Worked cases · Tokyo

One machine, four rooms, and the hour it can only do one thing

A 20 HP outdoor unit and four 14 kW indoor units on one pair of refrigerant lines: 23 kWh/m² a year for cooling and heating both, and a two-pipe limitation the model refuses to hide.

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Meguro is one 600 m² office floor — four perimeter rooms of 150 m² — served by a variable-refrigerant-flow system: four 14 kW indoor units on one 56 kW (20 HP) outdoor unit, sharing a single suction line and a single liquid line. Four times fourteen on fifty-six is a connection ratio of 100 %, which is where ISO 15042 and AHRI 1230 rate a multi-split and where this outdoor unit is validated against a maker's own published capacity grid. Each indoor unit serves its own room and modulates to it; the outdoor unit is asked for the sum of what they take, at the coldest evaporating temperature any of them settled at, and its capacity is shared out by what each room is asking for that hour.

On Tokyo's year the four coils do 52.5 MWh of cooling and 17.7 MWh of heating for 9.5 MWh at the outdoor unit plus 4.2 MWh of indoor fans — about 23 kWh/m² a year for both jobs, which is what a VRF is bought for. Heating is the same machine run backwards: the indoor coils condense into their rooms while the outdoor coil takes the heat out of the weather and pays the defrost penalty for it.

The interesting hour is the one where the rooms disagree. A January afternoon with the offices full and the sun on the south side genuinely wants cooling in one room while another still wants heat — and a two-pipe machine cannot do both at once. The model picks the direction the whole manifold's demand asks for and the disagreeing room waits: 25 unmet heating hours in the north over the year, 29 unmet cooling hours in the south. Those hours are not a modelling failure to be smoothed away. They are the reason three-pipe heat-recovery VRF exists, and this model does not yet have it — so the page says so.

What it reads on Tokyo

Coil duty	52.5 MWh cooling / 17.7 MWh heating
Electricity	9.5 MWh at the outdoor unit + 4.2 MWh of indoor fans — 23 kWh/m² a year
Rooms	19.2–25.0 °C; unmet 0–29 cooling hours, 0–25 heating hours
Humidity	2 900–3 100 hours a year above 0.012 kg/kg — a VRF without a dedicated outside-air unit does not control it
Connection ratio	100 % (4 × 14 kW on 56 kW), the ratio the standards rate at

What it taught

A manifold has one direction an hour. Letting each indoor unit choose fed a cooling coil a heating capacity at the other end's condensing temperature — not a state, and the first winter morning found it as a non-finite solve.
An indoor unit cannot be offered more than it is rated for: alone on a machine four times its size, a 14 kW unit was offered all 85 kW of it, and a duty a coil cannot pass runs its condensing temperature off the chart.
A VRF indoor unit has no reheat, so declaring a room humidity ceiling only makes it over-cool: the same building with the ceiling did 90.8 MWh of coil duty on 14.6 MWh of electricity against 52.5 and 9.5 without, and bought about 7 % of its humid hours for it.

The machines

Sources

ISO 15042:2011 §6.1.1.2 and ANSI/CAN/AHRI 1230 §6.2.2.1.2 (multi-split rating at unity connection)
DOE Commercial Prototype Building Models, Medium Office (occupancy, setback, gain densities)
PVGIS TMY, Tokyo

Readings of the shipped model on the building's own PVGIS typical meteorological year; engineering estimates from catalog data and published correlations. The building runs on every plan, including Free, a few times a day.