I'm building a new home in central PA, it is a ranch with a full finished walkout basement. 2200 sq ft first floor, 1700 sq ft finished basement. We are doing geo, selected WaterFurnace 7 series, and are leaning open loop (if well works out right). WF GeoPro dealer did full calc for the house and came up with a little over 4 ton load, so we are doing the 5 ton WF 7 series.

My question is regarding the open loop configuration we are hoping to utilize. I teetered back and forth over closed/open loops, but there is lots of water here, and I need an irrigation well for sprinklers, so I thought killing two birds with one stone would help. Cost savings of just having to do two wells versus three wells (and taking into account the deeper wells and extra cost of closed loop install) was about $11k. My only hesitation is I know you have to take into consideration the operational costs of the well pump. That's what I need help with.

The supply well is drilled 180' deep, provides almost 100 GPM, and the pump would be set at 100' with static water level at 40'. Well is about 100' from the house too.

My needs are this: Irrigation needs 48 psi and 12 GPM. The WF 7 I've been told needs about 15 GPM at only about 10 psi, but I've also seen that you only need 1.5-2 GPM/ton for open loop? Anyone able to help? Does the WF7 need 3 GPM/ton?

Either way, I need normally 10-15 GPM only at 10 psi, and for a couple months of the summer, for a few hours a day, I need an extra 12 GPM and pressure of about 50 psi.

Geo dealer only cares about his water, so this part has fallen back on well provider. That's why I need advice. He recommends a 2-tank, VFD setup as follows:

Gould's pump (2 hP or 3 hP)
Franklin Electric Motor - 3 phase, 230 V
Pentek Intellidrive VFD
2 small bladder tanks, PIT, and FS, and leak sensor

Basic operation would be pumping through 1st bladder tank to a setpoint of 10 psi for geo, thus reducing power consumption of VFD and saving operational cost. Whenever irrigation is called for, and flow past FS exceeds 1.5 GPM, the Pentek would kick up to setpoint of 50 psi. There would be a check valve then another bladder tank and the FS on the line to the irrigation system.

My main questions are:

1) How much water does my WF7 need for a 5 ton?

2) Will the two pressure setup help to keep operating costs reasonable? Or is there another option that is better?

3) Will the WF7 be able to handle dual pressure feeds? 10 psi and then 50 psi periodically? I'm assuming the flow control valve will just respond accordingly during higher pressure periods right?

4) Main question: Any input on size pump to get? 2 hP looks to be borderline, especially if we'd draw down to close the 100' level, if at the same time at peak water demand, but on the other hand I'd hate to oversize and jump to the 3 hP without good reason.

Advice is appreciated!! Thanks in advance.

OK, this has been said before. When you go to build a new home in a heating climate, you really ought to put your first money into building a very highly insulated (superinsulated) and tight home, with excellent windows selected to avoid unnecessary thermal gain on the west and east sides, and mechanical ventilation for interior moisture control in winter and for occupant comfort. Do this before thinking about how to throw cheap heat into it, and you will have a home that is much more comfortable in winter and summer. A properly sized heating/cooling system for such a home will be smaller, whatever it is, and thus less costly to install and operate. This is particularly true of GSHP systems, where installed and operating costs are directly related to tonnage.

For the house size you describe, the GSHP system size you mention (4 ton) probably is about right for "ordinary" construction, built just to meet code. But for perhaps 5% more in construction cost you could have a superinsulated house of the same size that will be kept comfortable year round with just a two-ton system, running in first stage only, below full capacity. I know this, because my own home in central NH, climate zone 6 (you probably are in CZ 5), has 2000 sqft on the upper level and another 2000 of conditioned space on the lower level, set into a hill, so is half walk-out. It is heated by a two-ton GSHP, standing column well (SCW) design, and keeps things at temperature without having to upstage or use electric strip supplemental heating, even when outside night temperature goes below zero. It's been in operation for about six years. The only failure to date has been the water flow valve, recently replaced. I do replace the MERV11 air filter now and then, so it's not totally maintenance-free.

For more information on what's involved in building a proper structure for your location, go to greenbuildingadvisor.com and search on "pretty good house." As they say, this isn't rocket science, but it is building science. And it's very well understood now. But you have to do your homework, a lot of reading, to get what you want. Most builders don't know how yet, but many are willing to work with you to give you what you want and learn how in the process. It worked for me, but I knew what had to be done.

Thanks for the feedback. Actually the house is fairly well insulated and sealed. Not ICF good, but pretty good. We did spray foam for the rim joists, the cathedral ceiling and flat ceilings, with cellulose used to bring the total up to R49 above those flat ceilings in the attic (flash and batt). We also put taped foam board on exterior walls, but chose for the standard batt insulation for the interior of these vertical exterior walls. So while not a perfect insulation job, I'm thinking it's a pretty darn good balance of cost/benefit. Even with that though the WF rep came up with 4+ ton sizing, but I'm thinking that doesn't sound super crazy. It is a WF 7 with variable speed though, so it can ramp way back as needed. I've been told it's hard to oversize them, though obviously spare capacity that's never, ever used should be avoided. We don't have the actual equipment purchased yet, but the ductwork is installed and was sized with the WF 7 in mind (5 zones), so if someone can help chime in on my other questions it would be appreciated. Thanks!

What is the diameter of your well?

The reason I ask is to see if it would be possible to install a 4" submersible pump for your geothermal heat pump, then have a 2-line deep well jet pump installed at the surface for irrigation purposes.  The jet pump would need two pipes plus a foot valve dropped down the well alongside the discharge pipe for the submersible pump. It would be hard to get all of this down a 4" well, but should be possible with a 5" or 6" well.  Set the submersible pump at 100' or more deep, then set the jet pump foot valve at 60' or so assuming your static water level is -40' all the time.

For the heat pump, you only need 1.5 to 2.0 gpm of open loop flow per ton of load.  If you only have 4 tons of peak load with a 5 ton variable speed heat pump, you really only need the water capacity for 4 tons.  Regardless, a 10 gpm capacity pump would be more than sufficient.  And you don't need to have it pump at 10 psi.  Just have the well pump start when demanded by the heat pump with no intentional pressure restriction.  Although, if the heat pump is capable of operating a modulating water valve, installation of such a valve downstream from the heat pump would reduce water consumption and save pumping energy, especially during part load conditions.  Given the water level is 40' down and due to friction losses in the pipe and heat exchanger, you would need a pump that can move 10 gpm against at least 60 ft of head to be on the conservative side.  You can move this amount of water with a 1/2HP submersible well pump.

Check out these example pump curves - for your application look at the the 10 GPM 1/2 HP pump curves.  This example shows 13 GPM capacity against 100 ft total head which exceeds your needs for the heat pump.

http://www.sta-rite.com/Residential...1.aspx

For the irrigation pump, you should be able to meet that need with a 1 HP 2-line deep well jet pump.  Have it set up with pressure tank and pressure switch with a 40-60 psi set point.

This pumping arrangement should save you considerable $ on installation and operation over what was proposed using high HP VFD pumps.

Also, could you use your heat pump water discharge for irrigation?  What are you trying to irrigate?  Could you use a sub-surface drip irrigation system supplied at low pressure by the heat pump waste discharge and then supplement as needed with the top side irrigation pump?

Another option would be to bury a 1000 gallon tank (such as a common concrete or plastic septic tank) with a 3/4 HP shallow well pump setting on top to take suction from the tank and provide for irrigation.  The tank would be filled by discharge from your heat pump waste water stream.  A control scheme could set up using a float switch in the tank to keep the tank full using the submersible pump to pump through the heat pump heat exhanger regardless if the heat pump is running or not.  Once the tank was full the submersible pump would shut off unless the heat pump was running and needing water flow.  You would need to have a means to dump the excess water from the tank when heat pump demand is high, but irrigation demand is low.  Another better option would be to have an electric solenoid valve on the water supply to the heat pump and a second supply to the water tank.  The heat pump would have priority and have flow through it and discharge to the tank.  When the heat pump was not running, but the tank needed filling, the solenoid valve to the heat pump would close and the solenoid valve to the tank would open.  This would result in more rapid fill of the tank and less erosion of the heat pump heat exchanger.

I agree with arkie6. There are better ways to skin this cat than a VFD system. But the pump man is not going to know how to do the math. His only math will be to see how much he will make on the VFD system, which is why the VFD is HIS number one choice.

After doing the math, a 3HP can only be slowed down to a 1HP load for the heat pump. A 2HP can only be slowed to a little over 1/2HP load. But a regular 1/3HP, 10 GPM submersible will do 15 GPM at 80' of head. Depending on your energy cost, this could save 30+ bucks a month over the VFD system. Not to mention the difference in up front equipment cost and long term maintenance.

If you have room for a 1000 gallon storage tank, you can let the heat pump discharge into the storage tank. If you can keep this tank above ground the overflow from this tank can be the discharge rate and source. That way the 1000 gallon tank always stays full without any float switches or controls of any kind. A small jet pump attached to the bottom of this tank can supply 50 PSI to the house and sprinklers when needed.

The 1/3HP submersible would supply the heat pump with the least amount of pumping cost. If you can match the heat pump demand with the 1/3HP pump, you would only need a small pressure tank and pressure switch at maybe a 10/30 setting. This would greatly reduce the cost and simplify the controls compared to a VFD system.

Not only would the standard single phase 1/3HP pump system cost considerably less and use less energy, but it will last 4 times longer than any VFD system. I have been doing this for many decades and I hear from lots of people. Most tell me their VFD systems save some energy, but the continued replacement cost for the VFD and the pump cost more than it saves in energy. With an open loop heat pump saving energy for pumping is important, but not as important as a long lasting pump system that won't cost more for repairs than it is saving in energy.

Note that the most important point for open vs closed loop is water quality. And if you go open loop, monitor the pressure drop and set it up so it is easy to acid clean the heat exchanger. Hardness deposits form mostly from use for cooling (AC).

I'm not aware of any reason that you can't use a single well (vs 2 or 3).

There is lower risk and higher comfort & resilience in Dick Russell's approach- spend the real money on going way-better than code on the building envelope, which allows you to skimp on the mechanicals.

A 4 ton load for a 2200' house + 1700' walk-out basement sounds like code-min (or less) construction &/or a not very careful or aggressive load calculation (likely).

Mini splits are coming out this year that has 40 SEER rating..