Turn a tested plant room sketch into a scaled, dimensioned layout. Tab 1 lists what has to fit, sized from current manufacturers’ data and shown as ranges across them. Tab 2 lays it out to scale with the service and airflow clearances drawn, checks it against the five plant room questions, and prints at 1:100. Tab 3 sizes the risers. It opens on a worked example: press Clear on tab 1 and enter your own Assignment 2 plant. Every size here is a concept-stage allowance; a real product selection governs.
The rest of the session uses no tab: Step 1 (Plant room visit), which comes first on purpose, so test your hand sketch in the real room before you open this; Step 2 (How HVAC concepts are planned in practice); the air path and water path items on the Step 3 checklist; Step 4 (Defending your concept) and Step 5 (IOA rehearsal in pairs).
Chillers, boilers and air-handling units have got smaller and lighter, but the space manufacturers ask for around them has not: room to pull the tubes out of a chiller, to slide a coil out of an air-handling unit, for air to reach the coils of a heat pump. The box is not the space requirement. So each item below is shown with its clearances as well as its box, and as a range across current manufacturers’ data rather than one product.
Enter your Assignment 2 plant: design capacities, how many machines, the plant types and a riser group for each part of the building with its own zone system. The tool also adds the items that are easy to forget: pumps, buffer tanks and hot water storage. Air-handling and outdoor-air units are sized from your own loads, not a fixed rate per square metre.
Machines. Each cooling or heating machine takes the design capacity divided by the number on duty. A standby (N+1) is one more machine of the same size: it adds space and weight but no capacity. Cooling towers follow the chillers one for one, each rated for the chiller it serves.
The range. For each machine the tool takes the units in the manufacturers’ data whose capacity is within 70–140% of the size you need (or the three nearest if fewer than two are that close) and reports the spread of their length, width, height and operating weight. The box drawn on tab 2 is the largest length, width and height among those units, so a real selection of that size should fit inside it. A size outside the data is flagged: split the plant into more machines, or check a manufacturer’s range directly.
Clearances. Each item carries one allowance (the figures on its card), chosen from the manufacturers’ stated service and airflow clearances, with their spread shown underneath. A water-cooled chiller’s tube-pull zone is drawn as a separate hatched zone the length of the unit at one end. It may run out through a door or louvre, which is how real plant rooms avoid giving it floor space.
Large water-cooled chillers. Above about 2,400 kWr per machine the data has only conventional centrifugal chillers, which are two to three times heavier per kW than screw and oil-free chillers of the same capacity.
Where things go. Water-cooled chillers, boilers, pumps, tanks and storage default to the plant room; cooling towers, air-cooled chillers, heat pumps and VRF outdoor units to the roof or a plant deck. Air-handling and outdoor-air units default to the roof (a weatherproof unit or a roof plant room); move them into the plant room on tab 2 if that is your scheme.
All-air VAV. Supply airflow per m² = sensible load (W/m²) ÷ (1.2 × supply temperature difference). At 60 W/m² and 10 K that is 5.0 L/s per m². Multiplied by the group’s floor area it gives the air-handling unit airflow, split into units of no more than 17 m³/s (the largest size in the data).
Air-handling unit size (fitted to one manufacturer’s 11 sizes and checked against a second): width ≈ 0.95 √Q m (0.78–1.11), height ≈ 0.66 √Q m (0.57–0.79), length 3.97 + 0.11 Q m (compact: mixing box, bag filter, coils, plenum fan) to 6.05 + 0.11 Q m (generous), dry weight 500 + 160 Q to 720 + 180 Q kg, with Q in m³/s. Length depends on the number of sections, not airflow, which is why even a small unit is about 4 m long. The tool draws the compact length and the middle width and height, and uses the generous weight for floor loading.
An assumption that carries weight: the access allowance. Manufacturers ask for the unit width plus 0.3 m on the access side to withdraw a coil (1.5–5.0 m by size), 1.2 m for filters and 1.2–2.0 m for a fan. The tool offers two allowances on tab 2: tight, a 1.0 m aisle on the access side, 0.6 m behind and 0.5 m at each end, i.e. (W + 1.6) × (L + 1.0), which assumes the coil comes out through a door or a shared aisle; and full, a coil-withdrawal aisle of W + 0.3 m (at least 1.0 m) and 0.6 m at each end. Neither is a manufacturer’s figure: they are concept allowances built from the figures above.
DOAS (dedicated outdoor air). Outdoor airflow per m² = outdoor air per person ÷ floor area per person + the extra make-up air. At 10 L/s per person, 10 m² per person and 0.3 L/s per m² that is 1.3 L/s per m². The unit is a stacked heat-recovery wheel unit, selected at 70% of its largest airflow (a quieter, more typical selection, about one size up): length 1.7 + 0.17 Q m plus 0.9 m for the chilled and heating water coils in the duct, width 0.95 + 0.23 Q m, height 1.14 + 0.22 Q m, weight 50 + 370 Q kg. The two airstreams are stacked, so check the room height first. Clearance: 1.2 m on the inspection side (0.8–1.1 m stated, 1.1–1.5 m to withdraw a wheel cassette) and 0.8 m at each end for duct connections. Active chilled beams sometimes need more primary air than the ventilation minimum; the tool does not add it.
VRF (comparison only). Outdoor units in systems of up to about 90 kW, two or three modules side by side in one row, with 1.0 m in front, 0.5 m behind and 0.5 m at the ends of the row. Weight is the manufacturers’ net weight, 4.5–6.7 kg per kW, plus 10% for field refrigerant (an assumption: no manufacturer consulted gives an operating weight).
Water flows. Flow (L/s) = kW ÷ (4.19 × temperature difference). The tool assumes 6 K for chilled water, 10 K for heating water and 3 K for chilled-beam water (beams run on 14–17 °C water, so the difference is small). Condenser water follows the cooling tower rating: 0.681 m³/h per nominal tower ton, about 0.054 L/s per kWr of chiller.
Pumps. One duty and one standby pump per circuit, each carrying the full design flow: practice, supported by pump makers’ duty and standby controls rather than by a design guide. Above 120 L/s the tool uses two or more duty pumps and one standby. Each is a vertical in-line pump selected from one maker’s 4-pole curves (an indicative selection, not a supplier’s), on a concrete inertia base 100 mm larger all round and weighing 1.5 times the pump. An assumption that carries weight: the access aisle of 915 mm all round each pump comes from a Canadian university’s plant room standard; no Australian figure was found. Aisles can be shared between pumps in a row. Motors from 5.5 kW need 1 m clear above for lifting the motor off.
Buffer tanks. Chillers need a minimum system water volume of about 3–6 L per kW, and air-source heat pumps in heating 8–13 L per kW. The pipework counts towards it, so a tank only makes up the shortfall. The tool assumes the pipework holds half of the lower figure and draws enough 1,425 L vessels (1.0 m across, 2.27 m tall, room at least 150 mm taller) for the other half. Gas boilers are given none.
Hot water storage. Hotel: 45 L per guest at 65 °C for two guests a room, plus 30% for stratification, about 117 L a room. Apartments: 1.5 times a two-bedroom apartment’s peak-hour figure of 75 L, about 112 L each. At least two vessels. The heat pumps recover the stored water from 10 to 65 °C in two hours, in units of 40 kW (a carbon dioxide heat pump water heater of the kind designed for this duty).
Heat pump capacities in the data are rated at 7 °C outdoors and 45 °C leaving water (one series at 50 °C). None of the manufacturers’ documents used here gives a capacity at 55–65 °C water, so the loss you enter is indicative: a common rule is 20–40% less at 60–70 °C, which is an estimate, not a published figure. The tool sizes each heat pump for its share of the load divided by (1 − the loss).
What the documents do say is where the standard machines stop. The reversible units in the data list a maximum leaving water temperature of 55 °C (two series) or 60 °C (the four-pipe units). Above that you need a high-temperature heat pump on a natural refrigerant (propane or carbon dioxide), which the data shows reaching 70–90 °C. The cheaper answer is usually to design the heating water at 45–50 °C, which fan-coil units and air-handler coils are selected for.
Two further derates are left out: cold-morning defrost in heating, and air-cooled machines on a roof above 35 °C in cooling (western Sydney peaks exceed 40 °C).
The plant space tables long used in design teaching (Parlour, early 2000s) give an area and weight per plant item. Set against current manufacturers’ data with full service clearances, the boxes have shrunk much more than the rooms:
| Item | 2000s table | Box now | With clearances now | What changed |
|---|---|---|---|---|
| Water-cooled chillers, 100–250 kWr | 30 m², 2.0 t | 2.4–2.6 m² | 28–33 m² (pair); 22–24 with tube pull through a door | No real shrinkage: small chillers sit on a minimum frame |
| Water-cooled chillers, 1,000–1,250 kWr | 49 m², 8.0 t | 4.6–7.1 m² | 47–65 m² (pair); 32–42 via a door | 9–46% lighter; room about the same unless tubes pull through a door |
| Water-cooled chillers, 2,000–3,000 kWr | 60 m², 19 t | 7.3–14.6 m² | 66–100 m² (pair); 42–63 via a door | 40–64% lighter (screw and oil-free); room the same or larger |
| Cooling towers, 1,600–1,800 kWr | 68 m², 8.0 t | 18.3–18.4 m² | about 47 m² | 30% less area; operating weight similar |
| Cooling towers, 2,800–3,000 kWr | 99 m², 13.2 t | 23.7–28.9 m² | 62–70 m² | 30–37% less area; operating weight similar |
| Gas boilers, 200–300 kW | 28 m², 5.6 t | 0.95 m² each | about 7 m² (pair) | 75% less area, 86% lighter: the biggest change |
| Gas boilers, 2,000–3,000 kW | 71 m², 28.5 t | 6.6–10.8 m² (pair) | 15–30 m² (pair) | 58–79% less area, 72–75% lighter |
| Air-handling plant, about 1 / 5.7 / 14 m³/s | 9 / 28 / 38 m² | n/a | 14 / 21–24 / 30 m² tight; 17–24 / 30–42 / 46–60 full | Small units now larger (bag filters, plenum fans: about 4 m long minimum); large ones smaller unless a full coil-withdrawal aisle is kept |
| Duct shafts, all-air, 2,000 / 6,000 / 10,000 m² served | 4.9 / 12.1 / 19.6 m² | n/a | 5.0 / 15 / 25 m² (tab 3 method) | The same at 2,000 m²; the older figures fall with size, the method does not |
| Heat pumps, DOAS units, chilled beams | none | see tab 1 | see tab 1 | Not in the older tables at all |
The water-cooled rows assume two chillers side by side with 1.0 m outer aisles, a 1.2 m centre aisle and 1.0 m at the non-pull end, as the 2000s figures are recorded on a two-machine basis. Air-cooled chillers are left out: the basis of the older air-cooled figures (one machine or two) is not confirmed, and the comparison turns on it. The older tables are a summary for comparison only; no size in this tool is taken from them.
The same contrast for heating: at about 600–650 kW an air-to-water heat pump needs about 54 m² of roof with its airflow clearances and weighs 4.3 t, against about 5 m² of plant room and 1.6 t for a gas condensing boiler of the same output. About ten times the area and 2.6 times the weight, and it moves from the plant room to the roof.
The units used for your current selection, with the source of each (numbered as in the list at the foot of the page). Capacities are at each source’s rating condition; weights are operating weights unless marked.
Each item is drawn as its box (solid) and its clearance zone (dashed). Clearance zones may overlap each other, because a real plant room shares access aisles, but not another item or a wall. A chiller’s tube-pull zone (hatched) may run out through the door. The checks say what is wrong and why, and the five plant room questions are answered from your layout at the foot of the tab.
Drag items from the tray onto the plan, or select one and then select a spot. Drag to move; select an item and use the arrow keys (Shift for 0.5 m), R to rotate and Delete to return it to the tray. Drag the empty floor to pan.
A rough first pass packs every item for this area in rows, without sharing aisles. Rearrange from there.
Print at 100% (“Actual size”), not “Fit to page”. Each sheet carries a scale bar: 5 m on it measures 50 mm when the print is true to scale.
Air carries heat poorly: a cubic metre of water holds about 3,500 times as much heat per degree as a cubic metre of air. So a system that moves the sensible cooling to water (DOAS with fan-coil units or chilled beams) needs much smaller duct shafts than an all-air VAV system, and somewhat larger pipe risers. Every square metre of shaft is lost on every floor it passes through.
Each group below is shown four ways, with your choice highlighted. The pipe riser leaving the plant room is on tab 2 as an item to place.
7 m/s default; 5–10.
6 m/s default; 4–8.
Air shaft, for each duct in the riser: area = airflow (m³/s) ÷ velocity × k × 1.2. The 1.2 is 20% spare, as two Australian university design standards require for main riser ducts. Supply and outdoor air run at 7 m/s by default (the maximum one standard sets for riser ducts in offices); return and exhaust at 6 m/s.
Assumptions that carry weight. k grosses the duct up to the shaft it needs: insulation, flanges and a 100 mm working gap. It is 1.5 for an insulated supply duct and 1.35 for an uninsulated return, rising to 2.0 for any duct smaller than 1 m² where the gap is a larger share. These come from geometry, not from a published rule: none was found. Return air is taken as 90% of supply in VAV, and exhaust or relief as 80% of the outdoor air in DOAS (toilet and kitchen exhaust leave through their own risers).
Pipe riser. Chilled water at 6 K, heating water at 10 K and chilled-beam water at 3 K, each with a flow and a return pipe. Each pipe is the smallest steel size whose velocity stays within 2.4 m/s and within one university standard’s limit for that size (1.5 m/s up to DN100, 1.8 m/s at DN150–200). Its footprint is a square of the outside diameter plus insulation on both sides (50 mm chilled, 40 mm heating) plus a 100 mm gap, then 20% spare. With chilled beams the primary chilled water carries the latent and outdoor-air load (the group’s cooling less its sensible load) and the beam water the sensible load. Each group’s cooling and heating are its share of your design capacities by floor area.
VRF (comparison only). Refrigerant pipes are small, so the riser is set by the number of systems: about 0.04 m² for each system of about 90 kW (a worked estimate, not a manufacturer’s rule). VRF still needs a DOAS duct riser for the outdoor air.
Not included: electrical and communications risers (no recognised source for their area was found), hydraulics, fire services, fire dampers (in Australian practice usually at each floor branch, outside the shaft) and a standing zone in walk-in risers.