[Greenbuilding] Max Temp Storage Water Heaters+TemperatureSensors

Thu Feb 10 09:33:26 CST 2011

You can get tankless heaters that run on 40 amps, certainly on 50,  
which will give you a hot shower.
Even better if you can pre-warm the water 10, 15* with a tank in a  
warm basement.
Clarke Olsen
373 route 203
Spencertown, NY 12165
USA
518-392-4640
colsen at fairpoint.net

On Feb 9, 2011, at 11:26 PM, elitalking wrote:

> Thanks for the responses for Max Temp Storage Water Heaters 
> +TemperatureSensors
>
> Steve Satow writes:
> Eli, this begs the question: if you are already replacing the water  
> heater, why not get an on-demand electric tankless system that  
> supplies water to the bathroom only when you want it?  More compact  
> than any tank so you can put it somewhere convenient and it would  
> eliminate virtually all the unavoidable standby losses associated  
> with a tank?
>
> My response
>
> I reviewed your suggestion for online electric on demand tankless  
> systems.  We are on the same concept of heating the water when it  
> is needed instead of storing it with standby heat losses.   
> Instantaneous heater with a low flow shower is likely the most  
> efficient way to go.  However, I am not ready to give up my hot  
> bath.  I found a range of amp size water heaters for Rheme as a  
> representative of the performance I can expect.  http:// 
> globalimageserver.com/fetchDocument.aspx?id=b125d219-d5f8-46c3- 
> ab02-5934e3043c7d
> The limitation is how much the water temperature will be raised  
> above the starting temperature at various flow rates.  If starting  
> at a ground temperature of 55F it would take a rise of 55F to  
> achieve 110F bath.  2.1gpm for RTE Model 13 will raise 50F.  The  
> unit requires a 240v at 60amp breaker.  This could work if I was  
> building a new house.  However, I have recently removed a heat  
> pump, making two wires already wired to breaker box available for  
> new service.  Installing a new line to breaker box is a significant  
> increase of effort.  I would like to use a 30amp (old compressor)  
> or 50amp circuit (old air handler with heat element backup).  The  
> preference is for use of 30amp wire that can reach the new location  
> next to tub.  I want to use 50amp circuit for new breaker box for  
> potential expansion.  However, with a junction box, I could use  
> that wire.
> My intention is to heat the water when it is needed, and not store  
> hot water that has to be reheated.  Instantaneous heaters fit this  
> concept.
>
> Perhaps water could be stored in a un-insulated tank that would be  
> warmed from 55F to room temperature of 70F.  That would then only  
> require a boost of 40F to achieve 110F.  RTE9 (220v x 40amp) can  
> achieve this with 2.2gpm flow.  In this case the tank would not be  
> insulated at all to use the room to preheat the tank.  Make no  
> mistake, this will take heat away from the room that must be made  
> up by the air heating system.  If heating with a heat pump, this  
> has COP of that system.  Currently we are primarily using wood  
> heat.  I am uncertain of the recovery rate would be for this  
> preheat tank.
>
> On this list I here that heat losses from tank or other appliances  
> are captured as a benefit for heating the house in the winter.   
> This is only a COP of 1kwh heat for 1kwh electric consumption.   
> This list knows that electricity generally takes about 3kwh of fuel  
> to deliver one kwh.  This limited benefit for heat loss only  
> applies in the winter.  In the summer the hot water heat loss is a  
> double liability.  If the house is cooled in the summer, the cost  
> of removing that heat loss is more than a kwh/kwh heat loss.  In my  
> case, since I removed the heat pump, it is not energy consumption,  
> it is comfort.  If I am replacing  room temperature water 70F with  
> ground temperature water of 55F, it will have a slight cooling  
> benefit for comfort in the summer.
>
> However, the main concept is to heat water up when needed and to  
> not store it.  In our current hot water tank location, we are  
> serving the kitchen and the bathroom that are separated by about  
> 30’.  The tank is immediately over the kitchen sink.  We would  
> sometimes allow the water to reheat while we took our bath.  As is  
> pointed out, the savings from the gradual lowering of temperature  
> may be negligible.  However, if that stored water is consumed in  
> the kitchen, then the heat loss is completely halted.  In fact when  
> ground temp water replaces the consumed hot water, the heat flow  
> reverses direction.  This is a preheat before switching heater back  
> on.  This allowed us some water for kitchen consumption.
>
> Our current approach is to separate the kitchen and bath to produce  
> hot water in those locations only when needed.  I do not consider a  
> slight delay at time of use to be an extreme hardship.  We will  
> heat up water for tea or coffee at the time of use instead of  
> storing continuously reheated water.  I think the instantaneous  
> heater would work well in the kitchen.  We currently use a basin  
> instead of the full kitchen sink which reduces the total water  
> needed.  I am considering plumbing a really small un-insulated tank  
> (1/2gal) with no intentions of storage to be heated by a induction  
> stove top.  In this way, I can within a few minutes have adequate  
> warm water for sink basin for dish washing water.  While washing  
> the dishes in basin, the heater can be quickly be re heating up the  
> next batch for rinsing.  In this way, we are continually resupplied  
> with hot water until we are done.  Then the induction stove top is  
> switched off and the small tank returns to room temperature waiting  
> for its next use with no standby heat losses.  Until I can get  
> something like that together, I am not averse to setting the basin  
> of water on our current induction stove top to heat the water.  I  
> have this list to thank for making me aware of this great fast  
> heating, efficient and very responsive technology.
>
> The instantaneous heaters can do this also.  However to be  
> instantaneous requires a larger wire.  Using an induction stove or  
> possibly a microwave (if someone can work through those issues) to  
> heat water on demand but not instantaneously, allows for a simple  
> 120v receptacle to meet the need.  This greatly increases the  
> flexibility to heat water at many locations.  This also avoids the  
> heat losses from long pipes that connect one central heater serving  
> the whole house.
>
> For us, the bathtub is the most demanding hot water use.  Perhaps  
> the hot water of a 30amp 220 volt instantaneous heater for hot bath  
> could be boosted to desired temperature by a circulating water  
> heater such as a whirlpool.  Is there such a product for heating  
> water in an open pool such as a tub?  This would allow for mixing  
> of creek water to supplement cistern water during draughts.  Could  
> this possibly be an alternative to pressurized water heater for  
> bathing?
>
> Long story short, heat only the quantity water needed at the  
> location when it is needed.
>
> Again, thanks for input.  I hope for more feedback.
>
> Eli
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