Field calcs for NZ HVAC/R techs

Metric calculators and BWOF inspection checklists for sizing, charging, testing, balancing and compliance. Works offline in the plant room.

Refrigeration

Air & sizing

Compliance (BWOF)

Hydronics

Electrical & units

Calculators are an aid for experienced technicians. Final selections must be checked against the NZ Building Code, the relevant AS/NZS standards and the manufacturer's data.

Saved jobs

Calcs you've saved on this phone, grouped by job number.

Forms

Commissioning sheets, certificates and test sheets. Each one saves as you go and produces a signed PDF.

Recent

Settings

Your details go on job notes and PDF reports. Everything stays on this phone.

Your business Company name

Technician Licence / cert no. IQP registration no. Phone Email

For forms and certificates

These fill in automatically on new commissioning sheets, CoCs, ESCs and test sheets.

Electrical registration / practising licence no. Employer licence no. Authentication mark

My signature

Sign once here. Forms then have a "Use my signature" button.

Add logo

Defaults

Gauge units Refrigerant Home town Appearance

Data

–

Feedback

Found a bug, a wrong answer, or have an idea? Send it straight to the developer.

Send feedback

About

DeltaCalc HVAC/R · Free beta

The calculators give rule-of-thumb answers to support site decisions by competent technicians. They don't replace a design, the NZ Building Code, AS/NZS standards or manufacturer instructions. Check results before relying on them.

Data sources

Winter design temperatures: Healthy Homes Standards Schedule 2, as listed in EECA's Good Practice Guide: Heat Pump Installation (2022).
Climate zones: H1/AS1 5th edition, Appendix C.
Refrigerant saturation data: calculated with CoolProp equations of state.
Summer design temperatures are estimates. Overwrite them with project data.

Job no.

Room sizer

Quick heat pump sizing with airflow, unit type and NZ code checks. Rule-of-thumb loads for quoting, not a full design.

Location Town / district

Summer design (°C, est.) Winter design (°C)

Winter is the Healthy Homes design temperature for the district. Summer is an estimate. Indoor design is 24°C cooling and 20°C heating. Overwrite with project data if you have it.

Room Room type

Length (m) Width (m) Ceiling (m)

Envelope

Insulation

Roof directly above Double glazed

Glazing & sun

Window area (m²) Main glass faces

External shading / blinds

Internal gains

Occupants Equipment (W)

Default set from room type. Server rooms: enter rack IT load.

Install site

Clear high wall Accessible ceiling void Low wall / under window Unit to bring in outdoor air

Refrigerant Pipe run (m)

Result

–

Recommended size–

Cooling load

–

Heating load

–

kW @ 3°C out

Load density

–

W/m²

Supply air

–

L/s

Air changes

–

per hour

Outdoor air

–

L/s min.

Standard nominal sizes (kW cooling) — selected size highlighted

Cooling load breakdown

Suggested unit type

Code & compliance checks

Rule-of-thumb sizing for site quoting. Design rates are typical values; verify against the current NZBC acceptable solutions, AS 1668.2, AS/NZS 5149 and the manufacturer's data before final selection. Larger commercial or healthcare spaces need a proper load calc.

Superheat & subcooling

Enter gauge pressures and line temperatures taken in cooling mode. Saturation temperatures come from built-in PT data. For blends it uses the dew point for superheat and the bubble point for subcooling.

System

Refrigerant Metering device

Gauge units

Suction (vapour) line

Suction pressure (kPa g) Suction line temp (°C)

Liquid line

Liquid pressure (kPa g) Liquid line temp (°C)

Targets & air temps

Target SH (K) Target SC (K) Outdoor air (°C)

Targets as a range, e.g. 4-8. Use the manufacturer's charging chart or service manual figures where you have them. Outdoor air is optional and is used for the condenser approach check.

Result

–

Superheat / subcooling (K)–

Evap sat (dew)

–

°C

Cond sat (bubble)

–

°C

Comp. ratio

–

abs / abs

Superheat against target

05101520 K

Subcooling against target

05101520 K

Diagnosis

Coil ΔT capacity check

Measure airflow and the air on and off the indoor coil to work out the capacity the unit is actually delivering, then compare it with the rated output.

Mode & airflow

Airflow (L/s) Rated capacity (kW)

For a high-wall split, take the airflow from the manufacturer's fan table at the fan speed it's running.

On-coil air

Air readings

Humidity reading

On-coil / return DB (°C) On-coil RH (%) Off-coil / supply DB (°C) Off-coil RH (%)

Read the return air at the filter and the supply air at the outlet, out of the airstream of any other unit. Let the unit run 15 minutes at a steady state first.

Result

–

Delivered capacity–

Air ΔT

–

Sensible

–

Latent

–

SHR

–

sensible / total

Condensate

–

L/h

Of rated

–

Against rated capacity

50%75%100%125%150%

The green band is 85–115%. Rated output is at standard test conditions, so field results normally sit somewhere in that band.

Checks

Nitrogen pressure test

Log a nitrogen pressure test over hours or days. Every check is corrected for temperature, so a cold morning doesn't look like a leak.

Pressure units

Your tests

Water flow

Flow from capacity and ΔT, or capacity from a measured flow. Corrects density and specific heat for glycol and temperature.

Result

–

Required flow–

Flow

–

L/s

Flow

–

m³/h

Flow

–

L/min

US data sheets

–

US gpm

vs plain water

–

flow factor

Freeze point

–

°C

Checks

Water pipe sizer

Velocity and friction loss for every size in the range, with the smallest size that meets both limits picked out.

Result

–

Recommended size–

Velocity

–

m/s

Friction

–

Pa/m

Per 10 m of pipe

–

kPa

All sizes

Velocity (bar to max)Within both limits

Checks

Pump head

Add up the index circuit: pipe friction, fittings and component pressure drops. Gives the pump duty point and power.

Result

–

Pump head–

Head

–

With 10% margin

–

kPa

Pipe velocity

–

m/s

Pipe friction

–

Pa/m

Hydraulic power

–

Shaft power

–

Where the head goes

Checks

Expansion vessel

Vessel size, pre-charge and fill pressure for a sealed heating or chilled water system.

Result

–

Vessel size–

Pre-charge

–

kPa (set empty)

Cold fill pressure

–

kPa

Max working

–

kPa

Expansion

–

Expansion

–

% of volume

Acceptance factor

–

usable share

Pressure ladder

Checks

Flow regulating valve

Balance with any manometer. For a balancing valve, measured ΔP gives the flow and the setting for design flow. For a PICV, it sets the dial and checks there's enough ΔP for the valve to control.

Valve type

Valve

Make and model Size Setting (turns)

–

Measurement

Measured ΔP across valve (kPa) Design flow (L/s)

Fluid

FluidFluid temp (°C)

Valve not listed?

Result

–

Measured flow–

50%75%100%125%150%

Checks

Duct sizer

Size a duct by friction rate and velocity limit, the same way you'd use a ductulator. Gives round and rectangular options.

Result

–

Round duct–

Velocity

–

m/s

Friction

–

Pa/m

Velocity pressure

–

Rectangular options

Checks

Unit converter

Type in any box and every other unit updates. Built for reading US data sheets on NZ jobs.

Result

–

Metric–

Handy references

Motor current & imbalance

Full load current from power, and voltage and current imbalance on 3-phase supplies, with motor derating.

Result

–

Full load current–

Checks

Run capacitor check

Work out a run capacitor's actual µF from the current through it and the voltage across it, with the unit running. Uses 50 Hz, as in NZ.

Result

–

Measured capacitance–

−20%−10%rated+10%+20%

Deviation

–

% from rated

Allowed range

–

µF

Formula

–

× A ÷ V

Checks

Cable voltage drop

Voltage drop along a copper cable run, with the smallest cable size that stays inside your limit.

Result

–

Voltage drop–

Drop

–

At the load

–

Smallest that passes

–

mm²

By cable size

Checks

Fresh air

Required outdoor air for the space (NZBC G4 via AS 1668.2), compared with what the system is actually bringing in.

Space Space type

Floor area (m²) People (blank = from density) Density (m² per person) Rate (L/s per person) Area floor (L/s per m²)

Editable defaults. Check the rates against AS 1668.2 Table A1 for the edition named on the building consent or compliance schedule.

Measured outdoor air

OA airflow measured (L/s)

Result

–

Of required outdoor air–

0%50%100%150%200%

Checks

Kitchen exhaust

Commercial hood exhaust rate, overhang, make-up air and discharge duct. A grease duct checklist is in Inspection checklists.

Hood

Hood type Cooking type Hood length (m) Hood depth (m) Cooking surface to hood edge (m)

Cooking line

Appliance line length (m) Appliance depth (m)

Design factors

Capture velocity (m/s) Surface rate (L/s per m²) Min overhang (mm) Make-up air (% of exhaust) Duct velocity (m/s) Measured exhaust (L/s, optional)

Defaults change with cooking type. Check them against AS 1668.2 (kitchen exhaust hoods) and the hood maker's data. An engineered hood may be rated lower.

Result

–

Hood exhaust–

Overhang

Checks

Stair pressurisation

Door opening force from the pressure difference, plus a floor-by-floor test log for SS5 escape route pressurisation.

Criteria (from the design / AS/NZS 1668.1)

Min ΔP, doors shut (Pa) Max ΔP (Pa) Max door force (N) Min open-door velocity (m/s)

Set these from the fire engineer's design or the commissioning baseline. Criteria differ between editions of AS/NZS 1668.1 and between designs.

Door

Door width (m) Door height (m) Handle to door edge (m) Closer force, system off (N)

Test log by level

Enter ΔP with all doors shut. Leave door force blank to calculate it, or enter a measured force from a spring balance. Velocity is the average across the open door with the design number of doors open.

Result

–

Levels passing–

ΔP by level

Checks

Fume cupboard

Face velocity across the sash opening (SS11, AS/NZS 2243.8), with average, spread and exhaust flow.

Result

–

Average face velocity–

Checks

Record on a fume cupboard test sheet

Inspection checklists

Inspection and test checklists for specified systems: pass, fail or N/A on each item, with notes, readings, photos, a defect list and signature. Produces an inspection record PDF for the BWOF file.

Your inspections

Ohm's law (VIR / PVA)

Enter any two values and the app works out the rest. In AC mode it adds power factor and 3-phase, giving kW, kVA and kVAr.

Result

–

Result–

Formulas used

Commissioning sheets

Commissioning records for a high-wall split, a ducted or package unit, or a refrigeration unit. Use them for new installs or for recommissioning after work. They cover client, location, model and serials, charge, pressure test and vacuum, drain test, running readings, photos and signatures, and produce a PDF for your QMS file and the customer.

CoC & ESC

Electrical Certificate of Compliance and Electrical Safety Certificate, laid out like the WorkSafe template. It covers the content required by the Electricity (Safety) Regulations 2010 (regs 66, 67 and 74A), plus a circuit test record. Only a licensed electrical worker can certify prescribed electrical work.

Fume cupboard test sheet

Performance test record for a laboratory fume cupboard (SS11, AS/NZS 2243.8). It pulls face velocity readings from the fume cupboard calculator and covers smoke containment, the airflow alarm, exhaust and stack, and cupboard condition, with photos, signatures and a PDF.

Feedback

Something not working, giving a wrong answer, or could be more useful? Tell us here. It goes straight to the developer.

What's it about Type Which part of the app Which bit of it

How much does it affect you?

Tell us more One-line summary What happened? What did you expect? Steps to make it happen (optional)

Include The values currently entered in that calculator (helps reproduce it; no client or job details) App version, screen size and browser (no personal data) You can contact me about this (uses the email on your email app)

Field calcs for NZ HVAC/R techs

Saved jobs

Forms

Recent

Settings

Data

Feedback

About

Data sources

Room sizer

Cooling load breakdown

Suggested unit type

Code & compliance checks

Duct traverse

Against design

Profile

Air changes per hour

Compared with typical range

Toilet exhaust

Basis & checks

Recovery cylinder safe fill

Checks

Superheat & subcooling

Superheat against target

Subcooling against target

Diagnosis

Coil ΔT capacity check

Against rated capacity

Checks

Nitrogen pressure test

Your tests

Pressure over time

Checks

Assessment

Water flow

Checks

Water pipe sizer

All sizes

Checks

Pump head

Where the head goes

Checks

Expansion vessel

Pressure ladder

Checks

Flow regulating valve

Request a valve

Checks

Duct sizer

Rectangular options

Checks

Unit converter

Handy references

Motor current & imbalance

Imbalance against limits

Checks

Run capacitor check

Checks

Cable voltage drop

By cable size

Checks

Fresh air

Checks

Kitchen exhaust

Overhang

Checks

Stair pressurisation

ΔP by level

Checks

Fume cupboard

Checks

Inspection checklists

Your inspections

Open defects from last visit

Other defects or notes

Sign off

Ohm's law (VIR / PVA)

Formulas used

Commissioning sheets

CoC & ESC