Let me take a few minutes to describe the fish room and the surrounding environment. The room itself is 12x17 with a slanted ceiling facing south. The ceiling height varies from 10' on the south side to about 20' on the north side. The fish room is considered exterior to the rest of the house, and by that I mean the shared walls are sheathed and insulated as a normal exterior wall would be. This room is also outside the house's HVAC envelope.
While the rest of the house has a basement, the fish room does not. It has supports driven all the way to bedrock, and is made of 10 inches of reinforced concrete. The floor is sloped to a 3" drain which is centered in the back of the room. We are on a well and septic system, and I didn't want to dispose of all the saltwater in to the main septic for fear the salt would build up over time and cause problems with the bacteria and septic function. So, the drain in the fish room has its own underground gravel pit.
The room is designed to contain all the water in the system in the event of a disaster. The floor is 18" below the level of the main floor of the house, and there is a rubber EPDM seal between floor and the walls. Though I really, really hope this isn't needed, the design goal here it to be able to contain the full amount of all water in the system within the fish room, and prevent it from entering the main house while the floor drain does its thing. I can't even imagine a scenario where the tank, both sumps, refugium, and surger all blowup at the same time, but better to be safe than sorry.
My Pop (now retired) worked for many years at the Department of Energy's Residential Research and Standards division. Because of that I was blessed to have many talented and knowledgeable folks work on the house's energy design. The house is heated and cooled by a Geothermal unit, and I really wanted to use that for the tank as well. However, it seems to me the residential Geo unit doesn't have the precision I am looking for in temp control, and it would be an awful headache for one unit to serve two very different functions. In the end, I feel the Geo unit will provide for the comfort of my family, but isn't suitable for a critical life support system.
So, the fish room was excluded from the house's HVAC envelope. However, we did make some important concessions. The house is fairly tight (0.42 ACH), and because of this we import fresh air for 20 minutes out of every hour. The only way out for this fresh air is through a duct in to the fish room, and then out through an exhaust fan. The exhaust fan in the fish room is controlled by the HVAC's fresh air system, and helps pull fresh air through the house out through the fish room. This means the house is positive pressure compared to the fish room, and keeps any funky smells from coming in to the house. The airflow is directed to sweep the skylights and reduce the chance of forming condensation. This also imparts a heating or cooling effect to the fish room without directly impacting the energy performance of the house. Additionally, this is the only means for humidity control. I am a little concerned that there is no humidistat; instead this control is only based on time. I do intend to keep the tank well covered. So hopefully this won't be an issue.
One of our early hopes was to make the entire house a net zero house (generate as much energy as it consumes). In the end, it just wasn't a feasible thing to do, but every aspect of energy usage was considered. That same philosophy was brought to the tank design. Although tempered with a heavy dose of reality. Someone earlier in this thread asked about solar panels to offset the energy use of the tank; solar cells weren't dismissed lightly. We went through several design iterations to try to incorporate them, but financial reality squashed it.
Well.. that was a heck of a long post.. sorry for any glazed eyes out there.
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It's hard to see in the first pics, but the overflow is coast to coast - 93.5 inches.
