Expert instructor Dave Yates answers student questions with customer anecdotes on the Fundamentals of Radiant Heating discussion board
Student 1: I’ve seen two references in the course to “high temperature” ceiling panels needing to be at least 8 feet above the floor. Is this to prevent children from touching them, or is it to limit the heat in the upper part of the room? Or is it something else?
Dave Yates: Proximity to the human head! Remember the balance for thermal comfort and how the body loses its heat. We want to avoid the floor being too warm (why we limit FST to the body’s average skin surface temperature) as we’re in more-or-less direct contact (conduction) with it. We don’t walk on the ceiling, so those surface temperatures can be hotter, but we do need to be mindful of proximity to the head as that’s a heat/cold sensitive part of our anatomy.
I once got a call from a couple who couldn’t locate the heating source in their recently purchased home. I met with them, and told them to turn down the thermostat for a day before my scheduled visit, and turned up the T87 stat. Within minutes, I knew where their heat was and that it was radiant. Specifically, it was ceiling embedded radiant installed in the 1940’s. Just like the radiant heat felt from a campfire on a cool evening- I could easily sense the radiant was above my head. I asked them if they had noticed any wall access panels in closets. They had, and that’s exactly where we found the individual black iron 3/8″ circuits with balancing valves as well as the 1/8″ copper tubes with bleeder valves that run up to connect with each loop at the high spot. While there, I sold them a new boiler with primary/secondary piping for the three zones and outdoor reset (before modcons were available in the USA).
Today, I would have taken along my Flir infrared camera and we would have been able to “see” the circuits as if we had X-ray vision.
Student 2: In addition to the injection pump controller is it also necessary to have an additional outdoor air reset controller on the boiler? Or would that boiler controller be part of the manufacturer supplied trim package?
Dave Yates: Great question! In order for injection piping to work (and justify its use/expense), the source temperature must be hotter than the required injection delivery points of use. If your designs call for water delivery temperatures below 120°F on a design day, you could certainly utilize an outdoor reset control on a standard it’s ON/OFF non-condensing boiler and carve out a bit more ECV for your customer.
If outdoor reset is a built-in feature on the ON/OFF boiler and you are utilizing low-temperature zones, injection piping is one of your options. You can also utilize thermostatic mixing valves.
In one historic farm house (7th generation homeowners), we retrofit three radiant zones to mix with two standing cast iron radiator zones while installing a new oil-fired direct-vent boiler. The radiant zones were the laundry room, bathroom, and kitchen. The radiant water delivery temperatures required varied for each room and when I crunched the numbers, I discovered the return water from the hottest room’s water delivery temperature was the delivery temperature required for the second hottest and that its return water met the delivery temperature for the third room! That allowed me to use just one thermostatic mix vlv and eliminate the additional manifolds and circs or zone valves if I had maintained separation between the three rooms. I was able to treat it as one zone while piping it as a cascade. The radiator zones were served water from the oil boiler, which had outdoor reset. The advantage of outdoor reset and the radiant mixing valve is that as the boiler resets, so does the TMV ratio. The end result is a better ECV (Essential Climate Variables), return on investment, and comfort for the customers.
Enroll in Fundamentals of Radiant Design, taught by RPA legend Dave Yates. This is a foundational course for anyone doing hands-on work in the radiant or hydronics industry. It provides the foundation for a long and productive career., Dave Yates will teach you state-of-the-art information about radiant heating technologies, giving you the leg up on competition and providing you with unlimited opportunities in radiant heating design and installation.
Check out Dave’s FREE Mastering the Outdoor Reset Curve course:
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