Blizzard Testing Your HVAC System
Can you tell it’s winter yet? Is it safe to come out yet? Here in the North East, Mother Nature has just finished her first major storm of the season. We can confirm that no one at Procure is interested in living in the far, Arctic North after experiencing days-straight of subzero temperatures. We were within spitting distance of water being able to freeze before it hits the ground. Along the way, we also got to push our heating systems to their edges and see where we really should’ve built things differently.
Edge Case Testing
During normal operation, it’s doubtful you’ll ever see something out of place in a well designed heating system. If you engineered a system for an average winter, then chances are you can turn your home or office any temperature you like during average weather. It can be ten degrees outside, but a sweltering 92 inside. When nature throws you a curve ball you get to see where the weaknesses are in your heating system. More extreme weather, is more stress on the system. More stress is going to show you what parts can’t keep up.
This breaks down to a problem of numbers. The sum-total of heat you can put in the air is XX. Your building loses heat to the air at a rate of YY. Severe winds increase this rate by ZZ. In order to stay warm XX needs to be greater than YY + ZZ. It needs to be possible to get ahead of the energy losses to the environment.
As the environment grows more extreme, it becomes not just a problem of X, Y, and Z. You start to see what component isn’t performing. Perhaps the furnace is cycling normally, yet the building is freezing. Perhaps the furnace is behaving erratically with overheating and shutting down. Maybe the furnace barely runs, yet it’s unbearable?
Extremes will amplify any flaws in a design. A misplaced thermostat will allow cold pockets to form more readily in the building. Poor insulation will help form cold pockets in the outer edges of the building. Improperly sized heating components will create all manner of strange behavior. We get to look at the individual components and see the consequences of a bad decision more readily than just waiting for the weaker part to fail.
The Fault in My System
The heating system for my home had an interesting fault all its own. I have hot water heat, which his circulated through baseboard radiators in every room. Every room has its own radiator along the wall. During the big blizzard, the heater cycled normally. It ran anywhere between one and three times an hour to keep up with the demand for hot water. The circulator pump ran frequently. We never hit our target temperature of 70 degrees. It was a struggle to hit 64.
At first glance, this could be an issue with the thermostat. It could be that the heater simply couldn’t keep up with the demand for energy. It could have been some sort of limit or safety or timeout being tripped that forced the system to take a break.
It was undersized radiators. During the blizzard, there was a little plumbing spill that left a nice, big puddle of boiling water in the kitchen (my life is not boring). It warmed the room up towards the 80s without causing the rest of the house to get any colder. We added energy to the air, without subtracting any from our output.
Let’s look at that equation
Heat capacity – (Environmental Heat Loss + Accelerated Wind Losses) = Temperature Change
Heat Capacity is not equal to furnace output. It’s equal to the radiator output, so long as the furnace can sufficiently saturate the radiators. The furnace could saturate the entire building in hot water, but the radiators could not transmit that heat into the open air fast enough to overcome our losses to the environment.
In my situation, we could power additional radiators, used fans to assist the energy transfer from the radiators, or install larger radiator assemblies to counteract the extreme cold. Not every component in the system is sized to match. The furnace does need to produce more heat than is necessary for the baseboards, in order to provide hot water for the sinks, showers, and washers. In this case however, we have a huge gulf between what we can produce and what we actually use.
This Isn’t a Problem
This was an edge-case experience, which is an important thing to keep in mind when we look at our heating and cooling systems. If a week or two out of winter is a bit chillier inside, we can offset that with clothes and electric heaters. Don’t panic if a huge storm barrels through and your furnace works harder for those days. It’s something to be expected and learned from. In my case, I now know that about 20 below is where this heating installation starts to really have trouble. Winters here don’t go below ten degrees most of the time. That’s not something to redesign and ruin a system over.
On the flipside of the coin, if your furnace is struggling all winter long, it’s time to consider some upgrades. If you know where the weak parts are, you can consult with your HVAC Contractor to upgrade and replace those components or if necessary design an entirely new system or work out ways to supplement the heating with improved insulation, insulated pipes, or whatever it takes to reduce your heat losses.