20 Jul

Picture of the month: HVAC in hot weather

So summer is icumen in here in Cambridge. Here it is certainly following the traditional pattern of an English summer: three days of heatwave followed by a thunderstorm.

All of which has produced some hard times for the cooling systems in the facilities we are monitoring. Take this:

July 1st was the hottest day of the year so far, with temperatures over 32° following on from a couple of days with both warm weather and many hours of sunshine. So not surprising that at 12.15 the HVAC in this office gave up under the strain and couldn’t be bought back online until 15.30.

Picking this apart raises some fun details and questions. It’s worth comparing that week to the week before. Here are the plots for the Monday, Tuesday and Wednesday with the temperature and sunshine plots for those days along side:

And here are the plots for the same days (monday, tuesday, wednesday) on the preceding week.

In this case temperatures overnight in the preceding week were much cooler – you can see the cooling system is working for much less time in the morning to remove the heat. There’s no characteristic sharp drop in temp at 5.30 am.

By the time we get to the week of the 1st July though, external overnight temperatures have risen and the office is holding a lot of heat overnight. In the morning removing that heat is taking more and more time. Furthermore, evening sunshine on both the two preceding days has warmed a portion of the office (on the right hand side of plan) that has always had difficulty in removing heat, so the system was under an immense amount of strain.

Under the circumstances if the system was going to suffer a failure, this is the situation which is likely to trigger it.

After the temperature topped out at 28.2, the cooling was eventually bought back on line, but the damage was done: there was far too much heat in the building to be removed by the HVAC before it was turned off at 7.30 and another warm night overnight meant the repaired system had to work for a much longer period in the morning to remove it, churning away for twice as long as usual.

Lessons learned? If you have HVAC systems that are older and have already identified some hot spots, be ready to take drastic action if you have a period of warm nights and solar gain. You might be operating closer to the edge than you might think.

If you have similar troublespots in your facility and you’d like a better picture of how the summer is affecting them, contact us for a quote on a pilot deployment.