TM59:2026 . Operative Temperature, MRT and the Ceiling Fan Challenge
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.
30 Sept 2026
Nabadan Qanat - From Qanat to Cypress
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.
25 Sept 2026
TM59:2026 ,What Has Actually Changed?
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.
21 Sept 2026
Shavadan: Dancing with the Microclimate , Passive Cooling Before Air Conditioning Part 1
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
1 Jul 2026
EP1 - From Calculation to Leadership: the shift that changes your career
Free Basis of Design pack → meptoday.com/starter-packs
Two 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 changes
Download the free Basis of Design starter pack:
meptoday.com/courses
Next episode: going deeper into the assumption register and the red-flag checklist.
17 May 2026
TS1, Operational Reality and the Challenge of Local Behaviour
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.
29 Apr 2026
Are We Designing for Reality… or Assumptions?
Rethinking Heat Network Design with TS1
(intro)
13 Nov 2025
Getting the BOD Right: Early Agreement for BCW & DHW Design
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.
3 Nov 2025
BOD - DW 172
In this MEP Today episode, we break down DW 172: Commercial Kitchen Ventilation — the key standard for designing safe and efficient systems. Learn about airflow, hood design, filtration, and compliance tips for high-performance
21 Oct 2025
BOD Ventilation – Designing Air from the Start
Early clarity on BOD Ventilation sets the foundation for every successful project.
In this episode, we discuss how updated BCO 2023 and CIBSE Guide A guidance is reshaping design practice — from realistic occupancy assumptions to measurable IAQ targets.
Better decisions at the concept stage mean fewer changes, healthier spaces, and verified performance.
29 Nov 2022
Introduction of series 2
Series two focus is about the exchange information platform.
8 Mar 2021
CDP part 1 BMS
Review the specilaist feedback about the design stage
1 Dec 2020
Career Anchors part 5
Career anchor and impact of the first job on the professional career journey
19 Oct 2020
career Anchors part 4
Career anchor and impact of the first job on the professional career journey
15 Sept 2020
career Anchors part 3
Career anchor and impact of the first job on the professional career journey
25 Aug 2020
Career anchor part 2
Career anchor and impact of the first job on the professional career journey
19 Jul 2020
Career Anchor
Career anchor and impact of the first job on the professional career journey
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