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DHW configuration

I have a NTI Tft 155 boiler that is set up for indirect DHW with a 67 gallon Lochinvar tank. It works fine and we always have hot water, but I wonder if I have the sola controller configuration parameters optimally configured to save gas. My bills have been the same as with the two older 40 gal gas water heaters plumbed in series, but based on the attached image and the fact that it only runs briefly when the tank needs to be reheated, I was wondering if I could tweak things to make it use less natgas by either having it modulate lower for DHW cycles or by adjusting the hysteresis parameters. Any advice for tweaking parameters for summertime DHW heating? Many thanks in advance.


  • Zman
    Zman Member Posts: 6,965

    The first thing I would be looking at is your standby heat losses. Do you have an uninsulated recirc line? Maybe a bad case of gravity thermosyphoning?

    You should not be seeing those kinds of cycles during times when no hot water is being used.

    As far as adjustments go. You can manipulate the settings a great deal if you have a thermastatic mixing valve to stabilize the outlet temp and protect from scalding.You could for example turn the boiler on when the tank temp is at 120 and off when it hits 140.

    The On/off differential will maximize the cycle length. Lowering the boiler temp during  a call for hot water will allow the boiler to condense during part of the DHW cycle. Without condensing, your 95+% boiler is just a 84% model.

    The first step is to get control of the heat loss. I think that is where most of the waste is.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 15,004
    heat traps

    either the heat trap nipples or Sioux Chief Heat Trap loop will eliminate thermosiphon.

    Or if you have a recirc add thermostat, timer, and insulation.

    I think Carl has it right, your heated water is moving energy dollars from the tank, somehow.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265

    IMO (worth little or nothing), if or when you pipe two smaller water heaters in series to get more hot water, all you do is make it ONE bigger water heater, a combined total of the two. If you had 2-40 gallon gas water heaters piped in SERIES (into the first and out the second) you have a 80 gallon water heater. Because the first water heater does all the work and the second one hardly ever comes on. So, you are heating DHW with a 40 gallon water heater. Now, you are heating a 67 gallon indirect which is a larger heater. Any efficiency's you might have seen are lost with the larger tank.

    If you are going to twin (or have multiple) tanks, they must be piped in parallel with some form or parallel reverse return. If two tanks, they MUST be piped with equal connections between the two tanks. As close to being perfectly balanced as you can get it. 3 or more MUST be piped as parallel reverse return. First in (cold), Last out (hot).

    If you use a "Mixer" which I think that all water heater storage tanks should have, (for personal reasons), you need to install a quality mixer with internal checks. Some come with 1/2" recirculation ports. But they ALL recommend that they be installed as "Heat Trapped:. Which means that the centerline or outlet of the hot water inlet of the valve be a minimum of 12" BELOW the cold water inlet of the tank or source of hot water.

    If your gas bill didn't take the expected drop, it might be because you are heating a bigger tank.
  • icesailor
    icesailor Member Posts: 7,265
    Another thing (on hot water)

    Another thing.


    When you ran two tanks and only one was doing all the work, if it was gas (you said it was), it was probably a 35,000 BTU input burner, doing all the work. With Beer Cooler boilers, run on ODR, they won't be running in the Summer except to make hot water. In March, they might be running at some low temperature to heat the structure. 110 degrees so you get lots of that elusive efficiency through condensation. That won't get the soap out of the hair. So the control strategy switches to "priority" and kicks the controls up to "High Limit" to ONLY run the indirect. Which is just another heating zone as far as the boiler is concerned.

    It has been my LONG experience with oil boilers and tank less coils (an indirect coil in a different location) that a operating control set at 140 degrees that tries to keep the boiler water at 140 degrees at all times, (to stop internal boiler fire side condensation) will make all the hot water needed. You can get it faster by raising the operating/Low Limit control. But the control doesn't "see" the DHW tank as an additional zone, just part of the boiler. Which the boiler is trying to maintain temperature.

    If you can lower the high limit setting on your beer cooler boiler to 140 or 150 degrees, so that if it gets a priority call for hot water, you don't need 170 or 180 degree hot water to do the job. In my long practice of using 50 gallon storage tanks (electrics NOT connected to power. I don't want to confuse anyone) and 140 or 150 Low Limit/operating settings. I NEVER have had a complaint during the summer or "off"  seasons.

    Try lowering the high limit for the time and see if it doesn't save fuel. IMO, no matter what you do though, you are trying to "P" up a rope. Leave your computer on all the time and add up all the other continuous power things in your house, and you can pay for a new Data Logger.

    I had a customer for years. Some work was done on the house that involved electricity. He called me up one day in the middle of the winter and said he was getting a high electric bill but all the power was off. He asked me if I had any idea of why and could I look at it. I went there and sure enough with the main 200 amp 40 circuit panel off, the meter spun. There was an outside disconnect. Shut it off, and the meter stopped. Turn it back on. Turn of the main on the 40 circuit panel and all the breakers, the meter spun. There was another 20 circuit in the back for the boiler and garage. But the main panel was in the kitchen in the main part of a two story 3 bedroom gambrel house. While walking around, trying to figure things out, I noticed (I do that) that there was a small green bar showing on the blank microwave screen. I unplugged the microwave and the green bar went away. If I ran the Microwave, when it was done and I reset it, the bar reappeared. When I unplugged the microwave and looked at the outside meter, it was stopped. When I made the green bar appear on the Microwave, the meter spun. I unplugged the Microwave and the problem went away. Never underestimate the cost of "Ghost Loads".

    Like Comcast. My Cable Box makes a noise like a fan running even when it is off. Unless I unplug it. How much is THAT costing me? Then, the Association pays for Cable. They switched to Comcast. I already had internet phone and Internet access with them. They made me take a new cable access box to handle the phone and Internet also. Of course, they FU'ed up the connection and the installer didn't believe I knew what I was talking about. Until he came to find out I was right. It still isn't right, but that's another issue. There's a light that is always flickering on the Modem. Sometimes at 2:00 AM, it goes out. It doesn't matter if I am connected to the Internet. There was an article in the Palm Beach Post about complaints that Comcast was using new Modem Routers as "Wi-Fi Hot Spots" and anyone could access the Internet through private customers routers. So Comcast can get a chunk of the Smartphone Wi-Fi traffic at my expense? Some people I've known would be on Pogo Sticks (jumping up and down) if I did something like that without asking. The same ones that when a bill is over 60 days, they finally pay the amount on the first bill but never pay the interest. Once you cash the needed check, its considered "Paid In Full". Try THAT scheme with the Wall Street Crime Syndicate or the local Bankster you do business with.
  • Zman
    Zman Member Posts: 6,965


    It is great to see you are enjoying your retirement. I really am enjoying your posts I am just not sure how they pertain to the the original question.

    What is it raining in Florida?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • extremetemps
    extremetemps Member Posts: 4

    Thanks. I'll try setting the upper limit to 140. Cool(er).
  • icesailor
    icesailor Member Posts: 7,265

    The original post mentioned a boiler and using two gas water heaters that sounded like they were piped in series because one hardly ever ran, and the other was doing all the work. That an option was being considered to use a 60 gallon indirect. All well and good. Then, it got in to heat traps and etc. My comments were related to the fact that the two water heaters, properly pipes, held more hot water etc.


    Some have no idea how far we are advanced on the North about heat loss/gain and how to heat of cool a building.

    I don't think that I have seen a "normal" heated building in the North, be under rated/under heated. Most of us understand and know how to deal with heat loss in a structure like we might discuss the latest sports team.

    When it comes to cooling and heat gain (I always thought it was the same only in reverse), it's advanced rocket science. Done by FM.

    As far as Florida rain, the Summer is the "Rainy" Season. Someone once said that in Oregon, it rains all the time. In Texas, it rains all at once. Same with Florida. Only South Florida is one of the lightning capitol's of the world. So, if you really enjoy big loud boomers, come on down. Every morning and every afternoon. When it comes down, it comes down like Hell in a bucket. A mile away, not a drop.
  • extremetemps
    extremetemps Member Posts: 4
    edited July 2014

    Here's what it looks like with the setpoint at 140. First image is hourly, second one daily.

    I should note that in the daily image the first two cycles are with setpoint 180 the second two 140 and the hourly image was from this morning.

    Less area in red should mean less energy consumption, right?
  • icesailor
    icesailor Member Posts: 7,265
    Outside Logging:

    In my (easily disputed) opinion, you are using some form of data logging that is using the outside air temperature compared to the temperature of the boiler as if it was winter time and you are trying to heat a structure.

    I think that when you do what you are trying to do that is to compute your hot water temperature, it is counter productive, With a indirect heater, the system and real world sees the Indirect as a heating zone and you are trying to heat the structure with it. Because you have no heat loss to the outside, but only through the incoming cold water and how much you heat it, it just can't compute. If it is heat and you can develop a known heat loss against a known constant, what you are doing, won't show you savings except to show you when the burner runs or not. With domestic hot water, the issue is to get the amount of hot water you need in a given amount of time. The amount varies with demand. The more water you have coming out of the hot water side to get the comfortable water temperature you need, the faster you will run out. The hotter the hot water, the more cold you need to get it to the temperature you need for comfort. And you won't be running out of hot water in the same hotter tank.

    If you had a Mod-Con, and you ran it with DHW priority, you could probably set the high limit priority to 140 degrees in the Spring, Summer and Fall and have lots of hot water. If you have to drive from point "A" to point "B" that is 40 miles away, it will take you 2 hours at 20 MPH and one hour at 40 MPH. But you get there just the same. How long it takes is up to you.