TM59:2026 ,What Has Actually Changed?

In 2014, I worked on the early design of a large modular central cooling plant in the Middle East.More than a decade later, I went back to that Basis of Design with a different question:What can we learn from an old project, and how would we design it better today using the experience, technology and knowledge we have gained since then?In this episode, I revisit the original concept and explore how past project experience can improve the way we approach today's designs - from the very early BOD stage.We look at modular plant design and phasing, TSE and cooling-tower water strategy, sand separation and side-stream filtration, partial-load operation, whole-plant efficiency, thermal storage, controls and future resilience.The technology has evolved, but perhaps the bigger lesson is how our design thinking and decision-making can evolve from one project to the next.That is where experience becomes design leadership.#MEPToday #BOD #DesignLeadership #Redesign #HVAC #DistrictCooling #ModularPlant #MiddleEast #MEP

What happens when water, wind, earth and architecture begin to work as one system?In this episode of MEP Today, I return to Abarkuh in central Iran and follow the story beyond the Nabadan Qanat.Beneath the historic city lies a network of qanat routes, rock-cut chambers, payabs, water storage and underground passages extending across an estimated 60 hectares of the historic fabric.Above ground, windcatchers use natural air movement. Yakhchals produced and stored ice without mechanical refrigeration. Water powered mills, supported gardens and supplied the ancient cypress of Abarkuh.But what interested me most was not any single technology. It was the way these systems worked together .shade, thermal mass, natural ventilation, water, underground space and human behaviour.The lesson is not to copy the past. It is to understand the environment first.They were not fighting the environment. They were dancing with it.MEP Today . People, Places, Better Buildings.

TM59:2026 introduces significant changes to the way overheating risk is assessed in UK homes, including operative temperature, new occupancy profiles and formal recognition of elevated air speed from ceiling fans.In this episode of MEP Today, I look beyond the headline changes and explore some of the practical questions that arise when the methodology is applied to real buildings.How should operative temperature and mean radiant temperature be interpreted within a room? Where should fan air speed be assessed — and at what height? How do occupant position, activity, room geometry and multiple ceiling fans affect the result? And how should these effects be demonstrated consistently in dynamic thermal modelling?I also compare the approach with ASHRAE 55:2023 and ISO 7730:2025, and consider what further guidance may be needed if TM59:2026 is incorporated into future regulatory compliance.A practical discussion about the gap between a compliance methodology and the thermal environment experienced by the occupant.

How can life survive for thousands of years in a cold desert?In Abarkuh, central Iran, a cypress estimated to be around 4,000 years old became the starting point for a much bigger question: how did people, buildings and landscapes survive in such a dry and demanding climate?This episode follows the story of the ancient Nabadan Qanat part of a wider network of qanats across Abarkuh and explores how one flow of water could support gardens and agriculture, drive watermills, contribute to cooling through sardabs, and connect with the tradition of yakhchals, or Persian ice houses. We also look at the wider climate-responsive architecture of Abarkuh: windcatchers, courtyards, pools, shade and thermal mass and how these elements worked together rather than as isolated technologies. A story about water, air, earth and architecture and about learning to work with nature rather than against it.

CIBSE has published TM59:2026, almost nine years after the original overheating methodology was introduced.But what has actually changed for designers and building-performance modellers?In this episode of MEP Today, I compare TM59:2017 with the new 2026 edition and look at the changes that can directly affect an overheating model, including the revised bedroom criterion, window-opening controls, ceiling-fan allowances, mechanically ventilated spaces, communal areas and internal-gain profiles.We also look at the new passive-first, three-stage modelling approach and an important practical question around ceiling fans: when TM59 refers to an air speed of 0.6 m/s, how should that performance be demonstrated in the occupied zone?Not everything has changed and understanding what remains the same is just as important as understanding what is new.

How did people create comfortable spaces in Dezful when summer temperatures could exceed 45°C , without chillers, refrigerants or air-conditioning?In this episode of MEPtoday, I explore the Shavadan, a traditional underground space that uses depth, thermal mass, natural ventilation and human adaptation to create a more stable indoor environment.We look at temperature, humidity, mean radiant temperature, airflow, adaptive comfort, and some unanswered questions such as CO₂ and acoustic performance.The lesson is not to copy the past, but to understand how people worked with their climate.A way of dancing with the microclimate.References:Masoudi Nezhad, Tahbaz & Mofidi Shemirani , thermal behaviour of Shavadan, Souzangar House, Dezful.Babaee & Heidari (2025) , thermal comfort and structural optimisation of Shavadans.Babaee, Heidari & Matzarakis (2026) , thermal comfort in underground and above-ground residential spaces in Dezful.MEPtoday - People, Places, Better Buildings.#MEPtoday #Shavadan #PassiveCooling #SustainableDesign #VernacularArchitecture #ThermalComfort #NaturalVentilation #AdaptiveComfort #BuildingServices #MEPEngineering #ClimateResponsiveDesign #Dezful #IranianArchitecture #Microclimate #LowEnergyDesign

Free Basis of Design pack → meptoday.com/starter-packsTwo engineers. Same qualification, same software — sometimes even the same Excel file. One stays a calculator for their whole career. The other becomes the person who makes the decisions and helps the company grow. The difference has almost nothing to do with the maths.In this first episode, Mohamad Tabatabaee - Chartered MEP Consultant with 25+ years of experience - explains the single shift that separates a design engineer from a design leader: controlling the assumptions behind the calculation. With a real project example (and the 800-drawing "blame game" that follows a late change), plus the one habit you can start on your very next project.In this episode:- Why software and even AI can calculate faster than you — and why that's not the point- How senior engineers know which assumptions are critical- What a Basis of Design (BOD) actually protects you from- The assumption register: what to write down before the brief changesDownload the free Basis of Design starter pack: meptoday.com/coursesNext episode: going deeper into the assumption register and the red-flag checklist.

In this episode of MEP Today, I discuss some of the industry feedback and practical concerns around the TS1 draft version for heat networks.The discussion covers localisation of data, operational behaviour, document hierarchy, thermal storage, manufacturer concerns and how changing occupancy patterns - particularly after COVID and hybrid working — may impact hot water and heating demand assumptions in real projects.The episode also explores the wider question of how standards should balance compliance, operational reality and future flexibility across different building types and energy centre arrangements.Industry feedback on the TS1 draft remains open until 25 May.

Rethinking Heat Network Design with TS1 (intro)

This episode explains how defining the Basis of Design early helps avoid major BCW and DHW sizing issues. Learn about diversity factors, flow rate methods, and the codes that shape reliable hot and cold water system design.