I am looking for advice on optimizing results from our decision to install a GSHP to heat and cool (actually, control humidity levels, for the most part) in the house we are building in western NC.  The house is situated on a SE facing slope at about 3000 ft. in an area which averages 5500 HDD.  The Manual J calculation performed by our energy auditor prior to building called for total heating with outside air of 29,213 Btuh and 14,538 Btuh total cooling, or1.29 Tons based on 70% sensible capacity.  We had a separate Manual J done by the HVAC contractor -- I do not have access to that as I write this.

The decision was made to install a Climatemaster Tranquility 27, model TT-026, vertical loops, and a desuperheater.  There will be an UltimateAir ERV (200 DX).  The ducting is in progress, the unit is on-site, although the weather has not yet permitted well drilling.  

What approach should we take to take best advantage of what we have already committed to to be comfortable and to keep our energy use to the lowest practical level?  I have been concerned about the choice of water heating device, storage tank if needed, and the practicality of pre-plumbing for possible solar thermal.  I am also not sure we will have the humidity control we want without unnecessarily low temperature settings in the summer.

The household is 2 retired adults.  The house will be our full time residence, hopefully for the rest of our lives, so we are operating on the assumption that we will be in the house for at least 20 years.  The house has 1437 sf of conditioned space, R-30 walls, R-50 roof and Serious 925 windows, differentiated for orientation (although only SHGC of .3 for the south facing windows, so sun-tempered instead of passive solar).  The water use appliances have been selected to be very efficient in terms of water (and energy) use.  The mechanical room is 104 sf (conditioned), with 10 ft ceiling.  The house is all electric (5% lifetime discount), with a propane generator for back up.

Can you help?  I have read and re-read the posts on this forum which bear on this and am still unclear as to the best route forward.  Thanks for your input.  

2highcover,

You're really going the extra mile with your house. As an building science and HVAC consultant, I applaud your efforts!
I have the same ERV, a GSHP and a pretty well insulated home in a similar HDD climate. Your worries are well founded.
When you start looking at the performance specs for these units, even those with two stage compressors, you find that for much of the summer, the air conditioning will be very oversized leading to poor dehumidification.
There are some smart thermostats that try to improve the situation through the use of humidity sensors, and that can help some. You may also be able to run during the summer at a lower fan speed, which helps draw more humidity out. But really, when you're that oversized for cooling, it can be very challenging.
In my case, and you're not going to like this, I installed a Fujitsu 12RLS mini-split heat pump. This tiny but super efficient unit dramatically improved my home's comfort during the summer. In fact, I barely use the GSHP during the summer as the mini-split does the job so well. And, in fact, the performance is very close to that of a GSHP.

I'm sure some of the other pros on this list will have other ideas, but I just wanted to share what actually worked in my own home.

2HighCover, those windows sound pretty cool but I heard they are way off the charts for budget building. Can you say ballpark what it costs for an average window?

I'm a homeowner. Go with the lowest cycles per hour (CPH) thermostat setting that you can be comfortable with (temperature swings may be greater.) There are several benefits to reducing CPH including slightly better dehumidification and slightly better efficiency due to less system cycling. Some of us have noticed improved DSH hot water production.  Compressor longevity may be improved too.

A buffer tank is not needed if you have an electric water heater, but get one if you want the best efficiency out of the DSH and don't mind the additional leak potential and space requirements. If you get a propane water heater (you mentioned all electric, but I'm mentioning this since propane is available), you will need a buffer tank. Marathon electric water heaters (for a water heater or for a buffer tank) are great, but expensive. They have low heat loss and a lifetime tank warranty. I recall reading that they may not be best suited for solar though.

I would get the ATP32u04 thermostat that climatemaster sells. It, along with your cxm board, has smart humidity controls.

Have you looked at Climadry?

This is my first query to the forum and I am so gratified with the thoughtful (and speedy!) responses. Thank you!

tinoue -- I looked at the Fugitsu mini-split you recommended and it looks impressive. If it should come to that, we would probably need a multi unit model. In our two years in the area, the first being the third year of a drought and the second an unusually wet El Nino influenced year, we have not felt uncomfortable due to humidity. My husband has guitars so he pays close attention to the humidity levels they are experiencing. The levels in our unimproved 60s rent house were very high last summer, 70% and more. That being the context, we will probably be monitoring performance in the new house for at least a year or two before attempting to solve a problem we may not have. With my question(s) I am trying to make choices now which don't unnecessarily complicate or make potential solutions much more expensive to carry out.

geome -- It feels like I know you, given all the posts you have made on the topic of buffer tank or not. The info on the thermostat setting is new to me and I will definitely try that approach.

Are you familiar with the Marathon buffer tanks specically designed for solar applications? Since it looks like our DSH will be helping primarily in the 5 month heating season, I have been wondering if solar thermal panels oriented for optimum summer performance would cover us for DHW the balance of the year. (I guess I should ask that question elsewhere on the forum.) Anyway, we are seriously considering a Marathon water heater, a 40 gal would be plenty, with a buffer tank. What size the buffer tank has to be is another question, given the potential for solar thermal later. We do have some limitations given the size of the mechanical room.

heatoftheearth -- Thanks for the tip on the thermostat. Our HVAC guy has specified a Honeywell thermostat YTH9241C1002. I will question him about your alternative.

engineer -- You, like geome, have authored so many of the posts which have been helpful to me. Thank you. Yes, I looked at Climadry. The HVAC guy's answer was, as I recall, that it is not available for a 2-zone system. I will double check with him as that conversation was a while back.

Just wanted to add that our decisions are clearly influenced by both the available federal tax credits and the very generous North Carolina incentives which essentially mirror the feds at a 35% rate. Getting our GSHP for in effect less than half the upfront cost, along with our long time horizon, makes our situation a bit different from many others It gives us some flexibility to consider options which are more efficient and/or durable, even if more expensive at the outset.

2highcover, I only have experience with the non-solar Marathon with desuperheaters. You may have seen this page already, but here is a link to Marathons solar application page.
http://www.marathonheaters.com/cons_solarapps.html

It mentions that storage temperatures exceeding 185f will void the warranty. That must be what I remember reading. If sized and designed properly, this may not be an issue. There are solar people here that have posted, but you may be able to get more responses in the solar section of this forum.

When you say that a 40 gallon water heater will be sufficient, are you basing this on your experience with a gas water heater? Desuperheaters aside (since they only generate hot water when the geothermal unit runs), recovery rates of electric water heaters typically are not as high as gas water heaters. We compensate for this by having a large water heater with greater capacity. I like engineer's philosophy on water heater and buffer tank sizing (should be made a sticky in my opinion.)

Is your thermostat a 9421? If so, get the optional outdoor temperature sensor. In addition to you being able to see the outdoor temperature on the thermostat (pretty neat), it will allow you to set an auxiliary heat lockout temperature. If you set back at all (even a few degrees), or plan to make any manual changes to the set temperature, I think this feature will more than pay for itself within a few seasons.

Our HVAC guy has specified a Honeywell thermostat YTH9241C1002.

See also: YTH9421C1010. That's Honeywell's product number for the
full kit -- including TH9421C thermostat, equipment interface module,
and the outdoor temperature sensor that geome mentioned.

MSRP is about $510, but the online "street price" is $220-ish.

geome, yes, I had seen the Marathon solar application page, but revisiting it, I have just realized that this tank has a heating element as well. I had thought that a buffer tank was just a holding tank with its heat source being the solar or DSH or whatever. I guess this is not the case. I thought that the buffer tank would supply water to the regular water heater and that any outside sources of heat to the buffer tank would mean that more or less energy would be needed to reach the set DHW temperature. Clearly, I will need to spend more time in the solar section of the forum.

The sizing of the water heater was arrived at using Marathon's guidelines. The 4500w 40 gallon tank is rated at 52 (don't know what units) first hour and for 2 people who don't have to both shower before getting off to work, and with appliances selected for water and energy efficiency (internal heat elements), that seems fine. We will have the occasional guests but don't think that will be a problem. I need to find engineer's guidance on sizing.

You are right -- I meant 9421. The outdoor temperature sensor sounds cool indeed, not to mention the possible advantages you list. I will follow up on that.

Looby, thanks for the specifics. I will talk to the HVAC guy tomorrow. This is so timely. these changes should be easily made.

http://www.dehumidifierexperts.com/...uct=112860

The link above is to a whole house dehumidifier which can be ducted into any exsisting duct system including geothermal



http://www.amazon.com/Honeywell-YTH...B001O48A3U

This t-stat outdoor temp sensor , and remote . will work great to controll both the heating , humidification , cooling , dehumidification .
The reason I like this set up is for cooling needs is because it realy ADDS 3 stages ( being just dehum , dehum plus first stage , and dehum plus second stage )
its about as close as you can get reasonably in a residential situation to variable speed (ish) comfort . also a little cheaper and less visable then the mini-split
( which I also realy like and install all the time )

just another thought

Water heater first hour rating unit is gallons. The figure can be approximated by adding the tanks capacity and the additional hot water it can generate in an hour. The first hour rating for a typical storage electric water heater is its capacity plus about 10 gallons, so a rating of 52 for a 40 gallon tank is reasonable.

My sizing advice is as follows: Size the primary heater for your household's hour of greatest hot water use. With just two occupants not requiring long back to back showers 40 gal / 52 recovery sounds fine. Then size the buffer for a typical day's hot water use. This gives the DSH all day or all night, depending on whether heating or cooling season, to build a day's worth of hot water. DSH works slowly, increasing the water temp in a buffer tank only 5-10 degrees per pass and completing no more than 1-2 passes per hour of operation.

I happen to have met with a Rheem / Marathon rep at ACCA Tampa. I remember him describing the solar package, but not everything he told me. I do remember him saying that in a typical solar app solar water is brought in using one or both heating element inlets, and the problem with that is that the ports aren't reinforced enough to take the mechanical loads of attaching pipes. In the solar package those openings are reinforced.

I don't remember if the solar package has two, one or no elements; I'd think at least one would be useful as a backup. In a DSH app the element(s), if any could simply be not wired, or if wired, only energized when DSH is inactive (during mild weather there is little heating or cooling) AND company shows up demanding showers, baths, laundry etc. Its a quick way to add hot water capacity for infrequent use without the larger standby losses of a bigger tank.

I have the Honeywell Prestige Thermostat that geo fan just mentioned, but I don't have a dehumidifier. I use the dehumidify with air conditioner feature. I need to experiment with this feature a little more in cooling mode. It seemed to work sporadically in auto mode, but it may be fine in cooling mode. I didn't think of this until the end of last summer. It is basically an overcool feature where the cooling temperature can be set to cool up to 3f below the set point to reduce humidity (or at least make it a bit cooler and more comfortable.)

If you get a Prestige, get the color display. We have one color and one black and white. No comparison between the two. The wireless sensor works very well. We have it in a tree.

Check out http://www.prothermostats.com for pricing too (I almost bought from them.) You may or may not need the remote wireless sensor. We have it and it works well. Don't drop it. :-)

2highcover, even though appliances may have internal heating elements, they my still be plumbed to a hot water line and use DHW. Our dishwasher is plumbed this way. In the event of insufficient hot water, the dishwasher's heating elements will turn on to bring the water to temperature at 100% efficiency. In my opinion, it is better to include, at least in your buffer tank, enough capacity for these appliances. That way, you may get efficiency over 100% water heating efficiency due to DSH and any solar water heating contributions.

If plumbed to a cold water line, yes, the internal heating element of the appliance will turn on, and this won't effect the buffer tank or the hot water heater load. But heating of the water will be limited to 100% efficiency with the heating element in the appliance.

In general, I like to go a "little" larger on things to play it safe due to possible calculation errors, unexpected contingencies, etc. Nothing worse than having to buy a replacement if the original item doesn't suit your needs (or having to live with something that you aren't completely happy with). It keeps me comfortable over a wider range of inputs. Of course, cost needs to be considered as well. I'm not saying that this is the case with your tank sizing. With our single tank setup, we deliberately up sized our tank to make sure it would work as we desired. For us, there wasn't much of a cost increase going with a larger Marathon due to their pricing structure.

Try calling NJ Sussex Power and Light for pricing. I remember reading that they have good Marathon pricing, although I have not checked into this personally. Shipping cost may be a factor.  Let us know how you make out with everything. :-)

Many of the GSHP manufacturers have a dehum feature in the dip switch on the unit allowing for lower fan speeds doing this coupled with the over size coils would increase your humidity control. One thing to consider is if you do not use the A/C on your GSHP you lose out on the free hot water from the desuperheater. This more than likely will provide allmost all of the hot water for two retired people. using electric for hot water heater and not running the desuper heater would be an unfair trade off when installing a ductless split.
If humidity is a problem an inline dehumidifier from Therma Stor or other manufacuters is a great item to install for dehumidity assurance, they are very effiecient to operate, a better investment than a ductless split which only can cool one area not the whole house.
If you have desuperheater on the GSHP, take advantage of the free hot water from it by using the GSHP for Cooling