I'm trying to decide between a Waterfurnace series 5 and 7. In general, I'm most interested in having a very efficient system long term and would definitely prefer an increase in efficiency over upfront cost (but I don't want to pay more for negligible gain, of course).

My house has on the order of 20 vents. It is currently heated/cooled by a 3.5 ton outdoor unit (heat-pump/ac) with a 5 ton blower indoors. We are planning to install a 4 ton waterfurnace unit with the static blower motor (or possibly the 5 ton system motor). (My installer has also suggested going with the 5 ton Waterfurnace unit although all others suggested the 4 ton.)

My installer believes that a Series 7 would not be a good fit for us. He said it will slow way down (achieving good efficiency for the air it reaches), but when this happens, distant vents, like those on the top floor won't get much air. He is basing this off a comment I made that the upstairs is significantly warmer than the downstairs in the summer (which is true).

I asked if the system would be able to speed up the fan but continue to run the compressor at a slow speed. He said that would not work great and the ac would not pull the humidity out of the air as well as it should. (I'm not sure if it's possible.)

Does everyone agree that a series 5 seems best in this case? Does anyone know of a good setup for my situation where a Series 7 would give me some gains?

Thanks.

If you upstairs is significantly warmer, put a zoning system in, preferably the intellizone 2 from Waterfurnace. It is the only zoning system which can, in combination the the 7 series, reduce the blower and compressor speed for smaller zones.

Yes, for more humidity control you need a colder coil -> more condensate. Again, the 7 series has this active dehumidification control where you can slow down the blower to control the humidity better, and increase the compressor stage, something no other forced air geo system can do.


Usually upstairs is warmer than downstairs in the summer due to higher heat gain. I probably sound a bit bias here, and maybe I am, but the units are really that good, it is hard not to enthusiastic about the technology. Make sure that your installer is not bias against it, since you need to take some training from Waterfurnace and be certified to be able to sell the 7 series.

Thanks for the input again.

He mentioned that it would be good with zoning too. Unfortunately, zoning isn't really an option for me. I'd have to completely redo all the duct work of the house.

The concern is that when the blower slows down the air won't get upstairs. (Those ducts are furthest from the unit, not surprisingly.) I know upstairs being warmer is pretty normal, but I'd like to minimize that as much as possible. Sounds like it may be an issue with the 7...

I've always been under the impression that slower velocities would improve (relative) flow to distant zones, whether that be in an air or water flow models. Pressure losses are typically a relation to the square of velocity, so as velocities decrease, pressure drop would decrease exponentially. So at lower speeds while flow to all zones would decrease, the ratio of flow between higher and lower resistance zones would benefit those with more resistance (further out). (CAVEAT....These are the musings of a theoretical and non-practical engineer with the assistance of gin)
witness pressure drops and exponential increases. http://www.pacificpumpandpower.com/docs/Friction_Loss_Table.pdf

Hmmm, very interesting thought! Thanks! I'll look into this. Anyone else know anything about this. Specifically, does anyone know if there are theoretic assumptions here that are not realistic for real ducts and throw this argument way off?

What is the worst case if I went with a Series 7? If I had problems, would I be able to set it's minimum speed to X so that it didn't slow down too much? Is this something I could do personally as a computer-savy and semi-engineer homeowner, but not someone who has expensive special diagnostic tools or access to non-public information or manuals? If such a setting exists, is it pretty fine grained (i.e., can I select from 100 different minimum speeds or do I only get to pick from 3)?

Posted By mtrentw on 20 Mar 2014 07:42 PM
I've always been under the impression that slower velocities would improve (relative) flow to distant zones, whether that be in an air or water flow models. Pressure losses are typically a relation to the square of velocity, so as velocities decrease, pressure drop would decrease exponentially. So at lower speeds while flow to all zones would decrease, the ratio of flow between higher and lower resistance zones would benefit those with more resistance (further out). (CAVEAT....These are the musings of a theoretical and non-practical engineer with the assistance of gin)
witness pressure drops and exponential increases. http://www.pacificpumpandpower.com/docs/Friction_Loss_Table.pdf

Pressure drop increases with higher flow. Thus it should be lesser impact with the 7 series at lower speed. You are correct.
You can ask your installer to also order you a service tool if you want the control and know what you are doing, so you can dial in the blower settings. The instructions are in the installation manual. I believe you have 6 different minimum blower settings out of 12 blower speeds, but check the manual.

marmot.
You don't have to redo all duct work to zone (Google the Arzel system).
Your installer doesn't seem to know a lot and recommends a size larger than everyone else, why is he a good pick?

Thanks. I'll have to look at the Arzel system tomorrow.

I chose my contractor primarily because he was the most highly recommended (by numerous people at work). I got three estimates. One was about the same as this guy, and one was about $5K more. (I'm looking at paying about $29K before tax incentives.) Recommendations are the most important thing for me though, but the price can't be too far off the mark.

My experience with contractors is not great, and I'm not convinced any others would be better (although I could be wrong).

I appreciate all the help.

This is super useful! Thanks (mtrentw and docjenser).

When you say service tool, you mean the AID, yes?

Posted By marmot on 25 Mar 2014 10:20 PM
This is super useful! Thanks (mtrentw and docjenser).

When you say service tool, you mean the AID, yes?

Yes, Aid Tool. Keep in mind that the 7 series has its own proprietary zoning controller. Intellizone 2. Check it out, it controls the variable speed nicely.

I'm looking at this friction-loss paper again, and I'm not convinced it applies. It's referring to friction loss, so assuming I had perfectly sealed ducts with no vents on the way to my upstairs, I definitely see how it applies.

However, I think one of the most significant factors in my case is pressure loss due to holes in the pipe/ducts, namely leaks and vents. Even if my ducts were sealed perfectly, there are vents on the paths to reach the upstairs. I don't have any scientific characterization, but I wouldn't be surprised if a greater _portion_ of the pressure drops in those first holes when the velocity/flow is low.

Does anyone know?

I've been trying to look up the Arzel system, but it's not really clear how it works. Is there a good explanation on all the different dampers? Unless I want to start tearing out lots of drywall, I would essentially need many dampers that I could install from the vents themselves to block each corresponding vent but allow air to keep moving through duct behind it. I'm having trouble envisioning how this could be possible.

I have an oval pipe installation where things quickly spider out from the heat-pump and run to the different sides of the house.

Could this really be feasible and a good idea?

As I'm thinking about this more, I'm wondering if some of my previous comments were misguided. Is it normal for a duct to end at a vent, or is it also common to see vents in ducts that continue to other parts of the house? (I.e., my comments/concerns about ducts continuing past vents may have been wrong.) One source of my confusion (if I was wrong) is that I currently have at least 4 vents directly attached to my mains in my basement. Is this a somewhat horrible thing? It's something that could be fixed.

Otherwise it may be that each of my vents has a dedicated oval duct? Would you expect that to be the case?

If this is the case, and I fix the vents on my mains, then it would make sense to me that friction loss would be the main concern. I'm curious to hear other thoughts though.

A picture is worth a thousand words........
Generally the main trunk would have 1 tap for each opening on the other end. These would start as 6" round (again generally). Code minimum duct would generally employ 6" round to downstairs openings and 6" oval to upstairs. 6" oval has the friction loss of 5" round so therefore you have the shortest runs served by the best pipe and the longest supplied by the worst. it is easy and inexpensive to avoid in new construction, but usually not by the lowest bidder.

RE zones if you catch each pipe as it leaves the main trunk you can close them individually.

Something seems amuck here, i would be surprised if a 3 ton waterFurnace 7 series would not work for you.
Where are you located?
I show with loop temps in the 30 degree range, you are getting 36K BTU's of heating capacity out of the 3 ton 7 series, and if you have 40 degree water you are getting 42K BTU's of out of the system.
If you had a 3.5 ton heat pump that equates to around 40-42K BTU's and on colder days(17F or so), probably closer to 22K BTU's, so a 4 ton might be oversized for you. If sizing based on cooling capacity you need 70 degree water temps to get 3.5 tons of cooling out of the system, but it does have superboost mode which will increase capacity up to 130% of rated or so, which means you really can get around 50K BTU's of cooling out of a 3 ton system with 70 degree water or 3.5 tons with 90 degree water.
I would have some major concerns about the company wanting to go from a 3.5 ton air source to a 5 ton geothermal. Thats like saying, well your half ton pickup hauled that 5,000 pound trailer just fine, but with your new truck we better be safe and get a 1 ton diesel with a 30K pound towing capacity to make sure your new truck hauls your 5,000 pound trailer.Which truck will save you the most money on fuel long term, which truck costs you less up front, your geothermal system is very similar the 3 ton or 4 ton will cost you less down the road and will cost you less upfront.

For the airflow issues the 7 series has speeds 1-10 for airflow plus 11 and 12 for superboost/auxillary heat settings. This is NOT something you can change but should be included in your install would be setting up and dialing in the airflow. If need be they can set compressor stages 1-2 for fan speed 1 or for fan speed 5, thats a range of 285 CFMS up to 815 CFMS for compressor stage 1-2


My company has installed lots of the WaterFurnace 7 series, probably 1 per month since they came out in August of 2012. We have videos of them operating on my YouTube channel which is in my signature.

Sorry for the infinitely late reply, but thanks a lot for your thoughts and all the details.

I'm in the Baltimore area, FYI.

I had no idea that a 3-ton geothermal heat pump could actually have a different capacity than a 3-ton air-source heat pump. (However, if I understand your post correctly that actually is the case sometimes.) I thought the "tonage" was equivalent to the capacity. ("capacity" may not be the right word, but I mean ability to heat/cool a certain amount of house.)

Unfortunately, at this point there isn't much I can change. I'm getting a 4-ton waterfurnace series 7. In retrospect, I may have gone with a different installer, but this one was the most highly recommended by people at my work. (Recommended by two people, and there were one or two negative recommendations for other installers although there are a lot in the area.) (He seems very focused on making sure his customers are pleased, but I'm getting the impression from information like this and other sources that he may not always make the right decisions.) He was not the cheapest.

A 3 ton heat pump (air or ground source) has 3 tons of capacity depending on entering air or water temperature. Because we can impact entering water temperature with design choices, we can get more out of aground source heat pump when it is cold out (and air source heat pump capacity is down due to low ambient air temps).

Airflow will go the path of least resistance. So as the velocity decreases and the associated resistance decreases, airflow will most likely go towards the closest vent and the furthest vents will be out of luck. At higher velocities, the resistance increases at each vent, and thus, the airflow will want to go further down the trunk which will split the airflow more evenly. For the best results a 10:1 pressure loss at each dropleg vs the trunk will result in good flow splitting. Good ole' hydraulics at its best.