Desuperheaters and GT 2x3.5 ton systems

15 years ago

We're installing our GT system now, and I paid for two desuperheaters for hot water generation. I talked to the plumber who said you don't need a storage tank, and it's useless with the hot water generators. I talked to the HVAC guy who said the desuperheater only raises the pre-water-heater temp by 5-10 degrees. The company is a certified GT install and repair company, so I'm getting a bit confused.

I've read on this forum and other sites that you should have a storage tank equal to a full day of hot water usage. Should I have an 80-gal storage tank (well insulated) and an 80-gal powered heater hooked up in series? I read that the outlet from the desuperheater goes to the cold water intake on the storage tank, then the hot water output from storage goes to cold water intake on the powered unit.

In summary... I need a large storage tank to make the desuperheater (I have one on each unit) efficient, right? What size tank should I use?

I'd appreciate any guidance that can be quickly offered. Plumber is at the site now!

Sort by:Oldest

Comments (7)

zl700
15 years ago
You absolutely need a tank to circulate from the desuperheaters (Ht Exchangers) with a pump and a storage tank, most often a solar or electric water heater with an element for backup. The superheaters have minimal capacity and are not capable of supply hot water instantaneously, beside compressors donÂt run 100% of the time.

The size of tank should be estimated by your max use or peak drawdown. That would depend on your usage, lifestyle and hot water demands. Of course the bigger or more is better as once the AC operation raises the water to a desirable and safe limit, it goes back to rejecting the heat outside. (save as much as you can afford to and have space for)

In your case, you may consider two 80 gal electric water heaters (one for each unit that is circulated between, stats set lower than rejected heat available and pipe the domestic hot water side in parellel to supply the home.
garymunson-2008
15 years ago
Here in central Florida I find a single 80 gal water heater is sufficient for hot water storage. We never run out. Regardless of the type of system (GT, air to air, air to water) the hot gas temp exiting the compressor is pretty much the same. The systems only differ in how they shed heat after it leaves the compressor. As long as the hot gas is at least 180 degrees (usually is more than that) a de-superheater works great.
Gary.
Related Discussions
Traditional Heat-Pump, Geothermal, or other?
Q
Comments (31)
Ah CT - here we spent $90 last month for 4000 sq feet - with just ASHP.... but that was mostly A/C (and lights etc). Are you still heating in CT? To respond to the previous poster. Geothermal works great in the South (just like the North) - its just that it is overkill most of the time. My audit suggested I'd save $300 a year with geothermal but that was based on a reference house - it was down to about $100 compared to HE ASHP. Try to get $100 a year to ever payback - sure it saves money but you could save more clipping a coupon a week without the $20k upfront cost. How is this thread still alive? The savings of geothermal compared to oil in the North is amazing. Compared to ASHP in the South - it is pennies. There is an ad line that says installing geo is like taking 2 cars off the road. They must be some pretty efficient cars.... Unless you are comparing to oil in the North. The average car driving 12,000 miles a year costs about $2000 in energy (20 mpg at $3 a gallon). The average house uses less than that for HVAC. Cost is not the only concern but there is nothing clean about gas in a car - at least electricity can be clean.... CONC: Insulate and use geothermal if you can do horizontal loop or live in the North and your alternative is not NG. And drive a hybrid and/or right sized car. And don't use incandescent bulbs for lights on frequently.
...See More
Geothermal Payback
Q
Comments (10)
The price for 12 tons of HE LP gas heat plus electric AC was around 30,000. It was York equipment (3 heater units and 3 outside AC units) and this included everything except some some zoning on the second floor and quiet vent fans which I added later. The cost for the GT system - same BTU output - was 45 grand - Econar Geosource 2000 equipment, 3 GSHPs (2 - 3 ton and 1 - 6 ton). The people who did the work have been doing GT for over 20 years and they did a great job. We had an initial issue with the 6 ton unit, but after that was rectified, the system has performed flawlessly for over 1.5 years. The GT price did not include the cost to dig the horizontal pit (the excavation costs) but it did include all the pipes, pumps, plumbing etc. This is where I ran into the glitch. The initial cost for the pit was 2500. When it was done - 17 grand! The actual cost to dig the pit, move the mountain of dirt from point A to Point B and then Back Again was around 10 grand. The cost for 1 foot of stone dust at the base of the pit (to protect pipes from rocks) was around 3 grand and the cost to rent the track hoe to move the massive boulders was around 4 grand. Hopefully you would not run into this issue - I built on the side of a mountain and hit a lot of large boulders. SO the total delta cost was around 32 grand for the GT system, 30 grand when I took the tax credit. I have an 9100 sq ft house (5800 on 2 levels + 3300 sq ft basement that is conditioned but only partially finished). It costs under 4000 per year to heat & cool it. My peak electric bill in the dead of this past winter was $450 BUT over 100 of that is lights/steamshower/ etc. So my cost to heat this monster was 350 peak. LP would have been 2x that at the price per gallon this winter. I plan on living in this house for 15 to 17 years. The GT will certainly pay for itself by then but I estimated about 10 years to breal even.
...See More
Hot Water on Demand
Q
Comments (26)
One of the concerns that has been bought up several times in this thread is that tankless heaters use a lot of energy. This is quite true, but also misleading. While regular tank heaters use a moderate amount of energy and require a fairly small electrical connection, the elements in them are running for a long time, many hours a day, and not just when the hot water is being used, they also switch on frequently to maintain the temperature of the stored water, which in itself consumes a fair bit of energy considering the thermal mass of all that water, and that it's constantly loosing energy through the tank walls. Tankless heaters use lots of energy and have suitably big electrical connections, but only run for very short amounts of time. There are genuine energy savings to be made with them, it would be mistaken to assume they actually use more just because they have a large Kw rating and need a huge fuse. A little often does add up to much more than a lot infrequently. Also, with a few exceptions, tankless heaters do heat the water more efficiently. The ones I've seen average about 80% or more, which does compare well against a lot of the tank heaters available.
...See More
Geo Thermal heating - your eperience
Q
Comments (31)
Forgive me if I don't weigh in on the political info above. Instead, I'll share our geo experience. We live in Minneapolis, MN, in a 1950's rambler. Approx 1900 FSF on the main, with 1500 FSF in the basement. We had a 28 year old forced air furnace with a similarly old central air unit in the back yard. There was a disconnected fungus farm (humidifier) on the ducting, and the house was usually bone dry in the winter. We were considering a GSHP when we learned of the 30% Federal tax credit, but then the installer we had picked (out of 4 who came and gave us bids), told us of a 35% State rebate (using Federal stimulus package funds), and we realized it was a no-brainer. We spent about $35k for our system, including a Venmar 4100 Hepa ERV that I installed myself, a Honeywell Tru Steam 12 gal humidifier that I installed, a new 200 amp Siemens power panel, with a 100 amp sub panel for the dedicated heat pump only electrical meter), a new 95% efficient Lennox furnace (backup and air handler), a 4 ton 2 stage envision waterfurnace heat pump with de superheater and 55 gallon buffer tank (which I had to plumb in 55 copper fittings to sweat!), and 3 vertical wells 250 feet deep. The system is controlled by a Honeywell IAQ 8000 stat system. Our costs, as stated were about 35k. We received a $9400 rebate check from the state (they didn't allow any rebate on the gas furnace part of the costs, as it wasn't GEO), a $600 rebate from our power company, and a $300 rebate from the gas company. We *should* see a full 30% tax credit on the full system cost when we do our taxes this year. I hate math, so I'll use rough numbers--We should see around $20k in rebates, meaning we'll have around $15k out of pocket. A new conventional system would have cost somewhere between $10k-$15k for an identical high efficiency furnace and central air unit. Again, assume I could have found a contractor to install a conventional system for 10k (doubtful, IMHO), that means I paid a $5k premium for a ground source heat pump over a conventional system. Given that I'm only 40 years of age, and plan to stay in this house as long as I can, we'll see that $5k premium back fairly quickly. According to the Waterfurnace calculations (which may well be optimistic), our averaged monthly utility bills should drop from $246 per month down to $64. Obviously, the short payback on our system is possible largely as a result of govt subsidies. Much like the continued existence of many of our nation's banks and car makers.
...See More
funnycide
15 years ago
The best is to have a separate HW storage tank. Usually it's a electric water heater without power. 80 gal is better than 40 or 50. It comes down to cost and I don't know if the extra cost of an 80 makes sense. A desuperheater may only produce 3000 btu of heat. That is why it's not great just to pipe it to a single water heater. The elements in the tank will quickly heat up the water and the desuperheater won't get a chance to do it's job. With a preheat tank the desuperheater can run all day or all night and heat up the 50 (or 80) gals of water.
zl700
15 years ago
Actually on a 3 ton system with an entering water temp of 67 degrees the capabilities are up to 22,000 BTU's an hour recovery. As we know, the AC may run anywhere from 1 to 24 hours a day depending on many factors, mostly outdoor temps.

ThatÂs about 40 gallons at a 60 degree rise an hour possible (without a calc)

As poster stated they have 2 desuperheaters on site, it can be difficult to control circulation to storage of one tank to prevent cooling of hot water generated although not impossible. With two systems, two tanks make more sense. Of course you could go with a no circ system but exchange would be near non-existent if there was no DHW flow.

A water heater as part of storage or separate is still required when AC is not running or often enough to meet DHW demand.
hoosierdoc
Original Author
15 years ago
As a further question... we were going to have a hot water circulating pump running in the house. Is that not a good idea with a desuperheater and storage tank system?
funnycide
15 years ago
Z- I am not familar with a model that can produce that many btu's from the desuperheater. Can you give me that make and model so I can look into it?
zl700
15 years ago
Sure

http://www.turbotecproducts.com/EPhome.html

Download the energy savings on the desuperheater.
With my on-demand gas heater as the final heater, my payback with self-install was 15 years +

Not doing that!

They make a titanium condenser heat exchanger with 2" PVC connections I am considering for my swimming pool. Once I calculate in this $ along with install accy's such as head pressure control, relays, stats, and piping if it is worth it those 4-5 months the AC runs on occasion and wished the pool was warmer.

I just need to finish calcs and weigh ROI.

Desuperheaters and GT 2x3.5 ton systems

Comments (7)

zl700

garymunson-2008

Related Discussions

funnycide

zl700

hoosierdoc
Original Author

funnycide

zl700

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Desuperheaters and GT 2x3.5 ton systems

Comments (7)

zl700

garymunson-2008

Related Discussions

funnycide

zl700

hoosierdocOriginal Author

funnycide

zl700

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

hoosierdoc
Original Author