Over the past two years, I’ve had several opportunities to deliver information on modern hydronics to some less “traditional” audiences. Specifically, those who attended conferences on building weatherization, state-of-the-art air sealing and insulation methods, indoor air quality, and the design of ultra-low-energy-use buildings.
I was asked to speak at these conferences on topics such as “reliable” hydronic systems, how hydronic heating can interface with renewable energy sources, and ways that hydronics technology can be tailored to low-energy-use homes.
Initially, I was a bit apprehensive about how well these topics would be received by those who attend such gatherings. However, I soon discovered new audiences that craved information on how modern hydronics could be customized for their specific needs. The exit surveys indicated these topics were among the best received of all those presented, and that attendees were eager for follow-up information.
Fresh FacesThe people who attend these conferences represent a demographic quite different from the heating contractors who usually attend seminars on hydronic heating. Most of them have not worked with hydronics over the last couple of decades. Most are not familiar with concepts such as outdoor reset control, hydraulic separation, radiant walls and ceilings, or other design approaches that many hydronic pros now consider common practice.
From what I saw, these conferences attract a high percentage of younger people who are passionate about dealing with energy waste in the building industry. They want to deliver buildings, both new and remodeled, that are comfortable, energy-efficient, sustainable and, when justified, make reasonable use of renewable energy. They want what properly applied modern hydronics technology can deliver - they just don’t know what’s possible or available.
Specialists who design ultra-low-energy-use buildings, and those who design and install typical home heating systems, could be likened to ships passing in the night.
The building specialists are highly focused on the building’s thermal envelope, but still in need of a “solution” that provides reliable comfort at very low rates of heat transfer. They don’t necessarily keep up with what the hydronics industry has to offer. Some also have had less-than-satisfying experiences with those in the heating trade who simply want to “shoehorn” in the standard systems they use in other houses, regardless of their applicability to ultra-low-energy-use homes. This inevitably creates the impression that the “mainstream” heating industry doesn’t understand or care about what low-energy-use building specialists are trying to accomplish.
Approaching the situation from the other direction, many in the mainstream heating trade are not familiar with evolving building concepts such as “net-zero” homes, heat recovery ventilation, superinsulation or passive solar design. They view such concepts as experimental or even fanatic, ignoring the fact that fuel prices and other market forces will inevitably lead us to lower-energy-use buildings.
As an example, the 2012 edition of the International Code Council’s energy code is targeting a 30 percent drop in building energy use, relative to what was required in 2009. Whether we get there by market forces or through code mandate, there is no question in my mind that we are headed for significant reductions in building energy use in the years ahead.
Lost OpportunitiesAlthough the North American hydronics industry has a lot of hardware that when properly combined could yield systems that are ideal for such buildings, few of those in the industry are currently reaching out as “solution providers” to those building ultra-low-energy-use houses.
As proof, I’ve not seen a single company that offers hydronic heating solutions exhibiting at these conferences, where upwards of 800 attendees make the time to attend and pay top dollar to be there.
Maybe it’s time our industry extend its presence beyond the traditional plumbing and heating contractors who flock to more traditional HVAC gatherings such as the AHR show. Why not be one of the first to build brand recognition among the ultra-low-energy building designers?
What kind of mechanical system fits the needs of these builders? Here’s a listing of the qualities I feel should be part of the solution.
1. A highly efficient, modestly sized, modulation/condensing, sealed combustion heat source. It could be a “box” that goes on the wall, or an assembly that fits onto or into a storage vessel. For reasons that will become apparent as you read on, a burner turndown ratio of 3:1 is very sufficient. There is no need to complicate the solution with the controls and sensors necessary to achieve high turndown ratios such as 10:1. This is true even though the system will use room-by-room zoning.
2. A very well-insulated storage vessel. Think of it as an oversized Thermos bottle designed for a high degree of vertical temperature stratification (hot at the top, significantly cooler at the bottom). Heat from the heat source is parked within the thermal mass of this storage vessel until needed by the room-by-room zoned distribution system. This vessel provides the buffering mass that prevents what has become the Achilles heel of many mod/con boilers - short cycling under low loads.
This thermal mass also provides a way to deliver “bursts” of domestic hot water at rates that may be significantly greater than what the heat source could supply on a steady basis. If upsized, this vessel could also serve as the storage tank for a modest array of solar thermal collectors.
3. The solution would include a homerun distribution system, based from a single valveless manifold. Half-inch PEX or PEX-AL-PEX tubing would run from this manifold to a properly sized panel radiator in each room. Each panel radiator would be equipped with a nonelectric thermostatic radiator valve. This would allow each panel to continually adjust its heat output to match changing solar or other internal heat gains.
Such gains can have a much more pronounced effect on comfort in super-insulated houses. A low-mass panel radiator with a thermostatic valve has the necessary response characteristics to deal with this.
4. All flow through the distribution system would be handled by a single small ECM-powered, pressure-regulated circulator with a peak electrical input demand of 40 watts or less.
5. Domestic water heating would be provided instantaneously through a small, stainless-steel, brazed-plate heat exchanger mounted outside, yet close to the storage vessel. A flow switch similar to those used in other “tankless” water heaters would engage a “microcirculator” that would immediately move hot water from the storage vessel through the primary side of the heat exchanger.
The low mass and high internal surface area of this heat exchanger would have hot domestic water flowing out the other side within one or two seconds. If this heat exchanger ever fouls or fails, it could be easily replaced without disturbing the storage vessel or other parts of the system.
6. If solar collectors will be included with the solution, or added in the future, they will be configured, along with the storage vessel, for drainback freeze protection. There is no need for antifreeze, heat dumps or diverting valves. A single, variable-speed collector circulator would operate at full speed to “prime the siphon” of the collector loop, and then drop back to a reduced speed based on the temperature rise across the collector.
7. Under most conditions, water temperature within the storage vessel would be controlled based on simple outdoor reset. If the solar option was included in the solution, a mixing valve would be used to protect the distribution system from what might be very hot water in the storage vessel at the end of a sunny day.
All these features need to come together in a way that makes the product into an “appliance” rather than a collection of several hundred individual components that are assembled on site. The latter approach, while dominant over the last three decades of hydronic heating, is simply too complicated and time consuming to be seen as a packaged “solution” by those designing low-energy-use houses. It’s simply a nonstarter with this crowd, and for good reason.
A schematic showing one way that most of the above requirement could come together is shown in Figure 1.
This schematic is not the final way these hardware concepts will go to market. Most of the individual components shown will need to be preassembled into a compact, fully serviceable appliance.