So a few years back I took out an old 3 ton Trane heatpump and replaced it with two two ton rheem 14 seer heat pumps. Since then I have dropped my electric bill from $300 a month during peek times to $200 or less. My house was built in 1988 and is 1850 sft located in central VA. These systems have paid for their self's  already. I did the installs and saved a bunch.

Well I rented the house for a few years from family and have since purchased it. I got a VA loan so instead of doing a down payment we had a garage addition installed. Due to the restrictions on zoning I had to attach the garage on the corner of my house instead of the front. So, instead of having an unconditioned garage with a 600sft room over top we ended up with an unconditioned garage with a decent size room on the back attaching it to the house and a big room on top. Our house, once finished, will be around 3000sft. Not what we had intended but oh well. Simple things will be reducing heating and cooling load. I have recently found that the attic insulation over the years has settled to around 3 inches thick. The attic has a plywood floor and is framed with 2x8s 16inches on center. I have installed a ridge vent and soffit vents which were not there in the past. There is also a walkup staircase which only had R11 insulation between under the stairs and the attic. I have ripped the stairs out, replaced it with r30, and raised the stairs when reinstalling. Ultimately, I plan to improve the whole envelope including installing radiant barrier under the roof deck and then R19 under that since the ductwork is in the attic.

For the addition I have built a second double stud interior wall which I plan to seal the outer wall, possible get 1inch flashed with spray foam, and fill with cellulose to get around R30+ wall. I have already installed radiant barrier 3/4inch foam under the roof trusses to keep the hot air flowing up and out. This has helped a bunch and when up there I can literally feel the heat billowing out of the existing attic into the new space. I intend to put R19 insulation under the foam. I want to keep the attic somewhat conditioned because I am forced to run the HVAC in both sections through it.

So my first reaction was to install a third 3 ton heat pump in that area. However, I read about zoning and my second reaction was to do a zoned 4 ton geothermal unit. Since the geo unit is more efficient my heat loss calcs will be spot on for 4 tons without the efficiency loss of an air source.  However, I looked at several other options.

Geothermal WTW - looks even more efficient and easier to route than central ductwork. Problem is that I have found very little info on water source air handlers for both heating and cooling that are under $2k each. This is insane, it is a fan, with a coil, and water pumps through it. I can get a Rheem air handler for a heat pump, which uses refrigerant, with backup heat strips for around $500. Why the hell is the same thing $2k for water. I also can not find a drop in hyrdo coil for my existing air handlers...

Geothermal WTA. This looks good but requires ducting and zoning between floors. Kind of a pain but doable.

Forced air packaged units - I looked into packaged units when sitting an a local neighborhood and seeing one. Looking at them they seem to use the same amount of electricity while running compared to a same sized geo forced air unit with the exception of no 220 pumping costs. The whole unit comes precharged, sits outside, and a 16seer unit is comprable in cost to a geothermal. The 16seer unit also seems to have a superior low temp efficiency to my existing  air to air units. Without dealing with refrigerant, air handlers, pumping, and the like the extra zoning and ductwork will be acceptable.

Reversed cycle chillers - I have heard people rave about these and their efficiency is compared to a geo unit with the lack of the pipes and need for refrigerant lines. Heated or cooled water is stored in tanks like a WTW unit and moved through radiant heating cooling and with air handlers. Again, insert my hydrocoil issues from the above WTW coupled with the fact that I can find almost no one that sells these units outright. They all want me to pay some dude $7k $8k just to install the outdoor unit and run some pex... no thanks.

Can anyone fill in any of the blanks or know anything that will make the above options simpler? Also, does anyone know of anyone that manufactures a packaged unit that has similar efficencies to the high SEER and COP minisplits that are out? Seems like they would be similar but a little bigger. I like the thought of slapping a once piece unit on the side of my house to do everything. I however dont like the idea if it is going to cost twice what it would to run a geo unit. I want to keep the bills under $200 a month. Seems like with some envelope improvements I am on track for that though.

Lot to go through to there.
Have you considered geo consoles or simply 2 inexpensive mini splits for the 2 rooms. Why, condition the attic?

I have ductwork in the attic. In the grand scheme of things the attic is very small cubic footage. The attic is a hot box in the summer at much hotter than the outside temp. To raise the attic insulation level on the attic floor I would have to rip up all of the plywood the original builders put down. Or, I can install a radiant barrier with 1 inch gap and insulate up to over R30 easily and keep storage. This would prevent the hot air ever entering the structure in the first place negating the need for high R values, keep the convective, conductive, and radiant barriers on the same plane, allow for semi conditioned storage, keep the HVAC ductwork cool, and provide a buffer space for the second floor. Instead of the second floor pooling all of the heat when it rises, the attic would where I dont stay on a daily basis. I think it will work well.

Doing more research on hydro coils, anyone use a hydro coil as a bolt on to an existing air handler or drop in replacement for the existing A coil?

Oh and finally, when my wife goes to work one day and then comes home, the back south facing roof will be white. She will not notice for months or even years since I dont know of the last time my wife ventured into the back yard far enough back to see the south facing roof. However, the utility bill decline might be noticeable.  

I responded to this " I want to keep the attic somewhat conditioned because I am forced to run the HVAC in both sections through it." but apparently you already have duct there. It does make sense to bring the attic inside the conditioned space.

I guess I'm having trouble seperating wheat from chaffe here. That may be why others haven't responded it is difficult to glean if you have a specific question or just want to chat about options you've considered. You've written paragraphs on attic insulation and roof color and one scant sentence about a hydro coil. Coulda missed it.

Hydronic air coils can be added to virtually any air handler. They are quite common in wood boiler applications installed downstream of the homes existing forced air furnace. One has to size it correctly for water temperature as a 50K fan coil at 180F might be 22K at 100F. Many do not come with condensate catch pans and are not suitable for cooling.

Last four paragraphs kind of sum it up. I keep hearing geothermal is so much more efficient but there are four options laid out that are other than tradtional low seer split forced air. The packaged unit I looked at uses the same amount of electricity 1 for 1 with the geo unit. Plus it doesnt have pumping costs. Is there something that I am missing that adds to the savings? Is it the fact that water is easier to transfer heat from and to than air? Or is the geothemal efficiency something of the old 6 and 7 seer heat pump days. That high seer, high hspa packaged system looks awfully tempting. Remember I am also in VA so those 20 deg and lower nights are few and far between. The summer temp also usually tops out at a max of around 105 and that is usually unusual.

Kogashuko,
Are you referring to reverse cycle chillers as well? No doubt air source anything is cheaper to install and under certain conditions can perform as well as geo.

To suggest a reverse cycle chiller is more efficient than a DX ASHP because of the addition of a go between (water) suggests a lack of understanding of how little stated performance (COP, EER, SEER) means.

BTW there is such a thing as water to water geo wouldn't that be most efficient if " .... water is easier to transfer heat from and to than air?"

The only advantage RCC's have over a conventional ASHP is the ability to store a few BTU's. They like to tout the notion that they can be sized bigger without impact on the cooling season which was already true with multi stage and inverter technology in DX ASHP's. In fact you generally do size any air source product larger than geo to get better COP's in cold climates.

Don't be fooled by the fancy name a reverse cycle chiller is simply an air to water ASHP built by folks who don't share the brand equity of the big boys in air source.

Posted By joe.ami on 12 Jun 2013 09:06 AM

...

Don't be fooled by the fancy name a reverse cycle chiller is simply an air to water ASHP built by folks who don't share the brand equity of the big boys in air source.

Amen.

BTW, my 2007 vintage WaterFurnace Water-to-Air heat pumps, Envision series, in first stage, currently run at a measured:

5 ton unit: EER = 20.8 (SEER = 24 - 28), COP = 5.3

3 ton unit: EER = (can't measure due to zoning), COP = 4.8

Measuring system implemented in exact same way as WaterFurnace does (i.e. does not include pumping power), to enable 'apples-to-apples' comparison to advertised specs.

Since I live in the Dallas area, COP is assisted by the warm climate (i.e. EWT doesn't go below 65° F).

(Loop system is designed such that EWT doesn't go above 85° in cooling mode).

Best regards,

Bill

What effect does pump electricity have? I assume very little, but it keeps coming up.

Each pump is a Grundfos 1/6th hp pump, running at 385 Watts.

One pump in the 3 ton circuit.  Two pumps in the 5 ton circuit.

Best regards,

Bill

36,000 / 3414 / 4.8 = ~2200 watts. So I get COP = ~4.1.

I'm sure your COP number is correct for what you're wanting to measure.

Some people want a COP calculation of everything, including pumping and air handler fan power amounts.  And contend that that is the only 'true' measure of COP.

Others want a COP calculation that's reflective of the refrigerant circuit only, excluding pumping power and air handlers.

Major geo manufacturers long decided, right or wrong, they want COP to be reflective of the 'box' they ship, without influence from anything connected to the 'box' that they don't have control over.  So this is what they do for the advertised COP spec.

My clients always ask, "how's it doing as compared to what the manufacturer claims?  Did I get I get the claimed performance I paid for?"  Hence, my implementations of the COP calculation are done with the same calculation methodology as done by the manufacturers. 

I measure COP (and EER) real time using WEL units, analyze the data statistically, and determine overall COP via a histogram.

Best regards,

Bill

Cool discussion. I wouldnt think water to water would make much of a difference as those who make the reverse cycle chiller claim but it would somewhat make sense. IF you were taking a set amount of water and making it a set temperature and your only heat loss gain of the water was in the structure it would take a lot of error out of things like sizing ductwork, and refrigerant charge (like geo or packaged units you wouldnt be pumping r410 50 feet like in my upstairs unit.) Thus making it more efficient or efficient as it could be. Also, the air to water as I have mentioned. No matter how any of the systems work it is simple physics that it is easier to transfer heat in and out of water than air because it has a much lower specific heat. The issue is then that you still have to transfer the heat in or out of air somewhere else. But if your system was oversized and heat loss gain in the holding thank was inside the encapsulated area you in theory would never suffer from the effect the colder outdoor air has on the DX system indoor forced air temp. Again same would be true with geo. I was also told that the water to water systems should be the most efficient but that is only measuring the pump unit not the efficiency of transferring that heat to and from the air somewhere else.

The reason I threw out electricity is because of all of the COP, EER, SEER, and other units used in calculating efficiency and some in different modes. All are usually based on a set outside temp or water temp. However, if my packaged unit takes X amount of Watts to run and I am comparing it to a geothermal unit that takes X amound of Watts to run and they make the temp of my house the same, how would a Geo unit possibly save me money if there is still extra pumping costs? The only factor that could possibly be different, unless I am missing something, would be run time? When looking at the published power requirements for both units they are very close. I could see, again in theory, that a reversed cycle chiller with fixed outdoor coil size and packed unit both fixed coil sizes could take any margin of error out of ground loop design efficiencies. Is this enought to bridge the difference between geo and air source? Can I really trust the COP numbers?

So when it all comes down to it will I actually see a difference on my utility bill. Will the savings actually outweigh doing something like replacing my electric water heater with a heatpump water heater? I will be doing either install myself so the extra excavation costs will be minimal and require only my time. Of course loop design will require a lot of thought and double checking my numbers since it will be the first time I do this.

Do not forget that you have water subjected to outdoor temps with the RCC, so in areas subject to freezing temps, antifreeze will be required which will likely lower COP a significant percent.

These products may have their place, but if I were going to go air source I'd like to go with one of the bigger (reliable) names.

BTW you may not like the price of a Hydronic vs a DX air handler. Hydronic systems climb in price very rapidly.

Why in god's name is the hydronic handler so expensive. It is the same as a DX but you run water through it instead of r410a. There should be no difference minus the coil design and fan speeds. Hell, you could probably pump chilled or heated water through a regular A coil and have it work.

I agree with you Bill about COP values, thanks for the info. I'm interested in comparing to an air source heat pump. Not sure if they include the inside head fan usage. But looks like WtA geo, even with a very high performance loop (65F to 85F), might be COP = ~3.5 when pumps and fan are included.

> When looking at the published power requirements for both units they are very close.

You don't want to use those maximum figures for anything other than circuit sizing.

"Why in god's name is the hydronic handler so expensive. It is the same as a DX but you run water through it instead of r410a. There should be no difference minus the coil design and fan speeds. Hell, you could probably pump chilled or heated water through a regular A coil and have it work."

Volume of sales and market. It's even worse if you want a hydronic console as I recently ordered its 2-3 as much as a vertical airhandler.

Rheem was very nice when I contacted them a couple years ago before putting in my units and provided the actual load that their 1.5 ton and 2 ton condenser units used. For the life of me I can not find the email. However, if I remember correctly it was a lot higher than similarly sized geo and packaged units.

I would love to see some real head to head testing data.

I guess runtime is also a factor because during those 20 deg days my air source units run almost non-stop to get heat out of the air. In the case of a water source the loop should still be much warmer than the air and run time would be less. As for the summer, mine do not seem to be effected much by the very high heat. I think I might have had one day last year that actually got hot enough to cause the second floor thermostat to have trouble below 74deg. That was before the ridge vent and without the attic conditioned.

Manufacturer extended performance tables, generally available online with a bit of sleuthing, contain power input for a wide range of water and air temperature conditions. That your Rheems are not "effected much" by very high heat is likely an artifact of their being a bit oversized. What you likely did NOT perceive is that their operating power rises substantially with increased outdoor air temperature.

I'm not sure I buy the argument that water is easier to heat / cool than air. Unless you are a fish LIVING in water, water serves only as a transfer medium...ultimately the air needs to be heated or cooled by being blown across a coil, whether that coil contains water or refrigerant. I'm leaving radiant out of this conversation since it does not appear to be on the table, and it is generally unsuitable for cooling anyway.

Posted By jonr on 13 Jun 2013 03:16 PM
I agree with you Bill about COP values, thanks for the info. I'm interested in comparing to an air source heat pump. Not sure if they include the inside head fan usage. But looks like WtA geo, even with a very high performance loop (65F to 85F), might be COP = ~3.5 when pumps and fan are included.

Under the old ARI standard, this energy input for circulation pumps was not included in the calculation of the total energy input, and the standard specifies the water flow rate that results in a 5.6 °C (10.0 °F) temperature change across the heat exchanger. Under the new ISO standard, the test must be performed at the mass flow rate specified by the manufacturer, and the energy input to the water pump is calculated and included in the total energy input. A pump power correction has been added onto the existing power consumption. A standard formula is used to account for the pumping power, to ensure customers can make direct comparisons between different models. Within each model, only one water flow rate is specified for each performance category, and pumping watts are calculated utilizing the pump power correction formula: (gpm x 0.0631) x press drop x 2990) / 300. ISO Capacity and Efficiency Calculations The following equations illustrate cooling calculations: • ISO Cooling Capacity = Cooling Capacity (Btuh) + (Blower Power Correction (Watts) x 3.412) • ISO EER Efficiency (W/W) = ISO Cooling Capacity (Btuh) x 3.412 / [Power Input (Watts) - Blower Power Correction (Watts) + Pump Power Correction (Watt)] The following equations illustrate heating calculations: • ISO Heating Capacity = Heating Capacity (Btuh) - (Blower Power Correction (Watts) x 3.412) • ISO COP Efficiency (W/W) = ISO Heating Capacity (Btuh) x 3.412 / [Power Input (Watts) - Blower Power Correction (Watts) + Pump Power Correction (Watt)] So you see that water circulation is actually accounted for in the ISO standard 13256-1 rating. It is always enough power to push enough water through the entire loopfield. That depends on the loopfield design and the equipment you choose. The manufacturers are actually quite upfront about the different ratings systems and details he differences in their spec sheets. Some examples are as follows: http://www.johnsoncontrols.com/content/dam/WWW/jci/be/integrated_hvac_systems/hvac_equipment/indoor_packaged_equipment/water-source-heat-pumps/146.00-EG2_(310).pdf page 15+16 http://www.climatemaster.com/downloads/LC363.pdf page 12 www.waterfurnace.com/literature/envision/sc1000an.pdf page 8