Which one’s warmer?

BY DR. BIROL KILKIS,

contributing writer

I recall a high school science teacher of mine asking the class a question about heat. The question was this: A 1" wooden rod and a 1" steel pipe were placed outside on a snowy day. “If you were to grab both of these, which one would be warmer?” And, what was the overwhelming answer? “The wooden rod,” responded a near-unanimous group of 17-year-olds.

A condo’s 2nd floor receives radiant in a recent retrofit in Missouri with SubRay and RadiantPEX tubing.

I must admit, I was part of that group. Since those early days I’ve learned a few things about heat transfer. The answer to that question, of course, is the same now as it was then -- both objects are the same temperature. The question wasn’t which one felt warmer, but which one was warmer. The steel felt colder because it was more conductive; that is, it moved energy away from our hands faster than the wooden rod did.

In the world of radiant floor heating, I have found a similar, and growing, misconception. Most misunderstandings center around two main issues: tubing and applications. I have heard people claim copper is more efficient than PEX, or PEX is more efficient than EPDM. Others claim slab applications are the only way to install a radiant system. But what actually is the truth? Is one system or product really the best or more efficient?

To answer this we need to understand how heat is transferred in a radiant floor. We have all heard the phrase “heat moves from hot to cold.” This is true, but it’s more important to understand where the heat is coming from and how it gets into the room.

To help illustrate the mechanics of heat transfer, the following example will be used: a typical 20'520' room has a heating intensity of 25 Btuh/ft2 and a desired room temperature of 70°F. Our calculations show the room will not meet our design heat load if the floor surface temperature is below 80°F.

The floor in this case is a radiant panel, and it is transferring energy into the room because it has an elevated temperature of 80°F (remember, hot moves to cold). Does it matter what the floor covering is? No. Does the floor covering affect the room’s heat loss? No again. The room is going to have a 25 Btuh/ft2 load and must have an 80°F floor surface temperature regardless of the floor covering. The same can be said for the floor construction. We can have a slab, thin slab or a frame floor, and the same requirement holds true: the floor surface temperature needs to be 80°F in order to satisfy the heat loss of 25 Btuh/ft2.

Now, that isn’t to say floor construction or floor coverings are not important -- they are. Floor construction will dictate the path (direction of least thermal resistance) the energy will take from the radiant tubing to the floor surface. Floor coverings are part of the floor construction. They play a part in this directional heat transfer as well as help determine the minimum required fluid temperature.

Remember, heat moves to cold in a very predictable manner. And the greater the temperature change (delta T), the greater the energy movement through a given material. Another way to look at this is, the greater the amount of energy needed and/or the higher the material resistance, the greater the delta T needs to be to transfer the energy through the material.

If we change our floor covering in our example room from carpet to tile, the required energy is still the same, but the conductivity value of the floor covering has changed. We still need an 80°F floor surface temperature, but we can now achieve the require heating intensity with a smaller delta T (a lower supply fluid temperature, assuming the rest of the floor construction has remained the same). Regardless of whether EPDM, PEX or copper is used, the required fluid temperature for any one of these would be reduced when we changed from carpet to tile.

We now know what happens when we change floor coverings. Let’s move on and examine what happens to our design if we change tubing options. More specifically, let’s examine system efficiencies relative to the type of tubing used.

Before we can delve too far into this topic, it’s important to first understand what is involved when we discuss system efficiencies. Efficiency is the ratio of useable energy to total energy provided. This total energy includes not only the energy provided to the room, but also energy lost to miscellaneous sources called back and edge losses (the area below and to the side of our radiant panel).

We’ve already concluded that the room’s heating intensity is the same since the load is dictated by the room construction, not the floor covering. What affects efficiency is the back and edge loss, which is affected by the surface temperature of the radiant piping. The higher the pipe surface temperature, the higher the back and edge loss. If the pipe surface temperature is the same, then the back and edge losses are the same.

There are several tubing options on the market today and each one will call for a slightly different design condition based on the given heating application. Our example room calls for a 25 Btuh/ft2 load and a floor covering of carpet with an 80°F surface temperature requirement. The first thing we need to do is to determine what the required fluid temperature needs to be to properly heat this room. From there we can determine the resulting panel efficiency.

To determine the required fluid temperatures we need to work from the floor covering back to the tubing. In our example room, the required floor surface temperature is 80°F. Taking into account the floor construction has a known conductivity value, the EPDM, PEX and copper piping will have to have the same outside surface temperature in order to maintain the required 80°F floor surface temperature.

Likewise, for the systems to have equal heat output, the tubing skin temperature for EPDM, PEX and copper is, and has to be, the same.

However, equal surface temperatures do not necessarily mean equal supply fluid temperatures. The reason why is directly related to the delta T through the tubing wall. Figure 1 shows various characteristics of four pipes used in radiant floor heating.

A fixed delta T helps us to avoid delivering more or less energy than needed, potentially causing the room to overheat or under heat. This means we need to have the same tubing surface temperature whether we use EPDM, PEX or copper. Same surface temperature indicates the same back and edge loss, meaning the panel efficiencies remain the same, even though the supply fluid temperatures vary.

EPDM does require a slightly higher supply temperature than PEX, but the difference is minimal. Recent incomplete “research” that has positioned EPDM tubing as having 20%, 30% or even 40% less efficiency, simply isn’t true -- these are misconceptions. The reality is that EPDM requires only 5 to 6% higher water temperature than PEX in a typical application.

The bottom line: it’s important to design a radiant system for the components being used and, more importantly, install a system according to that specified design.

So, like the example with the wooden stick and the steel pipe asked by Mr. Webster (my high school science teacher, not the dictionary guy) “Which pipe is warmer in a radiant floor?” The answer -- all pipes are the same temperature.                   

Dr. Birol Kilkis has more than 25 years of professional experience, having served as a member of Watts Radiant’s research and development team, as well as serving on several ASHRAE technical and research committees.

Distribution center heats up with radiant heating

Managing a 50,000-square-foot distribution center requires organization and efficiency. Just ask Dennis Prosperi, one of the owners of Henri Studio, the world’s largest designer and manufacturer of original cast-stone fountains and statuary. The company ships premier garden products all over the world from its distribution center in Wauconda, Illinois.

“The facility serves as the hub of our business, so it must run as efficiently as possible,” said Prosperi. “When designing it, one of our main concerns was finding the right heating system. Research led me to hydronic heating systems. I was very pleased when I learned that it offered everything I needed for our warehouse -- comfort and convenience, safety and cost efficiency.”

Comfort and Convenience: Prosperi says radiant heating offered him the kind of consistent comfort and heat recovery a forced-air system could not provide. “A forced-air system makes no sense in a warehouse with 30-foot high ceilings and numerous windows,” said Prosperi. “You can’t beat the rapid heat recovery in the shipping area where doors open and close constantly.”

Prosperi also appreciates the user-friendly temperature control with radiant floor heating. Eight heating zones provide continuous comfort throughout the warehouse. “In the warehouse, we can adjust the temperature according to traffic flow and concentration of employees,” he said.

Safety: Safety is also an important consideration. Since installing a snow and ice melting system at the front entrance of the warehouse, Prosperi has fewer concerns and also less maintenance. Warehouse employees enjoy ice-free sidewalks without the maintenance costs of snow blowers, front loaders, salt and sand.

Cost Efficiency: Prosperi’s decision to install radiant floor heating was based on considerable forethought and research. To demonstrate the efficiency of a radiant system versus alternative heating systems, Uponor prepared a heat-loss analysis. The preliminary data revealed Prosperi could potentially save about $11,000 annually. Exceeding the estimate, actual energy savings were nearly $19,000. The savings essentially paid for the system in as little as two years.

“Choosing an Uponor radiant heating system was the best decision,” said Prosperi. “I would highly recommend it to anyone.”

Summary of benefits

Comfort and Convenience: The warmth provided by the Uponor radiant floor heating system is noticeable throughout the warehouse. Despite 30-foot ceilings and numerous windows, the warehouse maintains an even temperature. In the shipping area, where doors are opened and closed constantly, there is rapid heat recovery. And since employees feel comfortable and warm, they are more productive.

Safety: Since installing the radiant floor heating and snow and ice melting systems, Prosperi has fewer concerns about the safety of his employees. Warehouse employees can now enjoy sidewalks free from snow and ice.

Cost Efficiency: By choosing a hydronic heating system instead of rooftop units, Henri Studio improved energy efficiency.

As a result, fuel savings for the distribution center were $18,939 in the first year.

Mechanical system information

The distribution center features radiant floor heating and snow and ice melting systems in the warehouse, office and sidewalk. A vapor barrier and foam perimeter insulation was used and Wirsbo hePEX™ plus tubing was placed 12" on center in the office and up to 24" on center in the interior of the warehouse. Four, 500,000- Btuh boilers supply heated water to the network. Eight heating zones, each with an individual thermostat, provide appropriate and flexible temperature control.                   

Maine custom radiant home shelters classic cars in comfort

Custom home building usually means unique requests which often lead to creative problem solving by the plumbing and mechanical contractor. This was certainly the case for Jonathan Eaton, owner of Clearwater Plumbing, of Darmariscotta, Maine. He recently finished a hybrid hydronic heating system for a 15-room home overlooking Booth Bay. The challenge on this job was focused around the garage and the homeowner’s desire to display and work on a portion of his notable collection of classic cars.

Two Biasi oil-fired boilers power the heating system and are controlled by a Taco PC702 2-Stage Outdoor Reset Control plugged into a Taco Expandable Switching Relay to save energy via outdoor reset, boiler staging, boiler rotation, adjustable interstage delay and a domestic hot water demand pump output with switchable priority. The primary pump is a Taco 0010 circulator feeding eleven zones, each with a 007-IFC circulator.

The main living areas of the house are heated using a combination of in-floor radiant, including the basement slab and by Concept panel radiators. The heating system is powered by two Biasi oil-fired boilers controlled by a Taco PC702 2-Stage Outdoor Reset Control. The PC702 plugs directly into a Taco Expandable Switching Relay to provide energy savings via outdoor reset, boiler staging, boiler rotation, adjustable interstage delay and a domestic hot water demand pump output with switchable priority. A Taco 0010 circulator is used as the primary pump feeding a total of eleven zones, each with a 007-IFC circulator.

When Eaton was designing the heating system for the house, it was the owner’s use of his garage that ultimately drove the design and equipment choices. The homeowner likes to spend his free time working on his classic car collection in the garage and showroom. A radiant floor system in the showroom, plus the panel radiation in the garage, made the most sense. The radiant floor provides a comfortable environment in which to display his cars, while the panel radiation allows the homeowner to heat the garage up quickly whenever he decides to work on his latest restoration project.

Since the Taco X-Pump Block provides total isolation between the heat generation side of a hydronic system and its heat delivery side, it was the perfect equipment choice to get the job done. This allowed Eaton to avoid the hassles and extra expense of adding glycol to the entire house. The X-Pump Block, Taco’s latest addition to its Radiant Made Easy product line, is an all-in-one mixing system, combining a variable speed mixing control, a heat source circulator, constant speed circulator and an attached brazed plate heat exchanger.

Eaton used a second X-Pump to provide antifreeze isolation, but this one heats the entryway, mud room and melts snow on the front steps to the house. Eaton also set this X-Pump Block up to control temperature by utilizing its built-in outside reset feature, raising and lowering the temperature of the floor, as needed, in direct proportion to the outside temperature. According to Jonathan Eaton, this feature works remarkably well in reducing high and low inside temperature spikes, especially during more moderate weather situations.

Vanguard Vanex PEX lies underneath hardwood floors in the house and connects to Concept radiator panels in the home’s living areas. Concept radiator panels can be mounted under windows or adjacent to outside walls. Eaton credits Vanguard PEX for “laying down quite well” underneath floors. Upstairs, the master bathroom is also radiant. Eaton installed a seventh radiant zone (the sixth zone is for domestic hot water) for a planned outside in-ground pool that will be heated by a separate pool heater.

Eaton calls the X-Pump Block a “sweet little unit” that made possible the extension of radiant heat in the garage and outdoor entranceway. Without the availability of the X-Pump Block, Eaton said that the controls complexity, heat exchanger sizing and space requirements of constructing two separate isolated heating loops to accomplish the effects achieved by the X-Pump Blocks would not have been reasonable. With just four-pipe connections, “The speed of installation and material cost far outweighs anything I could construct in the field,” Eaton said.

Jonathan Eaton is a big fan of Taco, having used the dependable green products for over 30 years. “I like Taco products. The Taco name on the box makes a big difference. I use Taco because it works.” He also credits Taco and its local manufacturers’ rep. agency, Emerson-Swan, with superb technical help and assistance: “It’s the best in the business.”

Water heaters get the ‘green’ light at Johnson & Wales

On a half-mile stretch of the Narragansett Bay in Rhode Island, student life now thrives where a toxic eyesore festered for more than half a century. Johnson & Wales University’s new Harborside Village student apartments now stand on capped brownfields, a dumping area dating back to Liberty Ship construction during World War II.

Technician Brett Bradford installs a Bradford White gas-fired Combi-Cor water heater at Johnson & Wales University’s new Harborside Village student apartments.

Today the area, though still under development, enhances the school’s unique waterfront campus and proudly demonstrates that blighted areas can be reclaimed. The banks of the Providence River here are once again green.

According to Christopher O. Placco, vice president of facilities management for the university, in the mid-80s Johnson & Wales began acquiring property along the river front because of its natural beauty, and the potential for nearly 100 contiguous acres there. The school tapped its own resources and the private help of some of its trustees. “It’s hard to see it right now, when you gaze at the abandoned railroad tracks and see remnants of the debris and neglect, but it’s really becoming beautiful waterfront property,” added Placco.

 

The university just completed phase one of the Harborside Commons project, with the $25 million Village as crown jewel of the student complex that includes a quadrangle, recreational hall, 12 apartment buildings with a total of 576 beds. The apartments will be available to upperclassmen, providing walking access to the classrooms already onsite, as well as access by bus to the school’s downtown facilities. That’s smart growth.

All things green

In addition to being one of the world’s preeminent culinary, hospitality and business schools, the university is among the nation’s leading conservation-oriented, “green” institutions.

An indication of the school’s passion for all things green is their restoration of 1,500 feet of shoreline wildlife habitat that borders the Harborside Commons area. Helping to make the project possible have been grants, totaling nearly $600,000 from the Natural Resources Conservation Service and the U.S. Environmental Protection Agency. The grants are in addition to the school’s own multimillion-dollar investment.

Their focus on all things green extends into the building shell. One of the key steps they took to assure energy-efficient comfort for students in the Village was the installation of 144 CombiCor water heaters by Bradford White. The high efficiency gas-fired units (also available with oil burners) serve a dual purpose by providing hot water for each apartment’s domestic water system, and also to air handlers for hydro-air space heating.

The school’s engineering team and Capstone Construction, the gc, specified the water heaters, then chose Dedham, Mass.-based Superior Plumbing to do the job. “We sourced the ‘Combis’ and other materials and supplies through our wholesaler, [Lowell, Mass.-based] F. W. Webb, who also gave us some advice on the system designs,” said Andy Camiolo, president of Superior Plumbing, a non-union shop with more that 100 employees that focuses its work chiefly on multi-housing plumbing and mechanical projects. 

“We had 14 weeks to get it all done, just in time for students to move in to the apartments in September,” said John Kelly, jobsite supervisor for Superior.  All of the apartment units are about 1,400 sq. ft. in size and consist of a kitchen, common area, four bedrooms and two bathrooms, each with two sinks, a toilet and shower/tub enclosure.

All-in-one water heater

To meet the space and domestic water needs of the apartments, the combination water heaters were sized at 75 gallons and 75,000 Btus. The power-vented “Combis” they chose (atmospheric-fired units are also available with gas-fired systems) offer the versatility and efficiency of an indirect-fired water heater, but differ in that the domestic water in the tank is heated directly by the integrated combustion system. Water in the tank transfers its heat through a large coil in the tank to the closed-loop fluids that circulate to and from a hydronic air handler in the ductwork. This “hydro-air” application provides all of the space heating for each apartment.

“We’re very impressed with the Combi units,” added Kelly. “We got so much capability with such a small footprint, and space in the apartments was tight. They were also simple to pipe and install.”

Kelly explained that -- with 144 nearly identical systems to install -- he and his crews devised a plan to do a lot of the piping pre-fabrications in a first-floor location in each building. “At each pre-fab station, one guy did all of the water copper pipe work, then the dielectric unions,” he said. “Then we’d move the pre-fabbed piping into position in each of the mechanical areas (see sidebar). Next, we’d slide the water heater in on top of the pan and begin the final piping and venting.

“We then put a backflow preventer on the heat side of each unit, and mixing valves -- set down to 120°F -- on the domestic water side,” he continued. Then they added the expansion tanks, air vents and completed the piping.

Four-inch flue pipe was used for the first and second floor water heaters, rather than the customary three-inch. Kelly said that this was necessary because of the location of each mechanical area.

“The manual calls for a 35-foot maximum with three-inch pipe, and we needed about 45 feet, considering the need for three 90-degree angle bends,” he added. “We did the first and second floor terminations on the building sides.”

Venting of the top floor units was easier. There, Superior crews used the standard three-inch flue pipebecause they were able to vent through the roof with a gooseneck for bug screening.

“Once we had the system down, we were able to completely install 12 units per week,” said Kelly.

The system start-up process involved filling the tanks up, and also the heat side coil. Then they purged the tank, and also the closed-loop space heat system.

“The expansion tanks had to be pumped up to the pressure of the system on the heat side: 15 pounds within the system. The tanks were set at 13 pounds,” he added.

“We were all impressed with how well the start-ups went,” added Camiolo. “But the best moment was learning, when the school opened the apartments to students, that all of the systems worked perfectly.”