The attached chart shows the output of the desuperheater on your unit under the HWC column.   Basically you get between 1500 and 4000 btuh of hot water heating capacity when your heat pump is running.

When you are cooling your home,  this is free heat.  If you don't put it into your hot water,  it goes back into the ground.

When you are heating your house,  your are getting this heat about 1/4 the cost of heating the water with propane.

You could realistically plan on saving at least  50%  maybe 75% on your hot water heating bill.

Hope this helps

How much would you have to pay for the desuperheater?

Geodean,

Thanks as always.

What happens when the heat pump is "maxed" out in stage 2 during the coldest days of the year. Will it still output heat to the water reservoir?

Tuffluck,

I believe a total of $750 - $350 for a water heater and $400 for the desuperheater. If the savings is as shown in the Climatemaster data sheet, the cost may pay for itself over the years.

I will look at the data more closely.

Best regards to all,

VK

Yes.

The function of a desuperheater is to take some heat  out of the super heated freon before it goes to the air heat exchanger,  hence  the name desuperheater.

So the water always gets a portion of the heat before the air is heated for the house.

So on days when your heat pump runs the longest is when you get the most hot water.  If your heat pump is running 24 hours a day trying to keep the house warm, it might make sense to turn of the desuperheater and send the heat into your house instead.

How much does propane cost in your area?

VK,

Most unit will turn off the desuperheater pump when 2^nd stage of the compressor is called for.

You may want to look at the Marathon brand water heaters by Reem. They are low heat loss tanks. With my desuperheater and the Marathon 85 gallon water heater, the electric elements almost never need to turn on during the winter months.

The efficiency of the tank-less systems is a little deceptive in my opinion. They never take into account the air drawn from the inside of your home to use for combustion. This has to be replaced with unheated air from outside. Take into account the btu loss of this replacement outside air into your home is much like leaving a window wide open in the middle of winter. You will see the biggest savings by switching to the desuperheater and a low loss water heater.

Climate Master and Hydron do not turn off the desuperheater on 2nd stage. Which units do you know of that do this?

Thanks again, Dewayne.

I own my own propane tank and so I get a discount. But the last time I checked prices ( in January 2008) I was being quoted a price of $2.40/gallon.

Eric,
Thanks for your input.

I already own a Bosch tankless heater. It currently takes in air from my basement but when I have it set up with the desuperheater, I will make sure that the air for combustion is drawn from the outside. It is not a bid deal in my case because just a few months ago, I used to have a high efficiency propane furnace that was drawing air from the outside. I made sure that geothermal installer left the PVC line available for air intake for the hot water heater. The flue gas from the heater will exit the house via Z-flex lines.

On another forum HVAC installers have been recommending the Marathon water heater as the reservoir to which the desuperheater loop gets connected and the resutling heated water gets fed to a tankless water heater.

Marathon water heaters have a life time warranty, which is great. But the price is a bit much when you are only going to use it as a holding tank.

Best regards to all,

VK

The incremental (extra) cost of a Marathon tank over a standard electric water heater tank will likely never be recovered over the lifetime of a typical system. I have a 3 ton Waterfurnace Envision in the process of being piped to an 80 gallon GE 12 year warranty waterheater as a holding tank. I looked at the Marathon 105 gallon units but the additional cost (double +) couldn't be justified.

A 2nd 8- gallon GE water heater will serve as my primary hot water supply.

While comparing fuels beware that a gallon of propane ( ~4 llbs / 92,000 Btu) compares poorly against a gallon of fuel oil ( ~7 lbs / 130,000 Btu). In some localities it even compares badly against a KiloWatthour (3413 Btu), depending on costs of electricity vs Propane.

There's been much ballyhoo regarding tankless water heaters avoiding the standby losses of a standard storage tank water heater, but the reality is that standard electric storage water heaters are or can easily and cheaply made to be 95% or more efficient.

A gallon of propane burned in a conventional center flue domestic water heater (~60% efficiency) is a particularly miserable combination. Tankless units improve the math somewhat, but it is always required to compare fuel cost per unit, Btu content per unit, and heater efficiency to reach an informed decision as to what to choose.

Hot water from a desuperheater is cheap in winter and free (or better) in summer, assuming proper execution with a dedicated preheat tank. Without a dedicated preheat tank a desuperheater is nearly worthless.

By 'free or better' during summer I mean that a properly executed desuperheater can actually slightly reduce summer cooling costs by removing heat from, and thus decreasing head pressure and current drawn by an airconditioning compressor.

Engineer,

The above maybe correct for you, but not for everyone.  Some folks have an incredible deal on the Marathon if they check with their utility company.  Here is an example.  TriCounty Electric Company

Even without the super deal from the utility some folks can take a credit on their taxes for part of the cost.  There are many other advantages to this tank as well.  The fact that it doesn't have an anode rod makes it great for use with well water. 

I'm glad to hear your system is working well for you. 

Regards,

Eric,

That is a great rebate from the utility company. With that rebate the Marathon water heater could cost less than what I would have to pay for a standard water heater. I wonder what is the driver for a utility company to offer such a good rebate - what gain could they possible get?

Unfortunately, I live in SE PA and our utility company does not offer such rebates.

Engineer,

Your point is well taken about propane and tankless water heaters. However, I am stuck with propane and that is why I went with a geothermal system.

Several years ago I invested in a tankless water heater. Now all I have to do is buy a storage tank for my desuperheater.

Best regards to all,

VK

Engineer,

Could you please help me understand how a preheat tank helps with the desuperheater?

Thank you.

This has been explained several times on this board. Do a search for desuperheater and you can read all about it.

I 2nd the motion.

Engineer,

You mentioned having two 80-gallon tanks after the desuperheater.  What is the capacity of your GHP?

I am considering a three-ton dual-stage Envision and I wold like to use my existing 66-gallon heater as a storage tank.  How should the powered tank be sized relative to the storage tank?

Thank you.

My Envision is an 038 2 stage (nominal 3 ton), though so far I've kept stage 2 locked out and meet cooling setpoints on days as high as 94 Deg F, which are 'design' days. I probably could have gotten by with the 2.5 ton, but my builder urged me to oversize by 1/2 ton in case I ever lose my open loop artesian well water (enters at 70 deg F) and have to resort to a closed loop system whose entering water temps would be in the 90s, substantially reducing unit capacity. I took his advice. The 3 ton unit is the most efficient size, and the thermal mass of my ICF house increases runtime in the wee hours of sultry nights, substantially improving dehumidification without true 2 stage operation.

Powered tank should be no larger than necessary to meet household needs at peak time of use, typically when multiple showers are taken at around the same time. My 80 gallon powered tank may be too large, but it was cheap ($400 with a 12 year warranty) and I wanted to be able to accommodate house guests and a future 3rd bathroom, big master bath soaking tub and future teenagers taking long showers.

Oversizing the powered tank incurs slight penalties in efficiency - energy factor in the low point 90s rather than mid point 90s owing to larger surface area losing more heat.

Powered tank can instead be a tankless unit. I don't particularly favor them for reasons I've described in other posts, but they have their advantages of small size and efficiency.

Preheat tank should be as large as feasible, but ideally at least as large as needed to hold a day's use of hot water. The reason for this is to fully connect periods of heat recovery (late afternoon during summer, late at night in winter) with next day's periods of peak hot water use. In other words, I don't want inlet water to the powered tank to have missed out on the previous day's desuperheat whether it be during a hot summer afternoon or a cool winter night. Undersizing the preheat tank will cause some inlet water to the powered tank to not be preheated, somewhat defeating the purpose of the system.

66 gallon is probably a reasonable size for preheat on a 3 ton. The Cadillac tank would be a Marathon 105 gallon tank, but payback time for one would likely be decades, if ever.