Multi-zoning driven by true variable speed air conditioning. Is it finally here?

[lleo]

Installing ground loops is expensive, especially in dense hard rock, which conversely has the best thermal conductivity. Sandy soil on the contrary has very poor thermal conductivity, thus requiring much longer loops. If water table is high and water wells have high flows, you can do open-loop ground-source heat-pumps, pulling water from one well and dumping it into another, but there the ill effects of untreated water take a toll on equipment. While it is easy to (over)size an A/C or heat-pump system, typically with geothermal they can get undersized, like when the installer is not familiar with ground tempertures where they do an install. If they assume a 55 degree ground temp and in the summer that gets up to 75-80, you will understand that such system will not cool well. Correcting a mis-sized ground loop is difficult as the loops have to be symetrical, or else the rules of fluidics will direct flow differetly and the net effect can be even worse.
For sure, if one has the money and hires a knowledgeable installer, the loops can outlive the house and work well, typically over 50 years.
Paired with a photovoltaic electricity generator a ground source heat-pump can be trully green, but currently only at very high capital expense.
Where I live with a lot fraking in nearby PA and NY, gas is cheap(er) Given how much is estimated to be done there, this likely to outlast me. It is also my perception that we will not make any significant progress toward alternative energy/uses until we burn the last drip of the fossil fuels, so the sooner we do the faster we may do the transition...
Sorry for the off-topic, I'm ready for the weekend, enjoy!

 

[IndyMike]

I had not noticed that lleo was in NJ.  I have a sister in the Princeton area - the rock structure would certainly be an issue for a ground source system.
 
My data points for installing ground loops are based on the fact that we regularly drill wells in the area at 200+ feet and think nothing of it.  Again, the suggestion was not for my area.  I can point to numerous studies that show that residential GSHP systems are a negative in MI, MN, and WI vs forced air gas.  This is for both cost and emissions.
 
In areas where cooling costs predominate, I would think this would be a good trade - unless the soil structure makes it prohibitively expensive to install.
 
My cost /therm for ng was $.27 in Aug and $.35 in July.  Just for grins I searched for historical pricing for the area.  It does very wildly : https://www.nipsco.com/docs/default-source/gas-tariffs-063011-docs/commodity-cost-of-gas-history.pdf
 
Can't explain why pricing hit $1.72 /therm in July 2008.  Not normally a high demand period.

 

[Automate]

Can't explain why pricing hit $1.72 /therm in July 2008.  Not normally a high demand period.

 
That was before fracking was common and the corresponding explosion of US natural gas production.

 

[IndyMike]

That was before fracking was common and the corresponding explosion of US natural gas production.

 
You nailed it.  Gas prices were directly linked to crude prices back then.  On July 3, 2008 crude spiked above $145/bl.  How quickly I forget recent history...
 
Sorry for the diversion

 

[NeverDie]

I notice that back in January Trane announced a 27.5 SEER variable speed air conditioner, the XV-S (http://www.achrnews.com/articles/125609-thursday-jan-23-2014-trane-introduces-ultra-high-efficiency-variable-speed-system).  That's quite a performance jump over it's existing 21 SEER XV20i.  Unfortunately, so far it's vaporware, as I don't yet see it being offered as an actual product on the Trane website.  

It's now more than two years after it was announced, and it's still not on their website.  In fact, as far as I can tell, Trane still isn't offering anything even close to that. I hate to say it, but in retrospect it seems like that "announcement" was just BS.

 

[ano]

It's now more than two years after it was announced, and it's still not on their website.  In fact, as far as I can tell, Trane still isn't offering anything even close to that. I hate to say it, but in retrospect it seems like that "announcement" was just BS.

You can probably blame VW for that. There is getting to be far more scrutiny over these wild SEER claims because in actual use, they come no where near it and people are starting to check now.
 
As someone who just installed a new TRANE unit a few months ago, I'd be VERY careful with those "Ultra-Efficient" units.  I got my HVAC installed by one of the best installers in the area, and he said to save your money on these. Not only do they very seldom even approach the numbers you see, but when it comes repair time, the price for controller boards and compressors can be 10X of standard parts.  (Yes that is 10 times the cost.)  You will never get the cost back. And i might add that I am in AZ, where ac efficiency is probably more important than where you live.  Today 16 to 17 SEER is about the best compromise, and that efficiency will only be possible if they perfectly match the blower to the coil to your duct work.  Most installers don't even do that well.    Spend more than a two stage unit and you are only throwing your money away.  I went with a single stage. 

 

[NeverDie]

Closing the loop:  Today our two single speed R-22 Trane HVACs were replaced with two Puron Lennox variable speed XC25 systems,  At least so far I'm very happy with it.  It's much quieter, both inside and outside the house.  For example, If I stand right next to the outdoor condensers when they're running, they're actually quieter than my neighbor's air conditioner that's running across the yard.  That makes a difference, because my home office, which is near those condensers, is now much quieter.  It's generally much quieter running inside too, in part because much of the time it's running at a much lower speed, and also it ramps up slowly instead of going from zero to full-on all at once almost like a canon, which is what the old single speed Trane did.
 
It allegedly keeps the temperature within 0.5 degree of the setpoint, and so far, though I haven't rigorously vetted that claim, subjectively speaking that seems about right.  We can set a "feels like" temperature target which accounts for both humidity and temperature.  We purchased the upgraded S30 wifi thermostats, which can be controlled by smartphones and tablets.  I'm not sure yet how that will connect with my home automation system, but it seems at least theoretically possible, whereas I had read on this forum that some of the other thermostats/systems were very difficult to integrate.  It even has geofencing.  I didn't add any extra zoning at this time, but the existing hardware can actually handle 4 zones per system.  So, we'll see how it goes, and if we conclude we need additional zones, then we'll add them down the road.

 

[NeverDie]

Interestingly, running for longer cycles at slower speed using the variable drive also seems to even out the air temperature throughout the house more.  That's a pleasant surprise.  I hadn't really expected that.
 
Since the air handlers and ducting is in a hot attic, it stands to reason that running longer cycles will be picking up more attic heat, even if we aren't feeling that inside the house.  On the other hand, running at lower speed might conceivably result in less leakage, which might offset that.  I guess time will tell how much, if any, energy savings we actually realize from the higher efficiency system.  I'm not sure how I could do an exacting comparison, but it will nonetheless be interesting to do a rough comparison at the end of the summer.  Anyhow, our primary objective was to maximize comfort, and I do think we're much closer to that now than we were before.  Our old system had reached its end of life, such that it didn't  make sense to wait even longer for Trane to deliver on their announced system before replacing it.  My main regret now is that I waited at all!

 

[NeverDie]

Another thing that's interestingly different about the new system is the ability to set a humidification target in the range of 40-60% RH, inclusive.  Obviously, the lower the RH, the higher the actual temperature can be for the same "feels like" temperature.  I've set our target at 40%, but so far it hasn't actually gotten that low.  The question I have is: do I win by setting a low humidity target, because then the actual temp can be higher and thereby require less energy, or do I end up using more energy to remove the humidity than I save by being able to set a higher target temperature?   Anyone know how to answer that?

 

[lleo]

congrats to your new systems.
 
it will take a while until your whole house is dried out.
it also depends on the leakiness of your shell, how well the vapor barriers work.
If you cook a lot, bathrooms have no exhausts, clothes dryer vented in basement, water, humidity in basement etc. i.e. a lot of moisture source, you may not be able to reduce it significantly.
in my home, I face a revolt if I set the humidity at 40 %RH and temp 75. It feels cold to my family. we keep it at 78 and 75 after midnight.
My system has a dehumidifier only mode with automatic switching between cool and dehum. mode
To dehumidify-only takes shorter condenser runs at minimal capacity compared to serious cooling, so my intuition is that should save you money to keep humidity low. But comfort should be first. Keep it on for a day or two at a set temperature and see how much it uses. If I recall it correctly, your system reports energy use , so should be easy to compare.

 

[NeverDie]

One convenient feature I didn't even realize was part of the system until my wife discovered it after the fact: from each thermostat, you can also control the other thermostat.  So, our downstairs thermostat can be used to set our upstairs thermostat, which saves us a trip up and down the stairs.  We could also do it from our phones, which we already knew, but we don't always walk around with those like some people apparently do.