I am what could be described as a thermostat nerd. I enjoy walking into mechanical rooms where boilers are modulating along with some sort of smart control driving the ship. Unfortunately, I generally see boilers short cycling like crazy while supplying 180°F water all year round. While modern boilers are great, we have millions of homes currently operating without ideal controls.
There are a couple system-related conversations I have over and over. A statement I still hear from contractors is, “You can’t do an outdoor reset curve with baseboard heat. You need to use a setpoint 180°F supply for it to work.”
You absolutely can put a reset curve on baseboard. For many years, baseboard output charts may not have even shown ratings below 160°F supply temperature. That wasn’t because baseboard won’t work at lower tem- peratures; it was because if it got any cooler the boilers would risk condensing. At the time, that would have been bad for non-condensing boilers. Modulating/condensing boilers are at their best with the lower return tempera- tures and at their worst at setpoint 180°F.
I will concede that buildings with undersized base- board runs may not heat with 100°F water on a design day. However, the other 360-non-degree days of the year you can heat buildings with cooler temperatures. The baseboard output only needs to meet the heat loss of the building, which will be a fraction of the BTUs you would need on a design day the vast majority of the year. For example, you may be able to keep a room warm on a 50°F outdoor temperature day with either a steady stream of 110°F supply water or short cycles of 180°F water. The first option will help your condensing boiler con- dense and it will be less wear and tear on its components.
If you don’t believe me, check out a report published by Dr. Thomas A. Butcher. In 2004, he published a paper titled, “Hydronic Baseboard Thermal Distribution System with Outdoor Reset Control to Enable the Use of a Condensing Boiler.” As my coworker Greg Gibbs asks, “Do you know who paid for this study?”
You did. The study was prepared for the U.S. Department of Energy with your tax money.
You can have the best of both worlds. Baseboard sys- tems can run with lower temperatures and you can avoid callbacks from cold customers, if you control the system properly.
Another argument I hear a lot is that boiler controls are so sophisticated that you don’t need additional smart controls in the house. This can be true in some cases. A well-placed supply sensor can help limit boiler cycles and target the best temperature. Buffer tanks are another great tool to alleviate short cycling. Yet, there is no replacement for a network of sensors and thermostats communicating to a central brain that drives the boiler. Imagine driving a car without being able to see more than ten feet in front of you. Would that be an easy way to avoid obstacles? The further ahead you can see, the bet- ter decisions you can make. The same is true for boilers with sensors in multiple places in the building.
Control upgrades can be money well spent for home- owners, too. For example, if a homeowner was told that they could spend $15,000 to install a new boiler that could decrease their gas bills 10 to15 percent they may be interested. Sometimes, those same houses have boilers with some life left in them that don’t need to be replaced. The homeowner could spend $2,000 on bet- ter thermostats and controls to save that same 10 to 15 percent. Sophisticated control systems may be closer to 30 percent, depending on what they were using before.
On a long enough time frame, a boiler will need to be replaced. Contractors aren’t robbing themselves of a bigger sale by selling controls. They are helping to use the homeowner’s money wisely, and also making them more comfortable if the boiler was short cycling, under heating, or over heating zones.
Great controls increase the likelihood you will get to the AFUE efficiency rating on the side of your boiler. Does AHRI test boilers in houses? No, they test them in labs. They test with a short vent, at low altitude, good gas quality, and sub 100°F return temps. That is how a boiler can achieve greater than 95 percent AFUE. If you take that same model boiler and put it in a house with undersized baseboard and run it at 180°F all year, you’ll struggle to get above 87 percent thermal efficiency.
The types of control systems I’m referring to are beyond a basic programmable thermostat. Being able to schedule a thermostat is helpful, but to see significant gains, you have to have some sort of modulation control over the boiler. ENERGY STAR found that out the hard way.
Directly from ENERGY STAR’s website, “The ENERGY STAR specification for programmable ther- mostats was suspended on December 31, 2009 and the ENERGY STAR label is no longer available for this category. Manufacturers were required to cease using the ENERGY STAR name and mark in association with all products manufactured on or after December 31, 2009. While EPA recognizes the potential for programmable thermostats to save significant amounts of energy, there continue to be questions concerning the net energy savings and environ- mental benefits achieved under the previous ENERGY STAR program- mable thermostat specification.”
ENERGY STAR found, “Many households (perhaps 30 percent or higher) with programmable thermostats may be unable, unwilling, afraid, uninterested, or otherwise reluctant to deploy default programs or to create or deploy custom pro- grams.”
Another study from the Energy Center of Wisconsin found no dif- ference in energy intensity between houses with or without program- mable thermostats. Admittedly, pro- grammable thermostats are much easier to program now than they were even five years ago. Still, a setback schedule isn’t the only piece of the puzzle.
The major trend I see in commer- cial applications is a shift towards BACnet or other automation pro- gramming languages. The nice part of these systems is that contrac- tors can configure exactly how they want the system to act with different brands and types of products. They can send and receive signals from equipment, pumps, and valves as they choose. The disadvantage of these systems is control contractors sometimes use all of this capacity just to build a big, expensive pro- grammable thermostat.
Controls are the most often over- looked part of the energy equa- tion. Boilers and major components are generally where we start when we look to upgrade a building, but they won’t hit their peak efficien- cies if controlled poorly. I would even argue that broken equipment is related to poor control as much as any other factor.
Do the people at Nest and your local BACnet controls contractor know everything about complex hydronics? You do. The control busi- ness is a huge part of our efficiency equation, but it is slipping out of our fingers to less knowledgeable par- ties. If you don’t have a cool hydron- ics control system that you know and love, find one. There is too much business and too much importance in thermostat systems to give to other sectors. n
2.www.ener gystar.go v/index. cfm?c=archives.thermostats_spec
3. .www.energystar.gov/ia/partners/prod_development/revisions/down- loads/thermostats/Summary.pdf
4. https://law.resource.org/pub/us/ cfr/ibr/004/hi.BTS-2000.2007.pdf
Max Rohr has worked in the hydronics and solar industry for 10 years in the installation, sales and marketing sectors. Rohr is a LEED Green Associate and is RPA’s Education Committee Chairman. He can be reached at email@example.com and @maxjrohr.com.