Electric water heater with timer and thermostatic mixing valve

pinkeng

Solar Enthusiast
Joined
Aug 5, 2021
Messages
19
Location
northern california
Makes sense. I assume you added external insulation around the sides and top. One other thing to reduce heat loss if the distribution piping is above the water heater is to put a U bend in the hot water supply. If your hot supply pipe is hot above the water heater you can/ will lose heat that way. Adding a 12" drop and then back up will prevent thermosyphon. Hot water is less dense so it rises to the top. A 12" deep/ long U or S bend stops that. Just FYI.
 

SolarPrep

Solar Addict
Joined
Jul 15, 2021
Messages
229
Just a couple of comments to add to this old thread:

Here in the Midwest, we have a lot of limestone, and very hard water. That limes up water heaters over time. We do 2 stage filtering of all water coming in the house, except for toilets, and outside spigots. I do run toilets through a separate mineral filter.

We use the 20" orange colored housings (high temperature filters) on boilers, solar water tanks, water heaters, etc with a cheap pump and either a timer to turn it on, or just a manual switch. Cycling it periodically helps keep the fluids clean, and prolongs life of all devices.

Use a watt meter to check how much current is used by those old fashioned mechanical timers.

I've seen people scrounge a cheap or free tank, and hook it up just to let water come up to temp of the house, before going into the water heater. Our ground water is about 50 degrees here, but I have no way of ascertaining if it absorbs more heat from the house, than it saves from heating that same water up with your water heater. I suspect it does save energy.

If you are shopping for a three way valve for any device, check the specs for pressure drop through the valve. I used to use Honeywell, but switched to Caleffi after realizing how much extra energy it requires, especially if you are pumping water. If it is just City pressure it may not make a difference.

A small pump on a hot water recirculation loop does save energy in most cases. I picked up a brand new bronze TACO pump at a local thrift shop for $10 that is 1/40th hp. Perfect.

Insulate all tanks. Pay attention to piping insulation.

Consider building a hot water drain heat exchanger with scrap parts, and hook it up to things like showers. Source material through a local scrap yard, and check out designs on "Build it Solar".
 

12VoltInstalls

…myself everything do I…
Joined
Jan 18, 2021
Messages
4,423
Location
Vermont
I have no way of ascertaining if it absorbs more heat from the house, than it saves from heating that same water up with your water heater. I suspect it does save energy.
Energy savings is a wash in winter heating regions.
Dollar savings comes down to what you heat the living space with: if the water heater is electric, generally electricity costs more per BTU in most locales than other energy sources. Energy costs from least cost to most cost per BTU is usually coal, wood, wood pellets, oil, propane, with electricity the highest (in many regions electric heat is not much more costly than propane). (Natural gas is a ‘flyer’ as some regions the cost is very low while in others it is higher in cost/BTU than oil. Electricity in some places close to hydro plants electricity is cheaper by a lot. So ymmv)

In summer, pre-warming water ahead of the water heater is cost-free, while in winter the dollar savings will be whatever the difference between your heating fuel cost and hot water heater fuel cost is, per BTU, if any.
 

magic8192

Solar Enthusiast
Joined
Feb 26, 2021
Messages
69
I have a few comments about using a hot water heater with 180 degree thermostat, a mechanical timer, and a mixing valve.
The things I have changed since originally hooking it up. I put scald guards on the showers so the kids don't accidentally get hurt if something goes wrong. I originally wired the timer to the lower thermostat. I changed that and wired it up to the upper thermostat and it now controls both thermostats. You have to change both thermostats anyway because I originally only changed the bottom and the top thermostat would trip on high temp.

This is the biggest energy saver I have done. I averaged about a 20% drop in my power bill with this. I have a 50 gallon tank and I have enough hot water to stay above 120F for 2 days with the normal showers/dishwasher runs.
 

SolarPrep

Solar Addict
Joined
Jul 15, 2021
Messages
229
Energy savings is a wash in winter heating regions.
Dollar savings comes down to what you heat the living space with: if the water heater is electric, generally electricity costs more per BTU in most locales than other energy sources. Energy costs from least cost to most cost per BTU is usually coal, wood, wood pellets, oil, propane, with electricity the highest (in many regions electric heat is not much more costly than propane). (Natural gas is a ‘flyer’ as some regions the cost is very low while in others it is higher in cost/BTU than oil. Electricity in some places close to hydro plants electricity is cheaper by a lot. So ymmv)

In summer, pre-warming water ahead of the water heater is cost-free, while in winter the dollar savings will be whatever the difference between your heating fuel cost and hot water heater fuel cost is, per BTU, if any.
12voltInstalls: I would assume that your comment is accurate. I didn't refer to my own situation, because our hot water is via integrated heat exchanger off gas boiler, with additional solar hot water panels. It seems bizarre to be considering going back to electric, based off PV, but right now it looks like gas prices are going to take a serious hike upwards.

If I was building a new home today, I would build smaller, and super energy efficient. Lots of PV.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
12,152
Mechanical timer - to turn off during peak rate hours, and that's the savings on bill?
Following a power failure you have to adjust time or would operate during wrong hours.

I got some Harbor Freight digital timers. They have a rechargeable battery.
They are for 120V and light weight. Used to use for espresso machine, but failed so now use mechanical. I do use one for an electric water heater that is running on 120V rather than 240V. Power relay would be needed for 240V or higher wattage.

It seems bizarre to be considering going back to electric, based off PV, but right now it looks like gas prices are going to take a serious hike upwards.

How about picking up an electric water heater and plumbing it as a pre-heater or post-heater? Last one in line has to maintain temperature.
Could enable electric heating when gas prices rise, or when producing surplus electricity that doesn't get good net-metering credit, or during low-rate times.

Ideally would have a single tank with both heat sources. If gas + electric, that would have gas flue as a heat-loss path. Since yours is heat exchanger, might be able to plumb a heating element into pipe, optionally enabled while pump running.
 

keepsake

Solar Enthusiast
Joined
Jan 17, 2021
Messages
240
How would I go about calculating the runtime for a taco 1/40 hp circulation pump ?
I am at 28 deg latitude with a AE-40 collector.
40 sq ft surface area.
It moves about 1.8 gpm
Collector volume 1.22 gallons.
My roof sensor is open circuited. Not worth the climb at my age to deal with. I just fixed a resistor to make it 'think' its always 180 deg F on the roof. My automation knows what the 'pv' production is at anytime.
So I can automate when the pump runs and stops.
If I cycle it every 5 minutes, at peak sun, do I run it 1 minute, 2 min ?
I can even adjust runtime based on 'pv' hitting property at any given moment.
 

pinkeng

Solar Enthusiast
Joined
Aug 5, 2021
Messages
19
Location
northern california
Here is what I would do. Get a inferred non contact thermometer (Amazon or any hardware store). install a ball valve on the discharge of the pump and set the ball valve partly closed. Measure the supply (Colder) and return (hotter) pipe and adjust the valve open or closed till you have about a 20 degree F difference in pipe temperature. adjust valve with small changes starting either way at 1/2 closed, till you get a 10-20 degree rise say at 11 AM ish.

Then let the pump run full time till the tank is at 140-160 degrees F. Supply coming off the bottom of the tank (Not cold inlet). Why not cold inlet. There is a small hole in the top of the dip tube to act like a poor mans vacuum breaker when first filling the tank. Pulling suction from the inlet will pull some hot water out with it.

Note you will want a relief on the discharge of the panel piped to safe place / gutter as non flowing water in a solar panel in summer will produce steam, which you really don't want. If you have an 80 gallon hot water tank or two 40 gallon tanks your probably ok. one 40 gallon tank might be too small for a 40SF panel.

Ballpark assume 200 BTUH's per SF of solar hydronic panel. There are calc's you can do to get the exact number. But as it varies by the same things PV's deal with, 200 BTUH's per SF is a good ballpark. It's what I used 40 years ago after perusing solar design manuals for engineers. A bit more BTUH in the south, a bit less in the north USA. 1 GPM with a 20 degree F delta (difference between supply and return) is calc's using GPM*500 (Constant = weight of water and time)*DeltaT =BTUH (DeltaT is the difference between supply and return). To heat one gallon 100 degrees F in one hour = 1GPMx500x100 or 50000 BTU. This is for USA. Rest of the world uses KW.

Really A differential thermostat control is what you need. It automates the pump run time. It's not to spendy.
 

keepsake

Solar Enthusiast
Joined
Jan 17, 2021
Messages
240
Have an 80 gal tank. Also have a mixing valve.
fyi -- about a week ago I 'caught' the system pump on at 11 pm. Pump hot. Must've been running continuously. Next day I found open circuit on the roof sensor. Conclusion was that at times circulation at night was actually lowering the water temp !! I have a contact thermister sensor right now on the metal hot water fitting on top of the tank. Very sloppy sample as hot water usage brings about good sensor reading. Lack of running hot causes sensor to skew.
 

keepsake

Solar Enthusiast
Joined
Jan 17, 2021
Messages
240
fyi --
def StopTacoPump():
if tasm[22].powersw.get() == True:
StopTasmDev(22)
hvaclogger.info("cycle: turning off taco pump")

def CycleSolarCollector(): # every 5 minutes
pv1p = sensors['pv1Pwr'].get()
if pv1p > 4000: # was 2000
# if tasm[22].powersw.get() == False:
StartTasmDev(22)
rt = int((pv1p-3000)/40) # was -3000/80,-0/100 -- 5 kw >> 50 sec
hvaclogger.info("sun good: turning on taco pump: %ss"%(rt))
cron.OneShot(delay=rt,doStart=True,onTick=[StopTacoPump])
 
Top