Wet Bulb temperature; and why it’s the most important thing you’ll learn about today.
If you are a scientist, engineer or air-conditioning sales person, then you’ll know about wet bulb temperature.
If however, you don’t fall into any of these categories then (A) thank you for clicking on this article and (B) you’ll likely not have come across wet bulb temperatures since some very easy-to-forget GCSE science classes.
Lets start at the beginning
Nearly 8 years ago I was sat in the Bristol offices of Daikin UK receiving training from two industry legends; Kevin Gregory and Mark Hutton.
What these two don’t know about air-conditioning isn’t worth knowing, their knowledge is second only to the patience they showed me.
To say I was wet behind the ears (pun intended) was an understatement, fortunately, Kevin & Mark were able to utilise some pretty handy tools that Daikin has for this sort of thing.
Below is a very useful (and not at all intimidating) psychrometric chart, something that our staff and customers will know and love. Or at least know.
When working for a Heating, Ventilation, and Air-Conditioning (HVAC) company, one of the most important things you have to understand is temperature.
The temperature that we see on weather reports, and that we all use, is called the ‘dry bulb temperature’.
This means it doesn’t account for humidity.
Once the dry-bulb temperature gets above ~35degC, we start sweating to cool down. Stinky armpits and stained white shirts yes, but we know what we’re dealing with, and humans can physically cope.
The wet bulb temperature includes humidity, and so is a lot higher in real terms. Basically, it covers the important detail that sweating won’t cool us if there’s too much moisture in the air.
To measure it, you cover a thermometer in a damp cloth and swing it around. Seriously.
Essentially, the higher the humidity, the closer the wet-bulb temperature is to the dry-bulb temperature.
Once the wet-bulb temperature goes above 35degC it becomes so hot that sweating no longer works, and the body can no longer cool itself.
So when working with building service engineers, understanding the building design conditions is fundamental for us to correctly design and size HVAC systems.
This is all very interesting, but has Ryan used another click — bait title to draw me in or am I actually going to learn something important today?
India
In March, April and May of last year (2022), India and its neighbours endured repeated heatwaves that exposed more than a billion people to dangerously hot conditions.
India broke several temperature records. The warmest March in more than a century was recorded across the country and a new high of more than 49C was hit in Delhi in May.
India is moving towards fatal climatic conditions.
This year (2023) saw the country’s hottest February in 122 years, and it is only likely to get worse.
Summer temperatures in northern India regularly soar beyond 40°C in May and June, the hottest months of the year. Topping 50°C is unusual, but that is happening, too.
Climate scientists are now worried about an increased possibility of deaths if human body temperatures exceed the “wet bulb” threshold of 35°C.
A Lancet study found a 55% spike in fatalities in India between 2000–2004 and 2017–2021 due to extreme heat.
This is besides the loss of labour hours and the resultant loss of income.
This is happening all around the world, right now. Many people, societies and countries are going to struggle massively with the rising temperatures and humidity levels brought on by the climate crisis.
See this article by Anthony Signorelli about the vulnerability of the people of Costa Rica.
Back home
People and governments all around the world will be looking into different forms of climate mitigation and building climate resilience.
And it’s not just India or other countries that might feel far away, here in the UK we’ve experienced the hottest days ever recorded — over 40degC in July 2022 — with the hottest winter temperatures too/ the warmest February on record.
Is it time that we started preparing for the future?
In the UK and across Europe we are going through a monumental shift as we look towards the electrification and decarbonisation of heat.
The UK is responsible for over 505 million tonnes of Carbon Dioxide equivalent.
Space heating alone accounts for 17% of this, 13–14% of which can be attributed to domestic homes.
As we ditch gas and move towards electrification, is it time we started thinking about the future?
Out with the old… in with the new?
Boilers were great, people loved boilers, they were cheap and easy.
But they are dirty; bad with carbon and air quality.
And a little bit limited.
They heat water. That’s about it.
Is COOLING the future of HEAT?
A recent Government report with AECOM, Delta-EE and the University of Exeter reviewed the future cooling demand across the UK;
Although the current demand for cooling is dominated by non-domestic buildings, by the end of the century, it is estimated that the domestic stock will require 75% to 85% of the cooling energy consumption.
Potential synergies have been identified between the increase in cooling demand and heat decarbonisation.
Heat pumps provide low carbon heat and can provide cooling when operating in reverse.
5th generation heat networks allow users to both import and export heat into the network.
An increase in cooling demand may strengthen the business case for 5th generation networks as customers are able to export waste heat from cooling systems into the network and other users can then import this heat.
Hot Mess
As global temperatures continue to rise due to climate change, wet-bulb temperatures are also going to increase, leading to an increased risk of heat-related illnesses and fatalities, especially in regions that already suffer with high humidity.
Over the past few summers, people have been investing in portable air-conditioners and fans to cool themselves down as the heat has become too much in the UK.
Many employees with WFH contracts are choosing to head into their companies offices, not for the pizza days and new standing desks but to benefit from the air-conditioning.
Our buildings are designed so that we can control the indoor climate.
We are the lucky ones.
Things will undoubtedly get hotter. What the future looks like obviously depends on what we do, how much we do and how quickly we do it.
Air conditioning companies and building service engineers alike, we should all be as acutely aware of- and care about- the ambient conditions as much as we do the internal design conditions.
