tankless water heater and solar

al128 · September 2008

Hi there,

what are my options concerning gas powered water heaters (wh) and a solar hot water system?

... I understand that there are some "smart" wh's that detect the temp of the incoming water and only add as much heat as necesary to take a shower(takagi, bosch) ... anybody any experience with them? how is it done .... modulating the flame?

do they work as advertised? ...

thx for sharing any thoughts
al

sawmill · September 2008

Re: tankless water heater and solar

I use solar hot water to preheat a small tank (17gal) that feeds into a Rinnai tankless heater.

It works great, any water preheat will decrease the flame needed to produce your selected temp. On sunny days it keeps the Rinnai turned off.

Hope this helps.

icarus · September 2008

Re: tankless water heater and solar

Almost all the modern (quality) demand water heaters will modulate burners as needed. Takaki, Rinnai, Paloma, and I believe Bosch control the output temps. The older style standing pilot units by Paloma (legacy series) don't modulate very well as they have no electronics to tell the temp. The units that plug into the wall for ignition like the Takagi TK Jr will modulate with computer control. Very reliable and very accurate.

Tony

PS On a personal note, I have used the Paloma legacy series for years with fantastic results. Off grid we have ~6 of them in various uses and they have NEVER failed. The down side is standing pilot and manual modulation, but they are bullet proof. They are also phasing out production of the legacy series, which is too bad.
For other applications, I installed and used several Takagi TK jrs with great results. Perfect temp control, and no failures in almost 5 years. By reputation, Rinnai also rates well.

I have had less good luck with Bosch. I think the technology is a bit behind, and I may be a bit jaded by early experience with the early ELM Aquastar from Bosch. I have an older unit that has been a bit of a problem, but most importantly, it came with metric plumbing fittings that were very hard to mate, AND, parts are no longer available, even simple routine items like thermocouples and water diaphrams.
T

Chuck46 · September 2008

Re: tankless water heater and solar

Ive been using a Bosch 125 with electronic ignition and have had no issues for 3 years
Chhuck

rickeolis · September 2008

Re: tankless water heater and solar

I'm on a Bosch 1600 that I installed about a year ago (propane) and am VERY happy with it.

System2 · January 2009

Re: tankless water heater and solar

Hi, 4 years ago I installed a new Paloma Wai Wela PH-28 COF at 199,900 BTU/HR and a second hand solar hot water water system that my friend gave me. I had to rebuild the hot water panels, but the system works fine. My thought was to heat the water with the solar panels and put it in a 80 gal. storeage tank during the day hours. The Paloma is used as a back-up to the hot water storeage, if the temperture of the storeage tank dips below 114* or at any point I set my remote keypad,the paloma to turn on and maintain the set temperture. The Paloma has a sensor on the inlet monitoring water temp. as used. I've cut back on my propane usage by 75% or more just by using this set up. Before this I had a regular 40 gal. gas water heater. Also I valved the system so I can use each hot water maker independently if needed.
Hope this helps!

Cariboocoot · January 2009

Re: tankless water heater and solar

I have an older Bosch with 'turbine' ignition; no standing pilot and uses no external electric to light.
As Icarus says, the fittings are metric but it came with adapters so once installed that isn't a problem. Getting replacement parts may be.
It has worked fine for many years now, but it does not regulate according to output temp: merely raises incoming water by 'X' degrees. Alright if your source water is consistent temp, such as from a deep well. Not so good if you're pumping out of a lake or stream.
If I had it to do over (and I'll have to someday) I'd 'tap off' a few watts from the inverter to run electronic controls and get truly regulated output temp.
The other advantage of regulated output is, of course, the ability to add direct solar heat when available and save propane while maintaining consistent temperature.

icarus · January 2009

Re: tankless water heater and solar

The problem with the new units is the electrical energy requirements. The Rinnai's use ~75 watts running, for the controls and the fans, and ~5 watts standby. I can't get a real spec on the the Takagi's but the new Palomas spec calls for <2 amps/120vac.

It would be an interesting to know if for example, a Rinnai or a Takagi would wake up an inverter when it called for heat. I would think not. I really don't want to be burning 60 wh just for standby, plus another 35 wh for running day in and day out. My propane savings would be tiny since I kill the pilot after the last shower in the evening and don't light it at least until the breakfast dishes. Another example of how loads grow with time, that additional 100wh would be 20% of my current total average daily load!

Tony

hillbilly · January 2009

Re: tankless water heater and solar

We bought one of the newer Paloma units two years ago, forgot the exact model number. I was kind of concerned about the power consumption 2amps at 120v is a big load for us. Turns out to rarely use that much power, and as for stand by consumption, as far as I can tell it's pretty much nill. It will NOT wake up our inverter though, and it sometimes can be a bit quirky and cranky... but for the most part we've been pretty happy with it. I think that average draw has been more like about 100watts running typically, not too bad considering that between my wife and I it's not really drawing power (or gas) for that long. As for waking the inverter, we have a single 13watt cfl light by the kitchen sink to turn on and wake the inverter, and lights and/or fan in the bathroom that will wake the inverter before turning on the hot water.

icarus · January 2009

Re: tankless water heater and solar

You took the words right out of my mouth! I was going to suggest a light switch near the shower or the sink! LOL

Still, 100 watts for 30 minutes is 50 whs, about 10% of my daily total. Living proof of how loads grow with time.

I'm going to keep my little PH6 going forever. I have spare thermocouples, water diaphragms,, since it is all stainless and copper, it should go forever! I kill the pilot for most of the day so that it really doesn't burn much gas on standby. The only bad thing is having the vent stack sucking heat out of the house 24/7. I would love to figure out a simple, fail safe heat activated stack damper that would open when it fired up.

Tony

BB. · January 2009

Re: tankless water heater and solar

That is why it is so important to measure actual power usage vs name plate ratings using a DMM or kill-a-watt meter.

By the way, there is another kill-a-watt meter that has an internal battery... For those people on off-grid power (where the inverters are not always running), the battery backed k-a-w meter saves the cumaltive readings, even during power outages (if I read the data sheet correctly). Has to have AC power in order to read the LCD.

-Bill

Bob McGovern · February 2009

Re: tankless water heater and solar

A bit late to this party, but....

I use the Bosch 125 BS with solar preheated water. It uses a strictly mechanical sensing-and-modulation valve. Generally works well, and certainly our propane consumption is very low. But like all these heaters, it is touchy about gas pressure/volume and about water flow rates. When it is bitterly cold and cloudy here, the outside regulator ices up and the shower doesn't get above lukewarm.

The solution, counter intuitively, is to turn DOWN the hot water. That reduces the flow rate enough that the burners can keep up, despite lower gas inlet pressures.

Oh -- and that's the only thing I hate about the Bosch. You lose 30% pressure in your hot line because of the coil-type heat exchanger. There's a temptation to jack up your main water pressure to compensate.

FL SUN · March 2009

Re: tankless water heater and solar

We have a Rinnai tankless using NG that has solar supplementation. I've got an 80 gallon non-powered storage tank that feeds into the Rinnai either tempering input water on low solar days, or keeping the Rinnai off on good solar days. It works very well to eliminate unecessary NG consumption. I have reduced therm consumption by 60% since going solar DHW.

I have 2 issues with this set-up. First, the tank is 15 linear ft away from the Rinnai so it "fires off" initially until the cold slug is replaced by the hot or warmer tank water. A penalty of a small amount of NG, and electricity consumption is the result. Due to things beyond my control, the tank cannot be moved any closer.

The other problem is taking showers when the tank temp and Rinnai setpoint temp are within 5 degrees of each other. (This would be in the 115 to 120 degree range for showering) The Rinnai cycles on and off at this threshold condition. They call it the "sandwiching effect", and it's very frustrating in the shower constantly adjusting the valve hotter and colder as the tankless fires on and off. The only way I've found to eliminate this is to set the Rinnai temp up 10 to 15 degrees warmer than the storage tank temp before we shower. This is not fully automatic, and operator error would lead to a disappointed customer in a "packaged" configuration.

It would be a great idea incorporate a tank temperature sensor integrated with a "Solar Rinnai" configuration option. It would automatically adjust the output temperature setpoint when the two temperatures are within 5 degrees of each other.

LucMan · May 2009

Re: tankless water heater and solar

FL SUN wrote: »

The other problem is taking showers when the tank temp and Rinnai setpoint temp are within 5 degrees of each other. (This would be in the 115 to 120 degree range for showering) The Rinnai cycles on and off at this threshold condition. They call it the "sandwiching effect", and it's very frustrating in the shower constantly adjusting the valve hotter and colder as the tankless fires on and off. The only way I've found to eliminate this is to set the Rinnai temp up 10 to 15 degrees warmer than the storage tank temp before we shower. This is not fully automatic, and operator error would lead to a disappointed customer in a "packaged" configuration.

It would be a great idea incorporate a tank temperature sensor integrated with a "Solar Rinnai" configuration option. It would automatically adjust the output temperature setpoint when the two temperatures are within 5 degrees of each other.

You could wire in a hot water temperature controller in series from the power plug to your Rinnai strapping the bulb to the hot water line from your tank. Set the T stat at 110 degrees cutout to start with and adjust from there until you get the desired HW temp at your shower with out short cycling unnecessarily.

tankless water heater and solar

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