I appreciate any advice that any of you might be willing to give. Here is my situation. We moved into our house in Southern Illinois in 2006. At the time we had installed a "Water Furnace" 6 ton Geo unit that had "Geo-Comfort" name on it with 150' vertical loops for a 3 level house. Basement has about 1600 Sq ft, main level 2200 Sq ft, upper level around 1100 Sq. ft. The house has 4 temperature zones: (Basement, main level, upstairs, and bonus room). A few days ago our Geo unit went down. This is the second time within 3 years that a compressor has gone bad. I also had to replace a drain pan that cracked several months ago. A technician said that my ECM is bad and that a coil is leaking. He also said that the ductwork in the mechanical was poorly installed. He used the term "Cap and Tap." He stated that if they would have installed it the by-pass would be farther away from the unit, plus they would have not made an elbow to turn the airflow but rather "curving" the airflow to make more aerodynamic. He also stated the compressor could be going bad because if one of the small zones calls for the unit to kick on that the ductwork might be too small to handle all the air from the 6 ton unit. By the way, we have cellulose insulation.

Honestly, I have never felt at ease that I am getting the efficiency out of this unit.

Here are the solutions that have been proposed:

1) Replace the parts and repair the current unit (prob about $6k) - No warranty on current unit (I don't like this option)

2) Replace the unit with a new GeoComfort 6 ton unit and do some modifications to current ductwork by making it more aerodynamic and moving by-pass away from unit (prob $15K). New unit will have 10 parts and labor warranty. He said this would also cause improvement to my current situation and the improved modifcations to the ductwork could also help with efficiency along with the newer unit. The only ductwork modifications can be made in mechanical room. 3 level house has finished basement and ceilings. I don't want to have to tear out drywall.

3) Tech said this....If you want to do it the best you can, you probably need a 5 ton unit in the basement to heat and cool the basement and main floor. Then we can put a 3 ton unit in the upstairs that can control the upstairs and bonus room. You would also have to have probably 1-2 more holes drilled which would cost about $1500 a hole. This would lighten the load on how hard the units would have to work, ensure good quality airflow and "MAY" cut your electric bill. Cost to do this is around $35K. He said it might cut bill by $100 which would take about 30 years to recoop the costs in savings.


My thoughts:  This is a different company that is doing the repair work. They are highly reputable and have excellent customer service. They are known in the area for being pricy but they are good. If the current unit would have not went bad I would not be having this discussion. We, for the most part, have felt the house is cooled and heated properly.

Any input that you might have would be appreciated. If you need any pictures or for me to be more specific, I will do my best.

Hope to hear from some of you soon.

Thanks.

DJ

6 tons sounds like too much for the home and definately a problem with 4 zones. 8 tons is crazier.
If tech is talking about a bypass damper is it electronic? the barometric or weighted ones don't work with ECM blowers.
Start by getting estimates and shopping as though you are going brand new. Look for contractors that run manual J calcs.
You need very sophisticated zone equipment and a bleed strategy to subdivide so much. If there is room in the mechanical room you might go with 2, 2 ton units or so.

Bypass damper is electronic. I'm curious about your thoughts that 6 ton is too much. Here's the problem I am running into is that no 2 people will say the same thing. So you think a 5 ton unit would be sufficient? I'm still going to inquire about this with other HVAC personnel.

What you need is a proper "Manual J" It should be done room-by-room, which will reveal how much air each room needs. I use Elitesoft, which allows me to assign rooms to zones (presumably Wrightsoft and others allow the same)

With room and zone airflows in hand look at the minimum airflow the system requires. With a six tonner, that's probably around 1400 CFM. Chances are that's at least double your smallest zone's needs. Strategies for coping with overblown zones and system minimum airflows include oversizing ductwork within small zones and "cracking" a large zone's damper (never allowing it to fully close)

Notice I didn't include bypass dampers as a viable small zone strategy. I'll likely take some flak here, but I refuse to install bypass dampers, and I routinely deploy 3 and 4 zone systems. Bypass dampers introduce several problems - they reduce efficiency and even threaten compressor health in heating mode since they dramatically raise return air temperature and thus refrigerant discharge temperature / pressure and compressor amps. In cooling mode they lead to duct and air handler sweating (and then mold / mildew) and may even cause coil to ice up, another threat to compressor health. So, I don't install bypasses.

I limit multizone systems by tonnage. As a general rule 2-3 ton systems can support up to 4 zones. 4 ton systems approx 3 zones, 5-6 tons, no more than 2. Of course, all are two stage. I avoid zoning single stage systems.

If a house loads out to more than 4 tons and wants more than two zones, it gets two systems (Or a Carrier Greenspeed air source, whose lowest stage is 40% instead of 67%, but that's not a geo solution)

Since you are looking to spend serious $, have a proper load calc done. Also have in an energy rater auditor for a blower door test. The blower door test figure should be used in the load calc, replacing the construction tightness guess (loose, average, tight) in the load calc program. Consider also an infrared thermograph to identify heat loss.

A complete energy audit and load calc might cost you $1,000, but that would be money well spent instead of defaulting to a $15k guesstimate or some technician's wild guess as to required tonnage.

I wouldn't be suprised to hear Joe's guess is spot on - 4 tons subdivided into two systems. Don't fear 50-100 hours of auxiliary strip heat usage in winter in lieu of extra tonnage. net result will be quieter, more efficient, more comfortable.

We don't do bypasses either, for the above mentioned reasons. At the very least, it will make the system very inefficient. If the technician is even talking bypass, he does not understand the concept of making a heatpump run efficient, and how not to put extra stress on the compressor.


Option # 3 is BS as well, your load on the loop does not increase just because you are putting more heatpumps in, or make them bigger. They will just cycle more, but the heat extracted and put in your house will be similar.


Yes, you need a load calculation to determine how much each zone requires. Have that done and post the results here.


Waterfurnace has up to 6 zones with its variable speed heatpump, where the compressor can throttle down to 15% if only 1 zone is calling. But do the Manual J first. How many boreholes do you have?

OK. I will try and contact somone to come do the load calculation. I believe we have 6 boreholes but not sure. I'll have to go back to original papers and look. Once I get results from the calculations, I will post them. Again, thanks so much for your assistance. So is the consensus going to 2 smaller units?

You are killing the compressor due to the load you're putting on it and due to the refrigerant leak.

The load you're putting on the compressor is due to poor ductwork not carefully sized for the zoning you have in place (requires some particular expertise), the mere presence of a bypass duct (kills an ECM motor in addition to the compressor), and lack of corrective zone balancing actions.  The result of these 3 problems is causing inadequate airflow and at way too high or low temps.

It's not surprising you've gone through 2 compressors so far, and an imminent evap coil replacement.

The counsel above from docjensr and engineer is some of the finest you can get on this forum.  Certainly getting a Man J analysis and a blower door test will provide all the information needed to do a full re-design for your HVAC system.  The resulting actions will certainly give you the best 'bang for the buck' to correct your situation.

It's cold outside though, and thus, given the description of your problems, you may need to take immediate action if you're broken / shut down.  If so, I would do 4 things right away:
0) find an installer that can competently handle the next 3 listed suggested actions
1) go straight to the WF unit described above - it can handle severe zoning situations as what you have.
2) remove / turn off the bypass damper
3) get the zone balance motors reset to ensure air flow through the evap coil (not the rooms) is adequate / not excessive (a good installer will know how to measure the air flow through the coil and measure the External Static Pressure across the ECM motor) in all possible zoning situations (will result in some loss of HVAC efficiency and some loss of precision of room temp control, but will preserve the longevity of your equipment, particularly your compressor and evap coil)

This action is moderately expensive but it's one that accommodates your condition that you can't fix or replace any ductwork except what's in your mechanical room.  It also fixes all of your current broken equipment without any 'throw away' money.

I don't believe the above immediate action suggestions is a winning solution if you don't have someone who knows what he/she is doing.  Not having access to ductwork repair / replacement makes the airflows tricky for how you're now set up.  If you don't have someone local, you may still be better off finding a WF person that you bring in at your expense.

Going to 2 units seems excessively expensive to me - strikes me as a 'sledge hammer' approach.  This is going to require you to first spend 'throw away' money to replace your compressor and evap coil, and get damper motors balanced to avoid continued damage.  All before you've spent a lot more money on the redesign.

WRT loop capacity: your capacity needed is dependent on how much heat gain/loss your structure has.  If your current equipment, while operating very harshly to its components, is providing adequate heating/cooling (BTU/hr or BTU/day), then it doesn't seem that your loop field needs attention.  IMO it's not a 'top 5' item to look at relative to your other challenges.

The person who suggested needing to expand your loop field as part of adding more equipment to your system doesn't understand some fundamentals of HVAC system engineering.  While the person may have good expertise installing stuff specified and designed by others, I'd be very cautious using this person for system re-design and equipment selection.

Hope this helps.

Best regares,

Bill

Posted By DJ23 on 06 Jan 2013 08:23 AM
OK. I will try and contact somone to come do the load calculation. I believe we have 6 boreholes but not sure. I'll have to go back to original papers and look. Once I get results from the calculations, I will post them. Again, thanks so much for your assistance. So is the consensus going to 2 smaller units?

No, not 2 units. A better thing to bail you out is a unit which can modulate down to lesser capacity when your smallest zone calls. Right now there is only one unit on the market, Waterfurnace 7 series with Intellizone 2 zone controller. If you just repair your compressor you are not fixing your problem, it will happen again.

Posted By DJ23 on 06 Jan 2013 08:23 AM
So is the consensus going to 2 smaller units?

Not if the installation can be made to work well with one unit.

We have two units since our house was designed with two distinct areas that each unit serves.  Geothermal was a retrofit for us.  There was no good way to join our basement and attic trunk lines.  Generally, two systems would probably be more expensive than one.  Two systems offer a backup (in some parts of the house) in case one system fails, but I wouldn't install two systems for that reason only.

I agree with all remarks made since my last post.

If one unit can be made to work properly, then it is most likely the most economic solution. I haven't dipped a toe into Waterfurnace 7 waters, but that may be a viable solution.

Most of my projects involve going from two units to one, but it is vital to get the load, zoning and airflows correct as all above have written.

I don't think you ill find 2, 2 stage units cost more than 1 WF variable. In fact I think you will find they are much less expensive. But as has been mentioned. Design must come from the load calcs, so we are guessing til then.