaust, flue)→ Into building (supply, make-up air)

Does wind affect this opening?

🚫 No wind effect

Terminal is sheltered, internal, or behind a louvred screen. Wind does not drive or resist flow. Examples: internal shaft, sealed duct, grille behind plant room.

💨 Slight wind suction (leeward or side face)

Terminal on a leeward or side wall — wind creates mild suction that slightly helps extract flow. Typical for wall-mounted flue terminals and side-wall grilles.

↑ Roof terminal — stronger suction

Terminal on the roof — wind creates stronger suction that significantly helps extract flow. Typical for roof cowls, roof extract fans, and high-level flues.

ℹ️ Only add paths that were sealed during the airtightness test and are therefore not already captured in q50.

B

Method B — Zone Allocation

        ✅
        Method A done
      

→

        ②
        Upload zone CSV
      

→

        ③
        Run Method B
      

Method B will allocate: Mean ACH.

Upload IESVE zone CSV Upload the IESVE General Template CSV export directly — all columns auto-detected, any number of zones.
Required: Space Name (Real) · Volume (m³) (Real) · Facade Area (m²) (Real)
Output CSV = your full IESVE template (all original columns) + 8 appended HL columns:
HL Zone Classification · HL Facade Allocation Factor · HL Infiltration ACH (h-1) · HL Infiltration Flow (m3/h) · HL Volume Source · HL Building Volume Used · HL Whole-Building ACH Used · HL IESVE Statistic
Facade Area > 0 → perimeter (allocated). Facade = 0 → core (zero). Sub Type = Void → excluded entirely. Use total building volume from uploaded CSV (overrides manual entry)

      Complete steps ① and ② above, then press Run Method B.
    

4

Calculate

Calculation complete. Height spread 0.0 m — add multi-height paths to activate stack ACH.