When we bought this house, it had a single well, pump, and pressure tank serving both the geothermal HVAC and the domestic water. The county laid water mains just before we moved in 3 years ago and we finally hooked up to city water this week. When doing research on the geothermal system, I learned that pumping the water up to 70psi, storing it in the tank, and then running it through the GSHP is really killing most of the supposed efficiency benefits of the GSHP. Now that the domestic water no longer needs to be supplied from the well, I'd like to optimize the well setup for the GSHP in order to improve the efficiency and stop spending so much money on the electric to pump the water. Ideally, I'd love to have the GSHP turn the well pump on/off as necessary and eliminate the pressure tank, if this is even possible. To make this more complicated, the well and house were built before there was any sort of code enforcement in the county. There's no record of this well's construction at the county office or in the small amount of paperwork on the house that we were given. I have no idea how deep it's drilled, what the water level is, how deep the pump is set, or even what kind of pump is in there. So, in order to re-design the system to make it as efficient as possible for the GSHP, what questions do I need to find answers to? I'm sure the unknowns about the well are important but what else do I need to find out in order to have enough information to pick the best solution? Thanks!
Your heat pump will have a required flow rate depending on its size: - use that to size a pump - or use that to restrict flow to that flowrate (flow restrictors, ball valves,...) - or just overpump if lazy Typically you put a solenoid valve on the discharge side of the heat pump. A call to the heat pump is intercepted by this solenoid. When the solenoid is fully open and water is flowing through the heat pump, the heat pump signal is passed through and the heat pump is turned on. That's about it, assuming you have the discharge sorted already.
Things I know relevant to what you just said: 1)There's a valve on both sides of the heat pump. The outflow one I know is used to control the flow through the heatpump because it failed not long after we were here and caused the water to run constantly. I'm not sure that the solenoid valve on the inflow side actually ever does anything. 2) There is a flow restrictor in the outflow piping just downstream of the outflow solenoid valve. I've been told it's 3gpm, but that doesn't make any sense given that it's supposedly a 3.5ton heatpump (though that spec isn't verified either)
The solenoid valves do tend to fail after awhile. You need a high pressure one as it has to be able to close at whatever pump pressures you're generating. Or you can start adding things like a pressure reducing valve (which does restrict flow as well) prior to the heat pump. Keep an operating valve on the discharge side of the pump as you always want a column of water inside your unit vs. air. Flow restrictions and such make noise (as you've likely noticed), so a properly sized pump is ideal. Ideal for energy savings as well.
Right, that's the whole reason I want to redesign the system and drop to a pump setup properly matched to the GSHP. I'd like to get the system pressure down below 20psi, get rid of the pressure tank, and have the GHSP (or thermostat) turn the well pump on and off as needed only when the GSHP/thermo calls for water.
Well it is as simple as I've shown. So simple in fact, the cowboy days of geo had a lot of open loop systems going in as no design was required.
I remember the no design required days. I am sure the well can handle just the geo. What to do to control it depends on what the goals are. The area around the Columbus belt way is a geo desert. I could lend a hand. I am about two hours away. Mark
Is the existing well pump a submersible pump? Is it wired 240V (2-pole circuit breaker in the panel)? If you could get a clamp on ammeter around one of the wires at the breaker and get an Amp reading, we could figure out approximately what size pump motor you currently have. 1/2, 3/4, & 1 HP are pretty typical for submersible pumps unless you have to lift the water a very long way. As an alternative, most if not all submersible pumps have a control box with starting capacitor somewhere above grade, typically near the water storage tank, power source, or pressure switch. Open the breaker to the pump, remove the cover from the control box, and tell us what the make and model number is. The control box and starting capacitor should be sized for the specific pump motor and this might be able to be used to figure out what you have in the well. How far down to the water level? If you can run the pump now, run it for at least 15 minutes with a valve wide open, and then check the water level in the well. That can tell us how far you have to lift the water (ft of head) under static and in-service conditions.
What size is your current pump? Changing your pressure switch setting to say, 20/30 would let the current pump operate at a much lower head and shut off almost immediately after your GSHP demand stops. If you monkey around with the pressure switch settings you can achieve a constant run opposed to cycling if the current pump is not to large. This will let you use the life you have left in the existing pump. Eric
Will, How did your design change go? I'm working up a change for a 3 Ton Carrier with Open Loop. The header I designed was a bit noisy, plus the diaphragm solenoids I used are sticking open or shut due to the mud that builds up over time. The water control header is upstream of the Unit since I prefer not having the Unit exposed to water pressure continuously. My Brother controls the water flow at the outlet and claims he has less dirt dropping out of the water when used this way. My Trane Unit has a warning not to expose the internals to greater than 25 psig. Due to this I tend to shy away from pressurizing the newer Carrier unit to well water pressure. I'll be adding a 60 mesh Twist strainer at the water source (suggested by Mark if I remember correctly) to clean the water for the whole house & Geo Unit with an auto blowdown valve (as seen on ebay) to remove collected dirt from the strainer at a time interval that I'll determine with use. I purchased a Taco Sentry Normally Closed ball valve (on ebay) to replace the diaphragm solenoid which will eliminate the internal seat that gets clogged in the current design. I have a military quality pressure switch (from ebay) with Normally Open and Normal Closed contacts that operates at 9 psig increasing which will be used to prevent the Unit Compressor from starting if the ball valve fails to open (no well water). The pressure switch will be on the outlet of the ball & throttle valve and will remain open if the Taco Sentry valve fails to open. The Normally Open contact will be wired into the compressor trip circuit on the Controller Card to prevent the Compressor Relay from operating the Compressor Contactor until the >9 psig well water is present. To start your Well pump when the Geothermal Unit compressor starts, you can add a 220 to to 24 vac transformer to the downstream side of the Compressor start contactor to supply a 24 vac output upon Compressor start, which you can wire to a 24 vac operated 220 vac contactor at the nearest section of your 220 vac supply wires to the Well pump (placed in an electrical box in order to meet code). Remove or jumper around the Well pump start pressure switch so the contactor can directly supply the Well pump. You might be able to find another way to pick off the existing 24 vac signal on the Control Card, but having an independent transformer will ensure you don't drag down the 24 vac control power for your Unit due to normal operation or an electrical fault. I have the part numbers for all components mentioned on my ebay history, and I've used this design for other purposes, so I know it works. Ron
