Ten Trends In North American Hydronics
John Siegenthaler, PE
If you’ve followed the Hydronics Workshop column over the years, you’ve seen my periodic prognostications on future trends in North American hydronics. Although our industry has certainly progressed over the last 25 years, there are several areas where we lag behind other parts of the world. There are also instances where state-of-the-art technology from other industries has not been fully implemented into the day-to-day practices of our industry.
Increasing energy prices will eventually drive our market in directions similar to other parts of the world - most notably Europe. It’s just a matter of time until the “pain factor” inflicted on American consumers is sufficient to bring about substantial and lasting changes in a culture so accustomed to cheap energy.
Some future market directions also will be driven by unique North American “wants” rather than needs. A good example is abundant quantities of domestic hot water. Although one might look at such a want as wasteful in comparison to other cultures, there is no denying that a market exists and will be supplied until such time that these “wants” become illegal or are no longer desired by our culture.
Here is my list of things to watch for in the next few years:
1. Residential chilled water cooling. One of the “hottest” emerging topics in hydronics technology is chilled water cooling for residential structures. The same physical properties that make water the ideal material for transporting heat to a load also make it ideal for moving heat away from a load. The size of the piping required to distribute chilled water to a cooling load is much smaller than the ducting required to distribute cooled air to the same load. This allows for less-invasive installations. The zoning of a hydronic cooling system is also much easier and less expensive than equivalent zoning using forced air.
Chilled water in the range of 40-50 degrees F is ideal for cooling. When circulated through the proper equipment, it’s capable of providing sensible cooling (air temperature drop) as well as latent cooling (moisture removal). Water in this temperature range can be produced using water-to-water geothermal heat pumps, or from air-cooled condenser units located outside the building.
The latter units can use refrigerant line sets between an outdoor condenser and interior refrigerant-to-water heat exchanger. This eliminates water in the outdoor unit and, thus, eliminates the need for winter drainage or other means of freeze prevention. A schematic for this type of chilled water combined with zoned air handlers is shown in Figure 1.
The ultimate cooling distribution system in terms of distribution efficiency is something called a “chilled beam.” The idea is to circulate chilled water through a finned-tube heat exchanger suspended above a decorative valence near the ceiling. This valence also collects condensate and may even serve as a housing for lighting and small ventilation ducting. Most chilled-beam systems operate with passive air distribution (e.g., no fans or blowers). The greater density of the cooled air allows it to fall into the room as warmer air rises to replace it. This lowers the operating wattage of the distribution system to that of the chilled water circulators.
Chilled-beam cooling is gaining traction in commercial cooling applications within North America. Given its significantly better distribution efficiency, I think this technology will soon migrate into residential applications.
2. Btu metering. I’m absolutely convinced that centralized heat production in combination with heat metering will grow in North America as energy prices increase and the free market searches for ways to conserve without sacrificing thermal comfort. It’s a great solution for condo, apartments, strip malls and leased office spaces. It’s also a great way to leverage hydronics into a project. We’ll be discussing it in detail in next month’s column.
3. ECM-based smart circulators. In my opinion, the transition to ECM-based circulators will be one of the largest paradigm shifts in North American hydronics in decades. It’s already under way and will soon pick up momentum - think months rather than years.
Imagine circulators that match the peak performance of our present-generation hardware while operating on half the input wattage. Compound those savings with the ability to instantly adapt to the moment-by-moment flow requirements of a system. Here’s the concept: As soon as a zone valve closes, the smart circulator detects the “attempted” change in differential pressure and reduces speed to counter this tendency. Every time speed goes down, so does electrical power demand.
Estimated electrical savings relative to current-generation circulators is 60-80 percent. That’s pretty hard to ignore, and much greater than incremental savings achievable from any other potential hydronic system refinements that I’m aware of.
Just as outdoor reset provides “cruise control” for the thermal energy flow within a hydronic system, ECM-based smart pumps provide cruise for the hydraulics. My advice is to read up on ECM-based circulator technology. Here’s an excellent Web site that will give you a glimpse of what’s now happening with this technology in Europe (www.energypluspumps.eu/en/cesky/Aboutproject/what_is.html).
After that, keep your eyes open for opportunities to replace older circulators in systems using zone valves or thermostatic radiator valves with ECM-based smart pumps. It’s probably one of the “greenest” things you can be doing as a hydronic-heating professional.
4. Zoning with valves rather than circulators. Here’s a topic that has elicited strong opinions as long as I’ve been in this industry. Although both forms of zoning work, there’s little doubt that a properly designed system using zone valves in combination with the new ECM-based circulators will use significantly less pumping energy than an equivalent system having fixed-speed zone circulators. I believe this combination will become the dominant method of zone control in future systems.
2,500-square-foot house in a cold climate, with full room-by-room zoning, operating
on 40 watts of pumping power on a design day. The February 2007 Hydronics
Workshop column showed you how to do this, and it’s very different than the
“wall-full-of-pumps” approach that seems in vogue with the North American
hydronics industry these days. It’s time for us to move on to methods that are
appropriate for the decades ahead. (Visit the PM archives at www.PMmag.com; free registration is
Although P/S systems have served our industry well and will continue to hold a market share in the future, the benefits they offer (e.g., hydraulic separation of individually pumped circuits) are achievable without need of a primary circulator. One less circulator lowers installation cost. More importantly, it lowers life-cycle operating cost, in many instances by well over $1,000!
The use of multifunction hydraulic separators (those that also perform air and dirt separation) will increase in North America. These devices will increasingly serve as the “interface” between new mod/con boilers and existing distribution systems as shown in Figure 2. They also will be used in new installations in lieu of traditional P/S piping. These devices are already available from several sources in North America. Eventually the term “hydraulic separator” will be as common as “closely spaced tees” in the vocabulary of North American hydronic pros.
6. Lower temperature systems. This trend started years ago with the infusion of modern radiant panel heating methods from Europe. It has continued to gain acceptance as mod/con boilers have gained market share. Its future is assured by ever-increasing energy prices.
For years I’ve suggested limiting the upper water temperature in any hydronic heating system to 200 degrees F. In most cases, this water temperature is only necessary when a heat exchanger for domestic water heating or snowmelting is in use and high rates of heat transfer are needed. Its higher than necessary for new baseboard or panel radiator installations, and I really cringe when someone tells me they’re operating a radiant floor system at a 200-degree F water temperature.
So why do water temperatures need to come down in the future? It’s the same old argument reinforced by increasing energy prices. Lower temperature systems improve heat source efficiency, reduce distribution losses, increase the ratio of radiant to convective heat output from panel radiators, and certainly improve safety.
Eventually it will probably be illegal to design American hydronic heating systems for 200-degree F water temperatures. Some areas in Europe have already drawn the legal limit at 75 degrees C (167 degrees F), and it’s inevitable our codes will take us in that direction in response to energy prices and the “greening” of America. We should embrace this concept now rather than wait for codes to force it on us. The greater upfront cost of larger heat emitters required at lower water temperatures will be returned in fuel savings over the life of the system.
7. Web-accessible/networked components. Almost everyone who works in a field requiring frequently updated information relies on the Internet as the conduit for that information. Digital downloads, such as operating system updates for computers, make the concept of waiting for a service tech to come to the site to make adjustments seem antiquated.
Why shouldn’t hydronic systems benefit to the fullest extent possible from the information superhighway? Imagine boilers, circulators and system controls that use the Web to automatically update their operating characteristics for improved performance. Picture systems that could intelligently take advantage of real-time energy pricing. Even better, think about querying the devices in a hydronic system located far from you using the computer in your office or home, and then making adjustments without ever visiting the site. It’s all possible and it’s all starting to happen in North America.
I’m aware of at least three North American control manufacturers now offering Web-accessible control products suitable for residential and light commercial hydronic systems. More will be implementing this capability in the very near future. It’s important for hydronic professionals to understand how these systems work and what their capabilities are. They will soon be as ubiquitous as the Honeywell T87 was in its day.
8. Wireless sensors and thermostats. Think about how much time you would save by not having to run cable to every thermostat and temperature sensor in a modern hydronic system. Imagine the ability to easily move a thermostat or sensor within the building as the use of the space changes over time.
Wireless devices are all around us in the form of phones, Internet routers, automobile keys, security systems and home entertainment hardware. Most of these devices handle much more information in a given time than is required to maintain a room at a set temperature.
Wireless room temperature controls do exist if you know where to look. Several were on display at the ISH Frankfurt show in March. We need a serious and sustained offering of such devices in North America.
9. Increased use of homerun distribution systems. I serious doubt I will ever design another series loop baseboard system, or for that matter another system based on diverter tees. Not because these systems don’t work, but because another approach offers better performance at lowered cost. That approach is called a homerun distribution system. One example of such as system was shown in Figure 1, another is shown in Figure 3.
Homerun systems use individual circuits of small-diameter PEX or PEX-AL-PEX tubing to carry flow between a central manifold station and each heat emitter. That emitter can be a fin-tube baseboard, panel radiator or fan-coil unit, or a combination of these.
Homerun systems are ideal for retrofit jobs because they’re minimally invasive to the structure. They’re also a great way to make use of the “remnant” pieces of tubing left over from radiant panel installations. The parallel configuration of a homerun system reduces circulator power requirements relative to series or diverter tee layouts. It also delivers the same water temperature to each emitter, allows for room-by-room zone control, and permits room-by-room balancing when necessary. Series piping systems offer none of these benefits.
If you install fin-tube baseboard using the classic soldered-copper-tubing approach, you owe it to yourself to try a homerun system on your next installation. Once you do, I can virtually guarantee you’ll never go back to series circuits of soldered copper tubing. Homerun systems should soon become the standard for room-by-room hydronic distribution systems in North America.
One of the most profound differences I noticed was the insulation used on storage tanks for European systems. It was common to see at least 3 inches of polyurethane insulation on such tanks - top, bottom and sides. In North America, we might currently accept a sales line such as “This tank only loses 1/2 degree F per hour” as adequate. That’s not the case over there. They expect tanks to retain heat like a high-quality Thermos® bottle.
I recently spoke with a German heating engineer who was “on tour” to learn more about North American hydronics. He was dumb-founded by the lack of insulation on our systems. He was used to designing systems that put a precise amount of heat exactly where it belongs. Isn’t that our goal as well?
If you buy the argument that insulation isn’t needed as long as the piping and components are contained within the thermal envelope of the building, consider this: When was the last time you stood in a mechanical room, on a design day, with properly functioning equipment, and the air temperature was about 70 degrees F? Chances are that mechanical room had an air temperature in the 80s or even 90s, given all the heat coming off the boiler jacket, uninsulated piping and other components.
A mechanical room at 90 degrees F loses heat to 0-degree F outdoor air 38 percent faster than a mechanical room at 65 degrees F. There’s simply no reason to maintain a mechanical room at normal human occupancy temperature. Kind of makes you wonder why some engineers still specify unit heaters in mechanical rooms. I guess it’s just in case there isn’t enough heat leaking away from all the other hardware in the room.
Having It Both Ways
I’m sure you’ve spotted a common theme during the discussion of these trends. They are all driven to some degree by the need to conserve energy.
During the energy crisis of the 1970s, it was not uncommon for Americans to compromise their comfort to reduce energy use. Anyone who’s ever lived in a passive solar house with a wall full of south-facing glass can attest to this. I believe the lack of commensurate comfort was the main reason Americans abandoned many energy-conservation strategies as heating fuel prices declined and stabilized during the ’80s and ’90s. Given the present opulence enjoyed by most Americans, it’s unlikely the “sacrifice comfort to conserve energy” scenario will ever repeat itself.
Today we have hydronics technology within our grasp that allows significantly reduced energy consumption relative to common practice, and does so without sacrificing comfort. As hydronic professionals, we must continue emphasizing this unique and unrivaled combination to consumers who seek both. This duality is the trump card we hold relative to other heating and cooling options. It’s also the basis for a strategy that won’t be quickly abandoned in the unlikely event that energy prices take a sudden drop.
Turn the page on old practices, and look back only when it’s time to measure how far forward the industry has moved.