A Waterfurnace GeoPro dealer proposed a 7 series NVV036 for a tri-level residence with a heating load of 51,300 and a cooling load of 31,500 for about $32,500 with the optional variable speed flow center, 2 wells @ 280' each, and 0.40 grouting. As an alternative, he proposed a 5 series NDV049 for $3500 less. Since he was offering a 10% discount w/o the financing option, that'll pay for the 7 series, which is preferred. I was told that the NVV036 is a 3-ton cooling/4-ton heating unit. Based on advice from gmith (iirc), I ran the numbers on Loop Link, which I never used before, and found that the NVV036 would provide an installed COPavg of 4.28 and EERavg of 25.5; or the NVV049, I got a COPavg of 4.95 and EERavg of 24.5. That's a big jump in COP for an added $3200 (for the 7-series NVV049 and 635' of boreholes); however, the dealer's data from GeoLink (4.23/26.1 for 7-series NVV036 and 4.26/31.4 for 7-series NVV049) showed no appreciable change. The elephant in the room is that the actual ceiling R-value is highly variable, so the heat loss/gain could be off substantially. I need to seal the deal ASAP. My questions: (1) can the 7-series NVV036 provide 4-tons of heating? (2) Will there be a big COP difference or not between the 7-series NVV036 and NVV049? (3) Should I go with the dealer's recommended 7-series NVV036 and 560' of boreholes or the 7-series NVV049 with 635' feet of boreholes?
I don't understand why you are focused on COP or EER. Those parameters are an outcome of the unit operating under a particular scenario. They are dynamic and different at any and all operating points. You should be focused on the ability of the particular unit to heat or cool the house, ie can it provide 51,300 BTU/hr in heating or 31,500 BTU/hr in cooling. Anything less and you will be freezing/sweating and out lots of money. The nameplate capacity (ie 036 implying a 3T unit or 049 implying a 4T unit) provides an approximate capacity only just to differentiate between units. But, the true unit capacity varies with incoming water temperature. Assuming this is a closed loop system, I would rate each unit for heating at an incoming water temperature of 30F and each unit for cooling at an incoming water temperature of 90F. The ground loop temperature of a closed loop system varies seasonally and doesn't stay constant. Take a look at any system on "welserver" (Google it) to see this in action/understand this concept. Using those values (30F/90F) will make sure that in the dead of winter (incoming water temp at 30F) and peak of summer (incoming water temp of 90F) you have a reasonable approximation of the heating capacity and cooling capacity, respectively. Per Waterfurnace's specifications, a 5 series NDV049 has a maximum heating capacity of 38,400 BTU/hr at 30F incoming water and a maximum cooling capacity of 50,100 BTU/hr at 90F incoming water. The 7 series NVV036 has a maximum heating capacity of 37,400 BTU/hr at 30F incoming water and a maximum cooling capacity of 35,200 BTU/hr at 90F incoming water. Those are the raw values in the specifications manual for each and haven't been adjusted for incoming air temp, antifreeze added to ground loop, etc. So the actual numbers will be a little less and suffice to say, neither will cover your heating load although both will cover your cooling load (the 5 series less optimally because it is so oversized for cooling). So that means you will need electric strip heat to supplement the units in the winter likely for a good strech of time. So ignore COP and EER because you will have an electric strip heating unit (COP of 1) for probably a month (or more) during the winter if you use these units being suggested. If you wanted a geo unit to cover your full heating load, you would need a 5 series NDV072 or a 7 series NVV060. Its close to working with a 5 series NDV064 or 7 series NVV048 ( both good for 47600 BTU/hr) with some small amount of electric strip heat use (likely a few days a year on coldest week) and that might be the cheapest option to balance correct unit size/upfront cost. But, i would point out that with three floors, there is a good chance that very good zoning is going to be needed to control temps at the top floor vs the lowest floor with 1 unit. Your overall heating load and the zoning issuing is screaming use a two unit system to both better cover the load profile and even out temps. This would likely double your current cost but actually provide a workable solution. 2 wells at 280' or 2 wells at 318' (you also mention 2 wells at 367.5'?) - these values are assinine - premade loop pipe comes in big graduations like 350ft or 400ft for 350ft or 400ft wells. Regardless, these well lengths are not a lot of distance and it makes no sense why you would have different well lengths for different units. More importantly, I have 2x that amount of well length for a smaller load profile. Mine works very well but I did hit 30F incoming loop temp in the dead of winter so I know its appropriately sized. How good are these inputs to looplink? Like any other computer modeling software, its garbage in garbage out. you have to know how to input correct data to trust the output Keep in mind, the unit capacity handles instantaneous extremes in heating/cooling. The well capacity (its length) needs to be able to handle the yearly seasonal heating/cooling in total - the instantaneous heating/cooling are blips on a yearly scale. So typically, the well length isn't dependent on the unit capacity specifically if the units are being properly sized. No way should you ever use 0.4 grouting for the wells - that is like straight bentonite grout and is terrible for heat transfer. Your grout coefficient should at least match the ground/rock's heat transfer coefficient or otherwise the grout is an insulator and not a conductor relative to the ground. Its very easy to get grout coefficients of 1 - they should use something like GeoPro's TG Lite+Power Tec grout mix. Its silica additives (PowerTec) that get mixed in with the bentonite grout (TG Lite). Geo Pro will even test it for free too to confirm installed grout if you send them a sample. For what its worth, I modeled my wells in LoopLink using a grout coefficient of 0.8 and got tested results from GeoPro of anywhere between 1 and 1.6. In summary, I would go with neither of the dealer's recommendations and take a hard look at what you actually need to properly heat and cool the house. Its not clear to me that either you or the dealer understand what is needed. If you are shopping based on cost (and the dealer is happy to provide a system based on lowest cost not actual need), that is a recipe for disaster.
Wow! You always provide such great feedback. What I thought was appropriate was the 7-series NVV048 with 4 boreholes @ 150' each and 1.00 grout (0r 4 boreholes @ 180' depth each w/0.40 grout). The WF GeoPro dealer, whose driller uses 0.4 grout, told me: "...the 7 Series is a 3 ton nominal cooling 4 ton heating system. It's intentionally de-rated by a ton for longer run times and higher comfort and dehumidification. The 7 Series does have an option that unlocks the superboost feature and allows for the full 4 tons of cooling for up to 24 hours at a time. I'll be honest, the 720 ft of bore is going to be a waste of your money. I can look into the high conductivity grout if you insist. Honestly this kind of doubt about every aspect I propose is why I originally turned down this project." He also told me, when presented with the extensively-detailed engineer's heat loss/gain report: "I'm happy for the engineer to run some numbers, but they're not realistic at all. Those sheets are nice for him to show you and charge a bundle, I'm sure, but that's not what I'll feel comfortable using. I'm sorry, it's nice eye candy but I'm afraid not much else." I've been told by the WF GeoPro dealer to just trust him, the system will work fine. Cost is the least of my concerns, I want a system that will operate efficiently, not just work. P.S. I mentioned only 2 wells @ 280' for the NVV036 or wells totalling 635' for the NVV048.
NVV048 is at least a respectable choice recognizing that from a modeling/estimating standpoint the use of electric strip heat will occur at some point (4T unit covers like 93% of the heating load). Some winters never, other winters for a week, most probably a day or two. Its not the end of the world and balances upfront cost and efficiency. I don't know what the premium is for a 5T over a 4T 7 series but over 25 years with elec heat coming on a few days per year, it may not be worth upsizing to the 5T unit to eliminate the elec heat aspect. For drilling, I was told by my driller (they are a huge outfit only doing geo drilling, loop install, and grouting out of MD) that it is more efficient to to make the bore depths deeper (up to about 500ft) than to have more bores because it takes time to setup and move the rig. Below 500ft and you need bigger equipment and start to get into state issues with a "mining operation". I don't how much of that is all true, but assuming it is accurate, I would probably do 2 holes at 300ft each unless there is some geologic formation preventing that. His description of the 7 series function makes no sense. There is no derating. Its a multi-stage unit. If it needs to be on stage 5 to handle the thermostat's call for heat, it will. If it needs to be on stage 12 to handle the thermostat's call for cooling it will. But a 3T unit won't put out 5T of heat. I don't get the contractor's position. You are asking him to install more well length, higher conductivity grout, and a bigger unit and he doesn't want to with both of you knowing that you will pay him more money to do that versus the system he is proposing? Why would he care if you want a better system and are willing to pay for it? Being an engineer myself, I can get that sometimes contractors aren't thrilled being told what to do (which is crazy because most contractors don't want to "design"), but if he doesn't have any reasoning behind why his cheaper system will function just as well, I would run away. With you providing an engineered design, he is essentially off the hook if it doesn't perform (assuming he builds it as designed). What is his downside? My installer was a GeoPro dealer too and even had a WF rep come out to evaluate the loop pumping (system was bigger than anything the dealer had installed prior). I can tell you the dealer had no idea regarding sizing, function, or even what parts work with other parts. Initially I was trusting but when a few things went of the rails early on, I took a much more proactive approach. My system is better for it and frankly the dealer seemed to be happy with my involvement because it felt like they were over their head at several points. I absolutely wouldn't want a contractor that wasn't interested in your opinion when you are the one paying for everything (his errors too). WaterFurnace was useless as well. Installer would query them with questions on the install at several points and I got the sense from the tech installing stuff their response was mostly a shoulder shrug and not sure what to do. I am convinced that at a residential level, no one individual seems to understand the "system" and each focuses on their own little part dooming the system. But the "system" is what gets you efficient heating and cooling. If one part doesn't work, the whole system doesn't work. You need correctly sized units to get heat and cool. You need adequate length of well to get that heat to/from the ground, and you need appropriately sized ground loop piping and loop pump so you don't take all the potential efficiency of these systems and throw it out the window with water pumping. Anyone can get water to move around piping by throwing energy at it, doing it efficiently is the key.
I'm an engineer too, so here's another long answer. Seems like many HVAC guys don't like dealing with engineers, because we want to understand what we're getting, ask a lot of questions, sometimes understand more than they do, and sometimes think we know better than they do when we do not. To answer your questions: 1) No. The AHRI ratings of the NVV036 are 32,000/13,000 BTUH for Full/Partial heating. So, the NVV036 will not provide 4T of heating. Looking at the submittal data for the NVV036, it will output 4T at incoming water temp or 70 degrees, but you won't see that. As gsmith22 pointed out, the incoming water will be colder. 2) There shouldn't be a big difference in efficiency between a 3T and 4T 7 Series. A larger unit running on lower stages has a higher COP, so the 4T might be more efficient. Also, the 3T might need AUX heat more often, which will lower overall system efficiency. 3) Based on the loads, you could probably use either one, with the 3T using more AUX heat. I also don't think you should focus too much on the single COP and EER numbers reported by the software. To decide between the 4T and 3T I would look at operating costs, performance vs outdoor temperature, and sizing vs the house load. Things to consider in the decision: 1. How does the output of the system compare to the heating and cooling loads of your house versus outdoor air temperature. The modeling software tells you this. 2. What is the operating cost difference? The modeling software tells you this. I would use the numbers to compare units, not as an absolute prediction of costs. 3. What is the thermal balance point--the outdoor temperature at which AUX heat will be required? What's the projected cost of AUX heat? 4. What is the impact of ~50% more loop piping on the required flow center and the associated operating cost. Can a single pump handle it? Free online software from Geo-Flo can tell you this. Your dealer doesn't sound very cooperative, but I would ask your dealer (maybe a different one) to run the GeoLink report for the systems you're comparing. Ask him to use your actual electric rates. Then look at the operating cost differences. Also look at the balance point temperature and the Bin data for operation vs outside temperature, to see how well the heat pump keeps up with the load. If you don't want to ask the dealer, you could also do most of this in LoopLink yourself. Look at the Zone Summary page on LoopLink. What does it say for the sizing percentage? Look at the graph. At what temp does it cease to meet the load? You also need to have pressure drop calculations for the loop piping to optimize the pumping setup and you need to understand what flow center will be installed. I had my dealer use larger pipe for the supply/return run, which vastly reduced my pumping power and allowed me to use one VS pump. I have a 7 Series NVV048 in a 3-level house with loads of 53,998 heating and 39,419 cooling. GeoLink says it will handle 100% of the heating load. LoopLink says the NVV048 will cover 98.9% of the heating, and is 9% 0versized for cooling. The 4T would be more oversized for cooling in your home, but variable speed technology makes oversizing less of an issue. I have Intellizone2 with two zones. My setup was limited to two zones by existing duct configuration. It works pretty well, but there are some things about the staging in heat mode that I'd like it to do differently. I haven't used the system in Summer yet.
Per the attached engineer report, the heating demand is 51,600 Btu/hour and the cooling demand is 31,500 Btu/hour. for an interior of 3800 sq. ft. (Basement= 38%; 1st Floor= 38%; Loft= 24%). The attached GeoLink report from the GeoPro dealer uses 60,000 for heating and 48,000 for cooling, the alleged system output for the NVV048, not what the residence would require. The "IMG" attachments are 4 of the 15 pages of output from Loop Link that I did (keep in mind I am no expert); I was attempting to use 2 holes @ 280' w/0.40 grout, as proposed by the dealer. Thanks to the feedback of gsmith22 and SShaw, the NVV048 gives me a warm fuzzy feeling. The climate in Southcentral PA (Harrisburg) is slightly cooler than MD. Electric is chap here (6.6 cents per kWh). How do I nail down an appropriate total borehole depth and grout conductivity -- that's my main concern at this point. No one wanted to deal with retrofitting the ductwork for zoning and I get reasonable blending by having the HVAC a on CIRC. Not an optimal solution, but one that I am told can be dealt with (for an added cost) if the tri-level comfort is less than acceptable.
i quickly glanced and it looks like the heating and cooling values are reversed from the engineer's load calc - ie your cooling load is 51,300 and your heating load is 31,500. but then the other documents show it the other way around. that would substantially change the discussion. I would get that clarified first
Unfortunately, that GeoLink report is pretty useless as is. It should have been run with the actual heating and cooling loads of your house. The report also needs to be run with the correct delta-temps corresponding to your local design temps and your indoor set points. The delta-ts need to correspond to what was used in the load calculations too. My GeoPro dealer got the delta-ts wrong the first time he ran GeoLink for me, and I had to ask him to do it again and tell him what needed to be changed. If your dealer knew how to read the report he would see on page 4 that the NVV036 fails to meet the (incorrect) cooling load above 82 degrees, which isn't good. As gsmith22 noted, the heating and cooling values are reversed. Also, there is no value for latent cooling, which there should be. I can't say whether those loads are right, but you might want a second opinion. I did my own calculations using hvac-calc software. There's a user on hvac-talk dot com (dan sw fl) who will do a ballpark load calc for you. I don't care much for that site's rule though, and there's nobody I've seen on there who's an expert with geo, so I wouldn't bother asking about that. gsmith22 will need to help on the bore holes. My system uses two horizontal trenches.
My understanding of the engineer's report is that the nomenclature is misleading. The heating Btu is the solar energy gain, the BTUs of solar energy that are heating the residence, so this would be the amount of cooling that the HVAC system would need to provide. Similarly, the maximum cooling is the amount of heat being sucked out of the residence by the environment. The engineer's focus is on heat gain/loss by the structure. I will confirm this, but I do live in a heating dominant climate. I did do a cursory check with the demo version of Wrightsoft's Right-Suite Universal (ACCA Manual J, 8th ed.) and the numbers were similar to those of the engineer. On SShaw's point about the NVV036 not being able to cooling load above an OAT of 82F, can you explain to me, who certainly does not understand, what column shows this and why? Is it because the System Geo Air value is less than the Space Load column?
that would be a weird usage of nomenclature and I'm not sure if that is correct because you won't have a sensible and latent heating load - that is specifically for cooling and de-humidification. Plus there are a bunch of dates associated with this max load that are all in the summer/early fall. CoolCalc (google it) to use if you want to check the building loads that your engineer came up with but I'm not sure they are wrong just confusion over how to use the output. CoolCalc is free to use - you only have to pay if you want to print out the results ($15 for 5 prints) but it can be used to confirm the building loads if there is some suspicion of a problem. Remember, these are the instantaneous max heating and cooling loads your house will see. So its entirely possible that you peak cooling load can be higher than your peak heating load depending on the amount of windows and which direction they face - this is especially true for lots of glass facing west which will create a huge instantaneous cooling load - your "great hall" seems to have that issue. Total heating for the winter can still be more than total cooling for the summer in this paradigm but instantaneous values can be reversed. If I remember correctly, load calcs for Residential (done in accordance with ACCA/Manual J) do not to take into account heating from sun through windows during the winter so the actual heating load may be less. Have to get the loads straightened out before moving forward. everything else flows from that
Regarding your GeoLink question... Look at the Loads column. This shows the heating and cooling load on the house as a function of temperature. Load is proportional to temperature difference, inside vs outside. Then look at the Geo Air Btuh/hr column. This shows the heat output (or removal) of the installed heat pump. Variable speed will adapt to match the load. Above 82 outside the Nvv036 heat removal falls below the load. Below 22 the heat pump falls below the load and AUX is required.
I thank both of you gentlemen for enlightening me. @gsmith22 : the Great Hall at the House of Anjou is a 17' high wall of glass facing magnetic South, with additional glass facing West, not to mention a fantastic view -- what great insight you have provided. Time for me to chat with the engineer for the correct interpretation of his results and to inquire about the missing latent cooling!
