Sunday, February 6, 2011

Wiring Slow Operating Valves on a Geothermal Heat Pump.

With the costs of fuel (any fuel) still heading skyward, the idea of "free" energy from the ground is a reality more and more households are cutting their teeth on. Geothermal systems cost upwards of $7000 to $20000 depending on the features and if this is an open (pump and dump) or a closed loop system. Because closed loop systems require a lot of plumbing run in the ground, these are very expensive, especially for someone changing from another fuel type (In the city, with a municipal water supply you will HAVE to use a closed loop per codes if they even permit a geothermal heat pump at all. This system will dump water in the sewer system if installed open loop). For those in the country or a private well, an open loop or pump and dump makes sense. The cost is relatively low and there's a lot less plumbing to get it going. Pump and dumps use water from the well to either extract or absorb heat from the ground. This is because most groundwater is about 55 degrees and even though it seems cold in the winter, has quite a bit of heat (even frozen water has heat, but would never make it through the system).
This is a pretty simple setup. The heat pump is plumbed into the water supply via pipes with a manual valve on the ingoing side an one or two valves on the outgoing side, depending on whether or not it's single or two stage unit. Two stages will have a straight pipe with a loop attached with a valve on the loop and one on the straightaway. The first stage will always be on the straightaway and the second stage will be on the loop. In theory, the first stage valve will open when the thermostat calls for heat and stay open, even when the thermostat calls for second stage. Simple huh? Otherwise the furnace will shut off on low water flow and the emergency heat will probably come on. Customers hate that.
Now for the disclaimer. I am not responsible for any damage done to your furnace as I am not your boss. You MUST READ the instructions on the valve packaging AND the furnace. Improper wiring or testing methods can cause personal injury and property damage. You MUST determine whether or not this is going to work for your application. Follow any advice at your own risk.
Believe me, I burnt out a control board and a thermostat trying to fix one of these systems and the customer wasn't a happy camper. Shut off the power to the unit before disconnecting or connecting anything and if you must use a voltmeter, please tape the ends so only the very tip is showing. This is so you don't introduce high voltage to a low voltage part or pop a breaker. The geothermal heat pumps I've worked on don't have a fuse for the board (mainly Water Furnace). You've been warned.
Water hammer is the sound made when a valve closes suddenly under high pressure. Copper plumbing seems to be prone to this because there's no give. Because any action will cause a reaction, shutting off a valve quickly will stop the water flow, but not bleed off the energy behind it. This is like a car running into a bridge abutment (hard and sudden) as opposed to having the brakes bleed off the energy in motion (kinetic energy). Slow operating valves limit or eliminate water hammer by opening and closing slowly, bleeding off the energy of the water flow.
But these can be a nightmare to install if you haven't had any instruction on them. Several calls to Water Furnace tech support had me wiring these to the board and contactors, but no dice. The valves didn't open and the furnace wouldn't operate. The written instructions are also unclear on this step and will confound the tech at every turn. Personally, I've no problem with doing the job, but I'm not abreast of the technical jargon either. I've also learned the more complicated you make something, the more likely you are to royally screw it up. Such is the case with this furnace; there was no clear way to wire this beast up.
Or is there? The valves, made by Taco (pronounced Tayco) have orange power heads and three terminals, each marked 1, 2 and 3. There's also a schematic on each valve. Use this schematic to wire them up. Here's how to do it.
What you'll need is enough three or five wire (18 gauge thermostat wire) to reach the valves and the terminals on the board. Three is for single stage and five is for two stage systems. You'll also need three wire nuts for the two stage and none for the single stage.
Take your wire and run it into the furnace and loosely place it where you want it where it's going to away from anything that will damage same. Slit the outer insulation about 8 inches at each end and peel the wires apart as using a stripper on the outer casing will nick the wires. Strip off enough of the inner insulation so you can hook everything up without the bare wires touching each other. Hook the number 1 terminal (s) on the valve (s) to the common or "C" on the board. One wire should suffice for both; use two short pieces and a wire nut to hook up the common wire. Now this is where it gets tricky. Find out which valve is for first stage, hook one end to the number 2 terminal. Hook the other end of this wire to the "Y1" ("Y" if it's a single stage) taken from the board. Then hook another free wire to the 3 terminal on the valve and hook that to the "Y" terminal on the board. Do the same with the stage two valve, using the remaining wires to hook up the 2 terminal to the "Y2" wire from the thermostat and terminal 3 to the "Y2" terminal on the board.
What happens is the thermostat calls for heat, or cooling and sends power to the valve, which opens and sends power to the contactor, which turns the compressor on. Numbers 1 and 2 on the valve actually supply the path to operate the valve, while numbers two and three are connected to a micro switch and no power goes between them. These are known as "dry" contacts for that reason. This wire completes the circuit to the board from the thermostat when valve is finished opening. Viola! it should be pumping heat in no time. Maranatha!

4 comments:

Walter Grace said...

This heat pump ended up having more problems and the homeowner doesn't want me there anymore, at least not without my boss. I'm all for "saving" the world, but not crazy about these geothermal heat pumps in the least. I'll settle for a 10 seer and an 80% furnace. Looks like we've outsmarted ourselves with this high tech stuff.

Geochallenged said...

Walter can you provide the model # of the Taco solenoid valve and an Idea of where to find them.

Geochallenged said...
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Walter Grace said...

That model number is 557 G2 for the one inch valve and and 556 G2 for the 3/4 inch valve. You can purchase them at any supply house, or at http://www.pexuniverse.com/taco-556-g2-geothermal-motor-zone-valve. They're about $170 for the entire valve and about $75 for the powerhead. Hope this helps.