Landscape Architect Articles

Sub-Surface Assists03-01-16 | Feature

Sub-Surface Assists

Installing heating and cooling elements underneath pavers is an excellent add-on service to present to customers where frigid winters render driveways, walkways and patios dangerously slippery and sometimes impassable, or blistering summers make walking on paved areas uncomfortable, and possibly painful.

Here, LC/DBM presents three examples of this type of work to point out the varied options, and provide guidance on installation procedures.

A ThermaPANEL system from Therma-HEXX, which is a sub-surface system that collects solar heat from pavement, not only provides 100 percent of the heat to warm the two pools and a spa at Gateway Canyons Resort in western Colorado, it has also cooled the pavers down from 185 degrees to 125 degrees.
Photo: DTJ Design, Inc.

Heating Up While Cooling Down
When Gateway Canyons Resort in Gateway, Colorado wanted to switch to a solar heating system to warm their two pools and a spa, the plans called for thermal solar collectors on top of the carports in the parking area. They chose Cloward H2O of Provo, Utah as the water and pool engineering company to give them a hand.

Cloward suggested they instead opt for the ThermaPANEL system from Therma-HEXX, a sub-surface system that collects solar heat from the patios to provide 24 hour heating of the pools from the retained energy in the thermal mass of the pavers, cool those pavers during the heat of the day, and eliminate the need to install screening to hide roof-based solar collectors.

Landscape architect Greg White of DTJ Design in Boulder, Colorado designed the project and FCI Constructors of Grand Junction, Colorado supervised the build. Since it was a ground mounted installation, it required an ICPI approved sub-base, with a thin layer of sand on top of the base to fill any voids in the rough base material.

Therma-HEXX installed the solar thermal system, which consisted of 2,000 1.4-inch-thick solar panels with one-inch-thick, three pound density EPS foam insulation mounted to the back of them. The panels are factory connected in rows up to 50-feet-long, and then folded into 6-foot-long boxes for shipping.

At the job site, the bundles were set out at one end, unfolded into place, and then hooked up to send/return manifolds with polyethylene raised temperature (PE-RT) tubing row by row until the entire zone was connected and pressure tested.

Then the hardscape installer, Rocky Mountain Hardscapes of Denver, applied one inch of bedding sand and tamped it into the voids. The manufacturer advises using a vibraplate with a plastic base or a hand tamp. After pre-compacting the sand, it was then screeded to the correct depth. The panels provide structure to the base and add full support to the paver array: 10,000 square feet of 3-inch-thick segmented pavers, which were set and compacted as usual.

In the end, the two pools and spa are each on their own heating system. It was conservatively projected that the system would provide 60 percent of their yearly heating requirements. After two years in operation, it reportedly provides 100 percent, to the point that because the supplemental heaters never came on, the maintenance people had to test them to make sure they still worked.

The pavers retain enough energy in the evening to keep the pools and spa up to their designated temperatures 24 hours a day in warm-weather months, and above freezing in the winter. The system is also capable of assisting with melting snow as water heated by the dormant boilers could be pumped through the panels to clear the patio area.

But maybe just as importantly, in the summer when the days can reach 105 degrees and heat the pavers to 185 degrees, the actions of the system cool the pavers to a safe temperature level.

Over 20 years of foot traffic, frigid winters, heavy use of snow removal equipment and salting had damaged the 7,000-square-foot plaza at the Dakota County Western Service Center in Apple Valley, Minn., a suburb of Minneapolis. Renovation plans included an in-slab, glycol heating system to help provide pedestrian safety and reduce maintenance time and costs.
Photo: Ben Hartberg, PLA, Calyx Design Group

Back in Good Standing
Formerly a source of civic pride, the plaza at a county government building in Apple Valley, Minnesota, a southeast suburb of Minneapolis/St. Paul, had lost that designation thanks to years of pedestrian wear, harsh weather, and the required maintenance by snow removal equipment and heavy salting. Dakota County officials decided to repair its reputation.

As the entrance to the Western Service Center, which houses a library, courts, county engineering department and more, the 7,000-square-foot plaza was re-envisioned as a space that would not only enhance the building's character and serve as a public gathering place, but would require less maintenance.

To address the third goal and to help provide pedestrian safety, an in-slab, glycol heating system became a component of the design: a highly collaborative effort between the Dakota County project manager Josh Kinney, PLA, and the project landscape architect, Ben Hartberg, PLA, of Calyx Design Group. Joel Dunning, AIA, and Pat Jansen, PE, of Wold Architects and Engineers, provided electrical & mechanical engineering as well as overall construction administration. Besides a plaza made with bands of concrete with integral color, the design called for an amphitheater, seat walls, bicycle parking, LED lighting and raised plant beds.

The construction team included general contractor and concrete finisher Morcon Construction Company with Jason Preusser serving as project manager, and subcontractors Kamish Excavating Inc., Wenzel HVAC Inc., and A&J Electric Company. Plant Pros Inc. was the landscape contractor.

Demolition of the old plaza was done with a John Deere 225D excavator with a hydraulic hammer to break up the six-inch reinforced concrete. Ground preparation included digging seven-foot-deep footings for the amphitheater and seat walls. A mini-excavator handled prep work for drain trenches. The subgrade was compacted and eight inches of aggregate was added to make the base ready for installation of the heating system.

"The mechanical engineer designed a system that would utilize return water from the building's central heating plant to pre-heat the glycol tank," states Hartberg. "Then a heat exchanger would boost the system temperature as it's pumped through the nearly five miles of tubing under the concrete."

To construct the system, four-foot by eight-foot sheets of two-inch-thick???(R)???AE'?N????e'?N,A+extruded polystyrene were???(R)???AE'?N????e'?N,A+laid down end to end, followed by a layer of woven wire mesh.

"This was designed so if the polystyrene separated from the concrete during curing, the wire would keep the tubing tight to the bottom of the slabs," Hartberg relates.

The radiant heat tubing was then positioned over the wire mesh and fastened to it with foamboard staples. Next, a #4 rebar grid was built, suspended over the tubing so as to end up centered in the five-inch-thick slab.

In addition, the two 50-foot-long trench drains to intercept runoff were installed.

"(They) were worked into the design to become an amenity, rather than utilitarian," reports Hartberg. "These heavy-duty drains are unique, as the tubing runs under the drains, keeping them flowing in sub-zero temperatures."

Throughout the installation, the tubing was pressurized to endure foot traffic during the multiple concrete pours, and to alert construction crews to leaks, even pinhole sized ones, which could be heard before the concrete was poured, and then seen after the pour.

Before that happened, concrete formwork was set up around the rebar and tubing. The colored bands of concrete were put down first, followed by the sidewalk infill after the outer bands had set. The form-liner seat walls, amphitheater, lighting and landscaping were then installed. As a final touch, a local artist was commissioned to sandblast a relief of the geographical boundary of Dakota County into the plaza, which was then painted with black epoxy, mirroring a mural above the door.

The overall project timeline was five months from start to finish and the transformation of the space is nothing less than dramatic according to many Dakota County staff. When the snow makes an arrival, the heating system is triggered by moisture sensors in the plaza area.

Hartberg sums up, "The introduction of the many colors, vertical elements, pedestrian access and safety, and reduced maintenance hit all of the project goals, and the space is set to welcome users for many years to come."

When residents at this house on Long Island in New York wanted a new paver driveway, walkway and steps installed along with a heating system to keep them clear of snow and ice, landscape contractors OutdoorLivingFX opted for an electrical system composed of mats available in widths of 2' and 3', and lengths between 5' and 60'.
Photo: Madison Paige

No Shoveling Required
In Miller Place, New York, customers of OutdoorLivingFX wanted more than just a new walkway, steps and stoop. They desired them to be maintenance-free in the winter and Jeffrey Ingrassia and his team were only too willing to help them get that.

The solution selected in this case was an electrical system composed of mesh mats with twin conductor heating cables taped on to them in a serpentine pattern equally spaced three inches apart. The rolled-up mats come in widths of two feet and three feet and in lengths between five and 60 feet. Once installed, they are connected to moisture and temperature sensing controllers.

The manufacturer states that their product is not difficult to design for and relatively less expensive to purchase and install. That said, Ingrassia admits there were a number of challenges.

To prep the install, the OutdoorLivingFX crew demoed the old brick walkway and concrete and block stoop with the help of a skid steer and jack hammer. After compacting the soil, a four-inch base of concrete with wire mesh was poured.

Two 25-foot-long, two-foot-wide mats were rolled out and a 1/2-inch layer of sand was placed on top to help secure them. The 2 ???(R)???AE????-inch-thick pavers in a variety of lengths and widths were installed and then bonded with Alliance polymeric sand. The steps and stoop required about 125 feet of loose heating cable provided by the same manufacturer as the mats. All the leads were then wired to an outdoor controller that automatically activates the system based on readings from its temperature and moisture sensor.

As straightforward as the install seemed, Ingrassia was quick to offer some caveats. These included:

An extensive amount of planning the coverage, layout and amperage was vital to the successful install.

Since it is recommended to not test the elements for prolonged periods during or after the install, getting it right the first time is essential.

Utmost attention needs to be given to prevent crossing any wires, which could cause the heating element to quickly burn out once it's activated.

Caution needs to be exercised while cutting pavers so as not to cut the element wires as well.

Some of the challenges on this project that had to be overcome included:

Their electrician had to upgrade the panel (when the project expanded to include the driveway the following year) to handle the increase of amperage needed. Also, he had to install an expensive diverter that allows only one of three zones on the driveway to function at a time: rotating the zones for continued coverage.

During the install, the heating elements were left exposed several evenings, which caused concerns of vandalism. Each day the crew did a continuity test to make sure nobody cut the electric matting. If cut, the series would immediately burn out.

The hardest challenge according to Ingrassia is that the final test couldn't be conducted until a cold, snowy day happened, and working on any problems in those weather conditions would have been difficult.

As it turned out, no problems occurred.

"With heated matting, we gave them a gift that keeps giving: never having to shovel again," enthuses Ingrassia.

And as mentioned, the customers were so pleased that they hired his company to install a new heated paver driveway, which has already been completed.

"We have been successful on these projects and sold one to a neighbor for her renovation starting in two months," Ingrassia says, then adds, "Bear in mind this improvement could make or break your reputation in the industry."