MEP Load Estimation at Concept Stage: Electrical, Cooling and Water From the Equipment List

At concept stage, list every item of equipment with its rated kW, duty and heat to space, apply diversity to get a maximum demand, add a growth allowance of about 15 to 20 percent as NBC 2016 suggests, and convert to kVA at the supply authority's power factor. Cooling and water follow from the same list. The result sizes plant rooms and budgets before drawings exist.

What does the equipment list need to say?

A load estimate is only as good as the list it starts from, and the list is usually the process engineer's, written for another purpose. Ask for these columns for each item: description, location, rated input kW (not only shaft kW), voltage, duty (continuous, intermittent, standby), starting method, heat released into the room, water use, and whether it is existing, planned or future. Mark which items run together in the worst hour of the year.

NBC 2016 Part 8 Section 2 asks that the supply authority be consulted early on feasibility, and says the wattage per square metre and permissible diversity depend on the building type, such as industrial, commercial or hospital, and on city grading so that future loading is accounted for. A factory is not an office; do not borrow office densities.

How do you get from the list to electrical demand?

NBC 2016 sets the sequence: load assessment and application of a suitable diversity factor to estimate the full-load current is the first step, made for every circuit, submain and feeder. Power factor, harmonics and the efficiency of loads are considered, and the diversity factor is based on one's own experience or on its table. The code adds that an allowance of about 15 to 20 percent should be made for extension in the near future.

Here is the arithmetic with invented numbers, to show the steps. They are not benchmarks for any plant.

The result is a number to size the incoming supply and the transformer against, together with the DG set for the loads that must run in an outage. Fire pumps and other standby units are not in the normal maximum demand but belong on the emergency schedule. Transformer selection is a separate step, covered in the HT connection and substation approval guide, and the DISCOM's contract demand rules apply.

Three cautions follow from the code. The diversity table in NBC 2016 covers households, small shops, offices and small hotels, so take utilisation for process loads from the process engineer, not from a table written for small premises. Power factor is not a detail: licensees generally stipulate 0.90 or better, so size correction capacitors, and watch harmonics from drives. And the growth allowance is a minimum for near-term extension; ask whether the client has a phase two.

How do you estimate the cooling load at concept stage?

The code requires a cooling and heating load estimate before HVAC equipment is designed and installed, and lists what it should take in: indoor temperature, humidity, air velocity and activity; outdoor design conditions; building construction and orientation; fenestration and shading; occupancy; ventilation and infiltration; internal loads from equipment, computers and lighting; effective volume; and occupancy, lighting and equipment schedules. It also asks for a suitable diversity factor based on usage, for off-peak loads at night and on weekends, and for anticipated future changes.

At concept stage you will not have all of these. Take the conditioned floor area and the occupancy from the brief, convert installed electrical equipment in conditioned spaces into heat gain (the electrical input of the equipment, less any heat taken away by process cooling or exhaust), add the ventilation load for the fresh air needed, and apply the building envelope allowance for the site. Use the chiller capacity calculator for the plant size and remember that one TR is 3.517 kW. Replace this with a full calculation at design development, and keep the concept figure for plant-room areas and budget only.

Two code observations help the early decisions. For a water-cooled plant the cooling tower footprint is 0.07 to 0.10 square metres per TR for mechanical-draft towers, and the code notes that centralised systems usually prove more cost-effective when the total building load exceeds 100 TR, depending on climate and use. Evaporation from the tower is usually about 1 percent of circulation, which feeds the water estimate.

How do you estimate water demand?

Water has three parts. Domestic and flushing demand comes from headcount and NBC 2016 Part 9 Section 1, Table 1. For factories where bathrooms are provided it gives 30 litres per head per day for domestic use plus 15 for flushing, a total of 45; where bathrooms are not provided, 20 plus 10, a total of 30. For offices including canteen it gives 25 plus 20, a total of 45. Process water comes from the equipment list: boilers, washers, compressors, cooling towers. Fire water is a reserve set by the fire design and the fire authority, and it sits in the tank volume, not in daily demand.

Cooling tower make-up is the part most often missed. At about 1 percent of the circulating flow for evaporation, plus drift and blow-down, a circuit circulating 500 cubic metres an hour needs several cubic metres an hour of make-up. Put it on the schedule with its own tank, which the code asks to be kept separate from the drinking water tank.

Which mistakes undersize the plant rooms?

• Nameplate as demand. Adding every rated kW without diversity oversizes the incoming supply; ignoring starting currents and standby duties undersizes the DG. Do both calculations on purpose.
• Standby counted as running. A duty/standby pair is one load, not two, but the room must hold both machines.
• No growth room. The code's 15 to 20 percent is for load. Space for the next transformer, chiller or pump is a layout decision made now.
• Cooling counted twice. Chiller power belongs in the electrical schedule once, and its heat rejection belongs in the tower sizing.
• Ignoring the supply authority. Contract demand, power factor and HT or LT thresholds can change the layout of the electrical room.
• Heat from the equipment room itself. Panels, transformers and drives release heat into their own rooms that needs ventilation or cooling.
• Water treated as an afterthought. Tower make-up, process water and the fire reserve can double the tank volume that a headcount alone suggests.

The MEPF cost calculator turns a first set of loads into a budget range, and our guide to the MEP design brief lists the information to collect. Later stages are in MEP design deliverables by stage.

How Secured Engineers helps

Secured Engineers' MEP design consultancy prepares load schedules, plant room layouts and the drawing sets that the Fire NOC, CEIG and DISCOM applications need, all in-house, and the same team can build the works as a single MEPF contract with solar. Fire NOC, CEIG and DISCOM net-metering filings are prepared in-house. We work from offices in Noida (Delhi NCR) and Ludhiana, across 535+ projects in 18+ states, with 89.77% repeat clients.

If you have an equipment list and a concept layout, send them and we will review the load assumptions, the growth margin and the plant room areas, and tell you what we would change. The service is described on design and approvals. Message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.