Thermal comfort, elegance & efficiency
for commercial buildings
By Peter Biondo
Green design and energy efficiency are becoming paramount to architects and engineers designing space heating systems for commercial buildings. One type of heating system gaining the attention of designers is hot water baseboard radiation influenced by the use of attractive flattened or tubular steel-rolled panel-style radiators. Beyond their basic function as heat emitters, modern panel radiators can be particularly elegant and may be creatively integrated into the architectural element. They are manufactured in a wide variety of shapes, sizes, and colors that allows for installation in just about any condition. Controlled by thermostatic radiator valves for independent zone control and to modulate warmth, 24V thermostats and wiring are not required. Installed with energy-saving features, such as the use of variable speed circulators and temperature setback, these fuel-efficient systems meet the high standards for energy efficiency. Plus, there is more to being green than just energy savings — even in the current economic climate, sales of these systems for commercial buildings are on the rise. There are opportunities at hand for savvy rep firms and suppliers who can package, support, and sell these products.
Avant-garde design
It’s no accident that style and energy savings are driving the use of these European-influenced panel radiators. These panel-style heat emitters are stylish and in vogue with architects and interior designers, and the hydronic heating savings features are desirable for engineers—especially those who want to be perceived as “green” avant-garde companies. The radiators themselves are versatile and impressive. Panel radiators may be specified as baseboards or as wall or vertical panels; they can be modular, or installed as linear beams mounted on a ceiling or wall. Radiant panels can be used in hospitals, nursing homes, day care centers, commercial office buildings, schools, museums, security facilities, airports, churches, banks, laboratories, swimming pools, factories, and workshops. They are commonly built into high-rise condos, commercial offices and remodeled commercial buildings.
The steel-rolled panels are durable, easy to maintain, and relatively light. Unlike their heavy cast iron ancestors, panel radiators can be wall mounted. They feature silent heat delivery and have a fast thermal response time. They are suitable heat emitters to install in either new construction or retrofit. Overall, these stylish emitters with thermostatic radiator valves offer a sound solution for providing a desirable blanket of comfort at any outside temperature with optimal fuel efficiency. Therefore, it is no surprise how energy conservation, appeal and comfort are powerful market forces for hot water heating, or why a designer may not go directly to forced air for heating.
Non-electric proportional actuation
A control feature that makes panel radiator systems of such great utility is the use of thermostatic radiator valves and thermostatic operators for controlling the warmth of the emitter and the room temperature. The radiator valves themselves are proportional flow devices for the panel radiators. A thermostatic operator, attached to the radiator valve, contains a small metal liquid-filled sensing bulb that contracts and expands in response to the ambient temperature. This sensor drives a piston in the thermostatic operator, which opens and closes the radiator valve stem within the valve body. The quick-acting liquid-filled sensors in the thermostatic operator modulate the flow for the heating requirements of the room. Many features are common to thermostatic radiator valve operators. Thermostatic operators have a wide temperature control range of 40–85°F and have temperature limiting and locking capabilities. Many have automatic freeze and shut-off protection. Designed with an open air head and a long isolation stem, a well-engineered thermostatic operator prevents the interference of temperature from the valve body. There are lock-shield rings or protection caps to help prevent theft of, or damage to, the thermostatic head. There are special operators designed for high traffic and dorm activity. For example, there is a thermostatic operator, commonly known as the university model or landlord model, which is difficult to vandalize or break and has a sheer lateral strength of 230 lbs. Typically, a smashed or damaged thermostatic operator will give full flow through the thermostatic radiator valve and into the panel radiator. If the head is broken off of the university model, the radiator valve will restrict flow to 5%, eliminating full flow through the emitter. Also, for temperature limiting or setting, the university model requires a special tool.
Radiator valves are also unique in that they have valve inserts available, which are designed for special applications or to correct problems. Valve inserts may be installed into the thermostatic radiator valve for pressure differentials of up to 40 psi for commercial baseboard to self regulate balance. There is a valve insert to correct the problem of a reverse supply/return hook-up. There is another valve insert that balances flow through the radiator valve. A huge benefit to using thermostatic radiator valves is ease of service. The valve insert may be removed for service, or be replaced under working conditions, by use of a special tool.
The thermostatic radiator valve and the thermostatic operator are installed on the supply side of the panel radiator. A return-side radiator valve may be included for balancing the flow rate when the thermostatic radiator valve is fully open, thereby setting the temperature drop across the panel radiator. The return valve comes with features such as positive shut-off, drain capabilities, and a memory stop. Thermostatic radiator valves and return-side radiator valves are selected and paired together for towel bar warmers or exclusive radiators. They are also manufactured in different angle patterns for the piping connections and for the location of the thermostatic operating head in relation to the radiator.
There are a variety of thermostatic operators for modulating flow through a thermostatic radiator valve. Familiar models are installed on the radiator valve at the emitter. For better control of room temperature, there are thermostatic operators with remote sensors. These are especially useful with radiators that are installed within an enclosure. But for many applications, the popular operator is the remote thermostat. Wall mounted, the thermostat is convenient to adjust and senses room temperature at the thermostat. The wall-mount thermostat has a liquid-filled sensor, connected through a capillary tube to billows with an internal plunger that opens or closes the radiator valve. At rough-in, before drywall, a 1/2-inch conduit is installed between the thermostat location and the radiator valve. The radiator valve can then be installed out of site, behind the finish wall, accessible only for service. The billows/plunger is pushed through the conduit from the thermostat wall hole to the thermostatic radiator valve. Capillary tubes come in various lengths — 6½, 16, and 33 feet. The 16-foot length capillary tube remote thermostats are the most popular; any excess capillary tube can be wound behind the thermostat.
Some manufacturers of wall-hung style panel radiators have the added benefit of an integrated thermostatic valve. The thermostatic operator can then be added directly to the panel radiator. Supply and return can be piped to the panel radiator at the bottom tappings with panel radiator adapters. The supply and return single valve adapters are cast in either straight pattern configuration (for piping from the floor) or angle pattern for piping from a wall. These adapters may be used as isolation valves and drains for removal and service of the panel radiator. For series-loop systems, a unique panel radiator diverter valve adapter allows for flow bypass to the next radiator in the loop.
A/C control options
Thermostatic radiator valves are adaptable for an A/C control option. They can be installed with an on/off electric actuation or a proportional electric actuator. When standard 24VAC wiring is desired and central controls are necessary, actuators can substitute for the typical non-electric operator. In fact, some codes require setback thermostats. In California to meet Title 24, a 24VAC actuator would open and close the thermostatic radiator valve for a setback thermostat or a central controller.
Piping for optimal performance
Although there are many methods for piping panel-style radiators into a hydronic heating system, a favored approach is installing home-run distribution where each panel radiator has its own thermostatic radiator valve. With home run distribution, temperatures are delivered to each radiator equally and the thermostatic radiator valve regulates flow through the emitter to balance room temperature. For this piping detail, each radiator has its own supply-and-return tube originating from a manifold station. There may be up to 12 loops, or panel radiators, per manifold station. In some cases, there may be several manifold stations for each level of a large building. Low flow rates for each panel radiator require small diameter tubing (no larger than ½ inch) for supply and return from each manifold station.
Panel radiation with home-run distribution works perfectly with energy-saving features that are key to green design. First is the use of outdoor reset. Energy savings of up to 35% can be realized. The temperature of the supply water delivered to the emitter is adjusted to changes in outdoor temperature. Therefore, during mild outdoor temperatures, a fully condensing boiler may require very low temperatures, keeping efficiency high at the boiler. The lower water temperatures delivered during mild days or nights saves energy over high temperature delivery throughout an entire heating season. The use of variable-drive circulators is another energy saver, this time for electrical consumption at the pump. With hydronic systems that have constant changes in pressure and flow, these “smart pumps” sense pressure drops or differential temperatures as the actuators open and close or as thermostatic radiator valves modulate flow. The response at the “smart pump” is to increase or decrease the speed at the pump. With this approach, there is no need for a differential bypass valve and full power at the circulator. The green add-on that designers like is the additional energy savings at the pump.
In Europe, where fuel costs are at a premium, hydronic heating by panel radiation is very common. The need for fuel efficiency and the desire for luxurious warmth drive the market for hydronic heating in Europe. These same market forces are at work in the United States, as incremental efficiencies for energy savings are being sought after. Therefore, it’s understandable that the market for panel radiation with the use of thermostatic radiator valves will continue to come of age for commercial buildings in today’s greening U.S. economy and into the 21st century.
Peter Biondo is technical sales coordinator of Oventrop Corporation. He has been involved in solar energy and energy efficient hydronic applications for more than 25 years. Mr. Biondo is a Webinar instructor for the Radiant Panel Association. He is an instructor at Solar Energy International and at North Carolina State University. His solar domestic hot water and space heating workshops are held in trade shows throughout the country. His primary work is assisting mechanical engineers and contractors involved with Oventrop solar heating systems for residential and commercial applications. You can reach him at peter.biondo@oventrop.com.