US inpatient hospitals consumed 193.3 thousand Btu of major fuels per square foot in 2018, against 70.4 for the commercial building stock as a whole. The figures come from the US Energy Information Administration's 2018 Commercial Buildings Energy Consumption Survey, released on 21 December 2022. No equivalent public benchmark exists for Mexican hospitals, so treat the ratio as an order of magnitude rather than a local number.

What is local is the invoice. A Mexican hospital sits on a CFE medium voltage tariff. Under the methodology CRE set in Acuerdo A/058/2017, dated 23 November 2017, that invoice divides into charges billed on kilowatt hours, charges billed on kilowatts of measured demand, and an adjustment for power factor applied to the whole amount.

That division decides which efficiency measure is worth money. Ventilation control, automation and rooftop solar all cut kilowatt hours. Only some reach the demand charge. None of them corrects power factor, which is the cheapest item on the list to fix and the one most hospital energy programs never open. A rooftop array can move the measured factor the wrong way, because it cuts the real power drawn from the network while the reactive demand of the plant room stays where it was.

What a Mexican hospital's CFE invoice is made of

Start with the charge the finance office can verify this week without commissioning anything. Under the disposiciones complementarias published in the DOF on 31 October 2000, the supplier applies a surcharge to the invoiced amount when the billing period average power factor falls below 90% lagging. The surcharge is 3/5 x ((90 / FP) - 1) x 100, capped at 120%. At or above 90% the supplier owes a credit of 1/4 x (1 - (90 / FP)) x 100, capped at 2.5%.

Run it. At 0.85 power factor the surcharge is 3.5% of the whole invoice, which is 35,000 pesos for every million pesos billed that month. At 0.80 it is 7.5%. Correct the same site to 0.95 and the charge becomes a credit of 1.3%. A hospital is a motor heavy building. Chillers, air handling fans, pumps, lifts and imaging equipment all draw reactive power, and a plant room whose capacitors were never resized against the present load is the normal case.

A fixed date is attached to this. CRE reissued the Código de Red as RES/550/2021, published in the DOF on 31 December 2021 and in force from 1 January 2022. It requires load centers to hold power factor between 0.95 lagging and 1.0, measured in five minute intervals rather than averaged over the month. That requirement is not enforceable until 8 April 2026. A hospital passing the CFE monthly test at 0.91 can still sit outside the band for hours at a time, and it has a known deadline by which to close the gap.

The rest of the invoice is energy and demand. Energy charges move with kilowatt hours in base, intermedia and punta hours. Demand charges move with measured kilowatts. An efficiency measure that lowers consumption at three in the morning does nothing to the second group.

Ventilation is the largest controllable load and the most constrained

Outside air has to be cooled, dehumidified and often reheated before it reaches a room, every hour the building is open, which in a hospital is every hour. In Monterrey, Mexicali or Mérida that conditioning load runs for most of the year. It is the largest block of energy a facilities manager can influence, and the one with a floor underneath it.

The floors are set by room class. In the US design guidance reprinted by the CDC in its 2003 environmental infection control guidelines, an operating room carries 3 outdoor and 15 total air changes an hour and is held positive to adjacent spaces. An airborne infection isolation room carries 2 outdoor and 12 total air changes an hour and is held negative. Whatever standard your own project was certified against, the structure is the same. Airflow in those rooms is a minimum, not a variable, and no control strategy may cut below it.

So the saving sits in the rooms where the standard permits modulation. Legacy variable air volume boxes do modulate, contrary to how they are often described, but they hold a fixed minimum airflow regardless of what the room is doing. Adaptive control resets that minimum against measured conditions. Demand controlled ventilation goes further and modulates outdoor air against occupancy, using presence detection or carbon dioxide measurement. It works in consultation rooms, waiting areas, offices, teaching space and catering. It does not apply in the rooms above.

This is worth engineering rather than estimating because of the fan law. Fan power varies with the cube of airflow, so cutting airflow by 20% in a zone where the standard allows it takes fan power down by roughly half. Before pricing anything, get the conditioned floor area split by room class from the facilities drawings. That split, not a percentage, is the size of the prize. The same arithmetic drives the HVAC economics in Mexican hotels, where the conditioned load is similar and the room class constraint is absent.

What building automation moves and what it does not

A building automation system schedules and resets setpoints across lighting, air handling and chiller plant. Where a zone is reliably unoccupied at known times, that cuts kilowatt hours. A hospital's clinical core is never one of those zones. The addressable area is administration, outpatient clinics, teaching space, catering and plant rooms, and the business case has to be built on that area rather than on the whole building.

On the demand charge the answer is narrower. Scheduling alone does not lower the measured peak. Only a control strategy configured to limit or shed load against live demand measurement does that, and it has to be commissioned with the clinical engineering team so no medical load is ever inside the shed list. Mexico Energy Partners has not published a measured before and after for a Mexican hospital automation project, so no percentage is offered here. What can be established on your own site is the profile, and that starts with a detailed energy audit and twelve months of interval data.

What onsite solar can reach in a building that never closes

Two statements about rooftop solar circulate in Mexico and both are wrong as usually written. The first is that no permits are required below 500 kWp. Article 17 of the Ley de la Industria Eléctrica, published in the DOF on 11 August 2014, exempts generation below 0.5 MW from holding a CRE generation permit and exempts nothing else. The project still needs an interconnection contract with CFE Distribución and a bidirectional meter under the Manual de Interconexión de Centrales de Generación con Capacidad menor a 0.5 MW, published in the DOF on 15 December 2016. It also needs an electrical installation certified against NOM-001-SEDE-2012 and municipal construction and land use approval. In a hospital, add the internal clinical and infection control review of any work on an occupied roof.

The second is that there are no installation costs. That describes a lease or an onsite power purchase agreement, where a third party owns the system and bills per kilowatt hour delivered. Buy the array outright and it is capex. The structure is a commercial choice, not a property of the technology, and the article that sets out what a rooftop solar project in Mexico actually requires goes through both.

Then there is the shape of the load. A hospital draws power through the night and an array does not generate then. Under CRE's distributed generation rules, issued as RES/142/2017 and published in the DOF on 7 March 2017, surplus daytime output under medición neta is credited against later consumption rather than paid in cash. Credit unused after twelve months is liquidated at the local marginal price of the node. The demand charges stay on the invoice either way. A hospital drawing several megawatts also cannot serve much of that load inside the distributed generation regime, because 0.5 MW is the ceiling above which a generation permit and a different contractual structure apply.

Where to start

Take the invoice before the equipment. Pull twelve months of CFE bills and the interval data behind them, and read the power factor line first. It is already measured, it costs nothing to check, and it applies to the whole invoice rather than to one line of it. If the site is below 90%, size reactive compensation now and set the work against the 8 April 2026 Código de Red date.

Then list conditioned floor area by room class and mark the zones where the ventilation standard permits modulation. That list bounds both the ventilation project and the automation scope, and it is the single document that stops a hospital buying controls for rooms that are not allowed to use them. Price generation last. An array quoted against a bill you have already cut is a smaller and better decision than one quoted against today's.

Sources

• US Energy Information Administration, 2018 Commercial Buildings Energy Consumption Survey, Table C12, released 21 December 2022. Major fuels energy intensity of 193.3 thousand Btu per square foot for inpatient health care and 70.4 for all buildings.
• Comisión Reguladora de Energía, Acuerdo A/058/2017 of 23 November 2017. Methodology for the final basic supply tariffs, and the split into energy and demand charges.
• Disposiciones complementarias a las tarifas para suministro y venta de energía eléctrica, DOF, 31 October 2000. Power factor surcharge and bonus formulas and their caps.
• Comisión Reguladora de Energía, RES/550/2021, Código de Red, DOF, 31 December 2021, in force 1 January 2022. Power factor band of 0.95 lagging to 1.0 in five minute intervals, enforceable from 8 April 2026.
• Centers for Disease Control and Prevention, Guidelines for Environmental Infection Control in Health-Care Facilities, 2003, reprinting the AIA Guidelines for Design and Construction of Hospitals and Health-Care Facilities, 2001. Air change rates and pressure relationships by room class.
• Ley de la Industria Eléctrica, DOF, 11 August 2014. Article 17, generation permit exemption below 0.5 MW.
• Secretaría de Energía, Manual de Interconexión de Centrales de Generación con Capacidad menor a 0.5 MW, DOF, 15 December 2016. Interconnection contract and bidirectional meter.
• Comisión Reguladora de Energía, RES/142/2017 on generación distribuida, DOF, 7 March 2017. Medición neta credits and the twelve month liquidation at the local marginal price.
• NOM-001-SEDE-2012, Instalaciones eléctricas, DOF, 29 November 2012.