Douglas County Jail


Douglas County Jail Install
Solar Heat Exchange Manufacturing was tasked with installing a solar hot water
system at the Douglas County Jail in Lawrence, KS. The system was installed to augment two 100 gallon boilers in the basement mechanical room at the jail. These boilers supplied only part of the buildings hot water supply. Five Solene Aurora 4’x10’ collectors were connected to a SHEM 120DB, a 120 gallon solar hot water tank manufactured by Solar Heat Exchange Manufacturing.

The initial site evaluation was conducted several months before the installation. Building plans were examined to determine the best location to place the solar collectors. The original location of the collectors was to be mounted to the wall over a utility pit next to the building. Immediately prior to installation, it was discoverd that the compass rose on the building plans was mislabeled, not accurately showing south. The collectors had to be moved to a different location one day before their installation. Changes to racking were quickly made to accomodate ground mount, verses originally planed building mount. (See Forum, Commercial Installation Guide for racking diagrams for ground mounted collectors.)

Before the installation was to begin, a one line plumbing diagram was drawn up. Since the collectors must sit on concrete piers poured into the ground, Dig Safe (dial 811) was contacted and the underground utilities were properly marked. This service is free in all states. Allow for 2 days for this process to occur prior to any digging.

The angle iron holding the collectors had to be designed with a slope of at least ¼” per foot to allow for adequate draining of the collectors. The frame also has to be strong enough to resist wind loading.

Installation
To begin the installation, the cold water supply to the tanks was shut off and the gate valve and two diverters were installed to run the cold water to the heat exchanger. Copper piping was hung from the ceiling using pear pipe hangers running between the gate valve location and the heat exchanger. All of the piping running between the gate valve and the heat exchanger is ¾” copper piping. A dial thermometer was installed on the heat exchanger out so the temperature of the water pre-feeding the existing boilers can be monitored. A 3” hole was drilled in the concrete wall between the tank and where the collectors were going to go.

Originally the collectors were supposed to be mounted to the side of the building itself, sitting 7’ off the ground at the lowest point and sloping at 40° towards the building. Mounting them to the wall was ideal because a concrete ledge surrounding an air handling pit provided a stable mounting point at the low end of the collector while the building itself provided the high end mounting. The building plans showed south pointing perpendicular from the wall where the collectors were going to be mounted, but later the compass rose proved to be incorrect and that location lost its sun coverage at about 2:00 in the afternoon in early June. So the collectors had to be moved out about 30’ from the building and rotated 45° so that they would face south. This added a lot of work to the project. A 20’ long by 24” deep trench had to be dug for the piping to the collector to be run through. Eight 3’ deep by 8” diameter piers were augured and poured to provide a good enough footing for the collectors.

The trench was dug by hand because the law states that any digging done within two feet of marked utilities must be done in this manner. And since the trench ran right next to a power box, it had to be dug by hand.

The end of the trench closest to the building was dug to a depth of around 28” and the end closest to collectors was around 14”. This provided a slope of greater than ¼” per foot to allow for good drainback. Once the ditch was dug, sand was poured into the trench and graded to provide the drainback slope. Copper pipe was laid side by side in the trench and sweated together. Once it was sweated, Armacell (closed cell pipe insulation) was put around the pipe. A U channel “lid” was created out of pink foam board insulation. This provided a barrier from moisture coming from above and provided a little bit of structural support on top of the copper. The temperature sensor wire was laid on top in between the copper pipes so that the foam U channel lid sat over the wire and protected it from the environment. At the places where the copper pipe penetrated the ground, left over short pieces of concrete form tubes were set around the pipe to a depth of 5-6” underground and concrete was poured in this tube to protect the tubing from lawnmowers and weed eaters.

Ultimately, the buried collector loop design proved faulty. Pipes in the concrete wall froze, and collectors were ruined and replaced. To cure this defect in the future, a 10% anti-freeze glycol mix was added to the tank.

Conclusion
The installation overall was a success, but several changes would be made if
this project were to be done again. The feet on at least the lower half of the frameshould be rotated 90° so that they clear the angle iron and can be accessed more easily.

In the future a big concrete pad poured under the collector might be better than augering holes. A pad might be easier to construct since a well constructed pad islevel by its very nature. This means that mounting the frame to the pad might beeasier, and there is no need to worry about mulching or cutting the grass under the collectors.

At this location the sun is blocked in the evening so the collector array mighthave benefited from being rotated 5-15° to the east so that it can take advantage ofmorning sun more than it does right now. Click here for this information and additional analysis

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