Domestic Water Heating Idea...

JJ_4

Others have probably thought of this before...but here goes.  I am going to replace my steam boiler in the next 2 years.  In conjunction with this,I will replace the water heater; currently a cheapo State from HD (but it has lasted 13 years so far!). 



First, I like the idea of a side arm tank, but can't see pumping the sometimes thick, brown stuff water through a side arm heat exchanger (my pipes are almost 90 years old, with the exception of the wet condensate line that was replaced last year...which has reduced the "thick, brown" factor quite a bit).  Still, I think the pump would probably be problematic and a maintenance issue. 



Secondly, I see that many of my boiler choices have indirect coils available.  However, this is not the most efficient system...especially to fire a boiler in the summer (mine is typically dormant from April thru October).  



So, I am thinking of a hybrid (and later a "double hybrid") system.  This system would use the indirect coil in the boiler and be connected to a Marathon high EF electric water heater. In the winter, when the boiler is cranking I would pre-heat the supply water to the Marathon and minimize the electric coil usage. I am hoping this could be done without a pump; just from inlet cold water pressure, which is pretty good in our city.



So, what about summer?  Well, it is not as critical, as hot baths and hot showers are lower frequency, but.....this is where the "double hybrid" idea comes in. I would connect in a Geyser (<a href="http://www.northrdt.com/GeyserManualv1_9.pdf">http://www.northrdt.com/GeyserManualv1_9.pdf</a>) or equivalent heat-pump water heater to provide summer pre-heat (and I suppose it could also run in the winter too in parallel with the boiler indirect; as the heat pump would love all the lost heat off the boiler in the boiler room).   



I see this as a two phase project, due to cost.  1st the Marathon with the indirect. Then later, add the Geyser. 



Anybody try this?  I found one article on-line using a Marathon with the Geyser...have to connect differently because of how the Marathon drain connection is set-up vs. standard heaters.  I also see that Marathons are commonly used with solar...that is esentially what I would be doing....storing as much hot water from the boiler source as possible and using the electric coils just for back-up. 



I know some will say...stick with gas, electric is expensive, but I am also planning on saving for and installing a 4-6KW solar PV system....so some added electric usage should be offset; particularly in the summer months. 



Thanks for the sounding "wall".  Any thoughts are welcome.  JJ

Big Ed_4

Depends

Depends on your energy costs , your usage and location... Seeing hat your system is steam ,I have to assume you reside in the North or live high enough when energy for heating will be higher then for domestic hot water ... Unless you tell me you have 6 teenage Daughters ... I am also assuming you burn oil for heat , for the fact most of your boiler choices offer an " indirect " coil ... Or what we call a domestic coil .



Now it depends cost of your energy , which would be cheaper , then offset the cost by the efficiency of the equipment ...



Say electricity comes in cheaper then oil then why burn the extra oil to preheat water ?



If oil comes in cheaper then why only burn oil when there is a demand ? You can use the coil like a side arm , you will need , one bronze pump on he domestic side to build up a cheap storage tank ... Which the heat pump can also heat up as well ...



Now what is your hot water load ? ... Which is very important question before deciding on a hot water heater... Say If you do have Six Daughters , they all take showers one after the other , Then BTU input and storage should be your main concern .?. Say the household runs one shower in the am and one later in the afternoon then recovery or input is not that much of an issue, But storage may ... Size it to the biggest load ... it may be a 75 gallon tub or a 20 min shower with a 5 gallon flow rate ...

JJ_4

Thanks for the reply Big Ed...

Thanks for the reply Big Ed.  Though most of your assumptions don't apply, but your advice is well taken.



I live in Denver.  Gas is my heating fuel.  My boiler choices are from the major players (Burnham, Smith, Slantfin, W-M, etc.), and, while I would like to go with a power burner (ex. Smith G8 or Slantfin Intrepid) I will probably end up with a conventional burner with EI.  Cost, burner maintenace complexity, and burner noise (from what I understand) are all factors.  The size is SMALL...my measured load is right at 200 sf of radiation, backed up by heatloss calculation of just under 50K BTUH.  I am looking at boilers that meet the measured radiation, though most are in the 217-280 sf range. 



My biggest savings (once the $ are put out) will be in the boiler replacement.  It is currently 174K input and probably 50% efficient (1981 Smith G200 type), and I only need 70-100K input (with an increase to 80-82% efficiency).  I am guessing that the old boiler was sized based on the original coal boiler..because even though I eliminated some radiation (and added insulation)it would still have been way too big. 



I'd just like to find a way to compliment this improvement with something other than a 50-60% efficient gas water tank water heater.  I like the EF factor of 2.0+ for the heat pump water heaters....as this takes some of the sting out of electric rates vs.gas rates.  I will not put in a tankless heater.  I've used them before and they are not adequate, and are a pain in the neck (to put it mildly).  So this is why I am looking at efficient tank options.  Location precludes sealed combustion condensing gas units...except maybe the Eternal Hybrid, which I could locate on the 1st floor because of its size.



There are 4 of us, 2 women, 2 men.  We are careful in timing our showers, though I don't use a stopwatch!  Women are typicallly 15 minutes, men 5 minutes.  Showers are typically not at the same time, as we only have one bath (for now).  1 load of dishes per day.  4 loads of laundry per week.  House kept at 68-70 degrees.



My gas costs are $.912/therm, electric is $.09/KWH.  The boiler and water heater are gas.  I have 3500 Watts of electric baseboard, though I have thermostat/controllers that match current to demand, rather than on/off thermostats. This baseboard doesn't turn on much, as the space is connected with the spaces that have steam radiators and there is enough convected warm air that reachs the basboard space that the setpoint is satisfied.



Other high demand electrical items are frig, dryer, dishwasher, and a seldom used oven (range top is gas).  I have an evaporative cooler, which breaks about even summer for winter with the electric baseboard. 



To your question: "...why burn the extra oil to preheat water ?"  The idea is I wouldn't be burning extra fuel to preheat...just scavange off the boiler (just like people try to do from gray water) to capture some of what is already being heated for the steam heat. 



Thanks again...I'll work it out with my heating pro. Just wanted to see if anyone else had taken the same approach.



 

Big Ed_4

Scavenge

Only gas boiler I know of that can be ordered with a coil is the Slant fin ... Burnham three pass steam boiler "Mega Steam " with a Riello gas burner would be my choice of heating boiler , A efficient boiler with some input adjustments ...



With the hot water , using a high efficiency gas hot water heater tank in which you can add a heat pump ...Would be one way,



Buying a Hot water coil for the Burnham and hooking up an aqua booster would be another ,

Big Ed_4

Scavenge

Only gas boiler I know of that can be ordered with a coil is the Slant fin ... Burnham three pass steam boiler "Mega Steam " with a Riello gas burner would be my choice of heating boiler , A efficient boiler with some input adjustments ...



With the hot water , using a high efficiency gas hot water heater tank in which you can add a heat pump ...Would be one way,



Buying a Hot water coil for the Burnham and hooking up an aqua booster would be another , Since your hot water has a scattered demand ....



Your tank size ? 15 min shower with a 2.5 shower head flow rate = 37 gallons / use a 40 gallon tank minimum ...