There is no "not enough hot water usage" to justify a single tank setup. Either you use enough hot water, and you should go with 2 tank, or you have so little water usage, that you can skip the desuperheater at all and use a point of use or on demand electric. I re-read your thread and looked at the performance numbers. A 4 ton system with St. Louis MO weather data and your loads actually runs cheaper then a 5 ton system despite going slightly more into aux, because the 4 ton heatpumps run more efficient (better COP) than the 5 tons. You know what I would do: Call up the guy you liked most, assuming the references checked out, and tell them that you liked them most, but that he was much more expensive, and that you did not like him $4000 more. Ask him if he is willing to come down and match the others quote, and you have a deal. If he does not, go with the other guys. Simple. However, not matter what you do, insist on a 2 tank setup if you feel it is worth it with a DSH. Temperature and Energy logging by: Web Energy Logger Temperature and Energy logging by: Web Energy Logger Here are 2 system streaming data with "2 older folks household". As you can see, 3 ton systems, and not a single time in the last 24 hours was the DSH not contributing to the hot water generation while the system was running.
docjenser, Thanks for the information and charts. I have pretty much come to the decision you suggested in your most recent post. I believe, after reading all the posts again, the 4 ton unit would be the better option with a second tank for the DSH and go with a 10KW strip. One question I do have, the supply line for the heat pump has to enter the basement and travel about 17 feet to where the existing system is located then back the same 17 feet to the water heater. Does this severely affect the efficiency of the system? There is no way I can move either the water system, holding tank and softener or the main heating/cooling system. Is there a way to effectively insulate the piping to avoid heat loss? Also, do all systems have some sort of monitor where I would be able to see the same info on our home that you supplied in the links? Thanks again. Like I said, if it was not for all the members here, I'm not sure where I'd be right now.
Don't worry about the header pipes in the basement. It is conditioned or semi conditioned space. Your installer will insulate them to avoid condesation drips. If I read right that one of your installers wants to circulate water between the buffer and the finish tank- NO, NO, NO. It will render the buffer tank useless. The monitoring system you asked about is a Web Energy Logger easily found by Google.
!7 feet are no problem for the source pipes. DSH should also be OK. Insulate all of them well. DSH only raises temp by 5-10 F, so loosing 50% is a big deal. WELserver is the way to go.
Ah.....when you said "enters" the basement I mistook that for header pipe, but yes DSH pipe must be insulated as well.
OK, first, what is the "buffer"? Is that the additional hot water heater that is not connect to power and is heated by the DSH only and acts as the input for the active hot water heater when there is a demand? Then, what is WELserver, a type of insulation for the pipes? The other posts I have read say 2 tanks (hot water heaters~~one active one holding is the way to go. The one contractor wanted to circulate the hot water in the active tank through the DSH. Said it would prevent the heating coils from coming on in the water heater. Since the DSH only gives me about 5-10 degrees of heating for the water, I guess I should plan to buy an insulation blanket for the inactive water heater to hold in what little heat I get. It almost sounds like the DSH isn't worth the cost, at least until energy costs skyrocket Thanks again guys..
Yes, the buffer tank is the additional hot water tank which is not active, usually a foam insulated electric tank without the heat elements wired (or at least with flipped off breakers). Web Energy Logger (WEL): Energy monitoring system. With all respect to your contractor, but this was a BS answer. The heating coils turn on when fresh cold water enters the tank and the tank temp drops below the setpoint. Since the DSH has little capacity and does not respond quickly, the electric heat element responds, heats up the tank with electricity, and then the tank is too hot so the DSH will stop making hot water. A waste of the DSH install. This is where a buffer tank comes in, since the DSH does not compete with the electric element which has much more capacity. Every time your the water cycles through the DSH it adds 5-10 degrees. So it brings your buffer tank to 70F, than 80F, than 90F and so one until it reaches 130F. That usually takes hours but is very efficient. No you take a shower, turn on the dishwasher etc, 130F enters the active tank (at least in the winter in my climate), and the electric heat element will not engage. Look at the charts I sent you the links for in detail, it shows the delta T between DSH in and out, the buffer tank temp, and how long it takes to bring it up to temperature. No need for a blanket, 2 inch foam insulation on regular tank is fine. DSH piped correctly usually well worth the cost, even in a 2 person household, especially with the help of 30% tax credit. Again, look at the performances I posted (WEL). It is just not worth doing it when you pipe it into the active tank which is kept up to temperature by an other source, usually the electric element.
Ditto everything DJ wrote DO NOT bother spending for the DSH option unless it incorporates a separate, dedicated, unpowered upstream preheat tank, ideally sized for a typical full day's hot water use.
Now I fully understand docjenser and engineer, Thanks for the reply and explanations. I think I fully understand now. FYI, the contractor that suggested circulating the hot water through the DSH instead of the holding tank is the same on who wanted to run 2 vertical lines down each hole. Think I'm going to eliminate them today. I am leaning towards the Waterfurnace with Climate Master running a close second. Waterfurnace is higher in cost but I like what I have read about them. Seems there have been some problems mentioned in posts concerning Climate Master. A couple more cups of coffee should help with the decision.
size of a buffer tank? I don't mean to highjack this thread, but I wanted to ask a question about the buffer tank size. I have a system running now with DSH option (2.5 ton FHP), but DSH is piped direct to the 80 gallon electric DHW tank. I now understand that this is not the proper (efficient) way to use DSH. I now want to add another tank. From a plumbing perspective it would be easiest for me to just add a new 80 gallon electric unit after the existing tank and switch the electrical wiring to the second tank, thus converting my existing tank to a buffer. My question is weather an 80 gallon tank is too big to be used as a buffer? Should I buy a 50 gallon to use as buffer and replumb things? Any thoughts? thanks Matt
I am in favor of a smaller buffer, not more than 50 gallons. 80 gallons is too much, it will not get up to max temp, stay below 100F most of the time. The question is what you want, a lot of water lukewarm, where you second tank needs to make up the difference no matter what. Or a smaller fast responding tank, which is actually warmer than the second tank most of the time, and even after a shower recovers relatively quickly?
LongshoreGeo, Not a problem and everyone's input has helped me make up my mind too. I'm going with a 50 gal. tank for the DSH which will feed my existing 80 gal connected tank. Now, if I can just get a morning to call the contractors.
DSH piping question I am getting ready to pipe in my buffer tank and I have a question about piping. The existing single tank was piped using a concentric fitting on the bottom of the tank - DSH in and DSH out both were piped to this fitting. Do you guys recommend using this fitting on the bottom on the new buffer tank or piping as per climatemaster schematics (water to DSH is T'ed into cold water supply on top of tank and DSH out water is piped to bottom of tank). I assume the second piping orientation will perform better, but I just wanted to get some other opinions. thanks Matt
contract signed a mailed Well, to everyone who has helped to guide me through the process, I have sent in the contract and I'm going with the waterfurnace system. Thanks for all the help and I'll update when everything starts. Not looking forward to tearing up our front yard but once everything is in and running I'm sure we will be happy with the results. Anything I need to pay attention to regarding the Waterfurnace system?
