Dog Day Afternoons: Dog Park’s Solar-powered Restroom Goes Off-grid
By John Mesenbrink
When Heritage Park, a 1,238-acre park located in Johnson County, (Olathe), Kansas, needed to go a little “off-grid,” a top-notch solar photovoltaic (PV), hot water and radiant floor system — a complete solar-powered restroom facility — was the answer. In particular, the off-leash dog park needed an oasis of the human kind. To accommodate the 200-plus person per day traffic, a state-of-the-art, off-grid restroom was designed, built and is now in full working order. This 30-acre, fenced open space park with a small pond is a playland for hundreds of canines — and happy humans — to roam free.
Architect Berger Devine Yaeger (BDY), who spec’d the system, was approached by the Johnson County Parks District to design a simple restroom structure in the dog park that could be used year-round. Because of its location, off-grid was chosen for energy design. The building features both solar thermal and solar PV systems to facilitate the off-grid application. This simple restroom became a cost-efficient, energy efficient, green building by utilizing the following:
• Photovoltaic source of electrical power;
• In-slab radiant heat with rooftop solar vacuum heating tubes;
• Passive solar heating by the use of a Trombe wall;
• Indirect lighting through the use of clearstory windows;
• Durable cfmu insulated masonry wall construction; and
• Structurally-insulated roof panels.
The contractor for the solar thermal job was Bob Dolan, owner, BMK Plumbing & Solar of the Midwest, who won the contract to install waste, vents, water, radiant floor heating, solar thermal and solar PV.
The solar thermal system consists of 120 Viessmann Vitosol-300 evacuated tubes supplied to BMK Plumbing from Metropolitan Industries, Romeoville, Ill. There are a total of four, 30-tube manifolds. The solar thermal tubes are used for heating the floor, which, of course, has radiant tubing installed in it.
The Vitosol 300-T high performance vacuum tube collector operates according to the proven heat pipe principle. It offers particularly high operational reliability. One of the specific applications of the Vitosol 300-T is in systems with long phases of high solar irradiation without heat transfer (so called stagnation phases). The dry connection of the heat pipe tubes inside the header and the integral temperature limiter ensure particularly high operational reliability.
In heat pipe systems, the solar medium does not flow directly through the collector tube. Instead, a process medium, which circulates in the copper pipe below the absorber, evaporates when subjected to solar irradiation and transfers the heat to the solar medium via a heat exchanger.
The condensers are completely surrounded by patented Duotec twin-pipe heat exchangers. This absorbs the heat particularly well and passes it into the heat transfer medium flowing past it. Also, a temperature limiter integrated into the Vitosol 300-T protects the system against overheating during longer idle periods.
The system also used a Viessmann Divicon pumping station and a solar controller.
The hot water storage tank is a 400-gallon solar tank custom-built by Metropolitan Industries and has double coils for transferring heat from the solar system to the radiant floor system. The tank is well insulated with 3" foam on the top and 2" on the sides.
A 150-gallon propane tank was used as a back-up heating source.
The solar PV system — consisting of solar modules that convert the sun’s energy into electricity — is made up of 20 Suntech 175-watt PV panels, supplied by Conergy, which charge 24 batteries. Conergy selects the best solar modules in the industry, including selections from BP, Sanyo and GE. The DC power in the batteries is converted to AC power, which runs the lights, fans, solar pumping station and radiant floor pumping station.
“My good friends at Pestinger Heating and Air, Salina, Kansas, who installed the HVAC, electrical and solar PV systems, partnered with me on the electrical and mechanical part of the project,” said Dolan.
The net energy usage is conservatively estimated at 2,347 kw/h and 378 gallons of propane, as estimated by Richard Beardmore, engineer, Latimer Sommers & Associates. (See Figures 1 and 2 for potential thermal and PV savings.) “Since the solar PV and solar thermal systems were designed to carry the loads on sunny days, it’s all savings, but we do have propane as a backup source,” said Beardmore.
“With the uniqueness of the solar thermal and solar PV on this project, the general contractor, Wilcott Construction, took great care in detailing to the architects and engineers all items that came up in the construction process; this resulted in those issues being addressed promptly, keeping the project moving forward. The engineers and architects were very forward thinking as well,” said Dolan.
The project wasn’t without its share of obstacles. Balancing the cost, maintenance, payback and energy usage were just some of the problems to overcome.
Also, BMK battled the elements while working on the project in the winter months. “After a long battle fighting winter weather, the Heritage Park solar-powered restroom is up and running. All that remains now is to allow the sun to do its work to run this facility. Time will be on our side in proving that solar thermal and PV can work on buildings such as this,” said Dolan.