Metering Domestic Hot Water Usage

Lightning wrote: ↑

Fri. Nov. 26, 2021 10:03 am

I also had an idea of a heat reclaim system. Turns out that other people have done it. The basic principle is to run your cold copper pipe thru a stretch of drain plumbing from the shower. It becomes a heat exchanger as warm water passes around the copper cold line.

I've taken a couple drinking fountain water coolers apart to reclaim the copper and they have a heat exchanger on the drain to cool the incoming water. Just a tightly coiled and soldered 3/8 line around the drain for about 10 to 12 inches. I would imagine if it's worth doing that for a brief few seconds of cold water going down the drain it must be pretty effective.

Today's end will mark 3 full days of DHW metering.. we're looking at about 75 gallons per day so far. Although, It's not a fair representation yet.

That would translate into about $16 per month (136 pounds) for coal OR a whopping $78 per month for electric.

Based on running the Axe 10 months that'd be 1360 pounds

I’ve seen those reclaimers, you can buy them, I think not sending any hot water into your septic all winter could cause problems.. having one would deff cool down the water goin out.

So far the average is looking like 70 gallons of DHW usage per day.

Based on 70 gallons of DHW per day...

$73.12 per month with electric
$15.27 per month with coal

If I run the Axe for 9 months..
658.08 potential cost of electric
137.43 cost of coal for DHW
520.65 saved

That money saved will buy me 2.2 tons of coal

Fun fact...

1.5 gallons per minute × 8.251 pounds per gallon × 75 degree raise × 60 minutes

Running the shower taxes the boiler about 55,700 BTUs per hour which is almost half its capable output.

Making DHW in real time can be quite a load. Now that you have that big well pump try two showers at once.

Rob R. wrote: ↑

Sat. Dec. 11, 2021 9:55 pm

Making DHW in real time can be quite a load. Now that you have that big well pump try two showers at once.

I suppose showering with a friend doesn't qualify as two showers at once?

Lightning wrote: ↑

Sun. Dec. 12, 2021 10:23 am

I suppose showering with a friend doesn't qualify as two showers at once?

That has other advantages, but doesn't change the boiler load.

We have a high flow fixture on our bathtub. When filling the tub it really makes the boiler run a long time.

Thanks Lee and RobR,

Some of us have been making claims that DHW loads have always been greater than our heating loads. For some that has been hard to wrap their heads around.

McGiever wrote: ↑

Sun. Dec. 12, 2021 11:36 am

Some of us have been making claims that DHW loads have always been greater than our heating loads.

True.. my heating load could only be that high on the absolute coldest days of winter. Its difficult for some to see it that way since I might use at most 1 ton of coal per season to heat water and an additional 6.5 tons to heat the house and out building. But in order for the boiler to be able to keep up with both, taking showers and heating the house and outbuilding on the coldest days, it needs to be able to output a minimum of 110,000 BTUs per hour or else it will fall behind.

Here is where a variable speed controller would come in handy. It'd be nice to slow the combustion fan down in the shoulder months and summer for DHW only.

Mac, can you recommend a controller that would be suitable?

McGiever wrote: ↑

Sun. Dec. 12, 2021 11:36 am

Thanks Lee and RobR,

Some of us have been making claims that DHW loads have always been greater than our heating loads. For some that has been hard to wrap their heads around.

That is almost always the case in new construction. In older houses, it depends.

When my house was really drafty, and we could only use one shower at a time due to the old galvanized piping, the heat load was higher. Now that we have tightened up the house, added a third bathroom, and repiped the entire house so that multiple fixtures can be used at one time... The domestic hot water load can be much higher than the heating load. A good example is when we get home after a day of hockey games. One boy gets in the shower, one gets in the bathtub, and the washing machine gets started. When that happens my EFM runs for an hour without stopping.

McGiever wrote: ↑

Sun. Dec. 12, 2021 11:36 am

Thanks Lee and RobR,

Some of us have been making claims that DHW loads have always been greater than our heating loads. For some that has been hard to wrap their heads around.

Rob R. wrote: ↑

Wed. Nov. 24, 2021 11:36 am

Keep in mind that once you are out of the heating season, the efficiency of the boiler making DHW drops like a rock.

I.e. it takes 15-20 lbs per day to keep the boiler up to temperature, and a couple pounds to make DHW. If running the boiler allows you to avoid running a basement dehumidifier, that makes the numbers look better.

Those are really helpful pieces of info for me, I thought I was doing something wrong because over the summer my usage was near 20 lbs/day. I was thinking mine just wasn't as efficient as others. Although until I get my house insulated my heat load will certainly be the most...finally got it tuned that it can circulate and the boiler can keep up! Although I still have some unburnt in there...

Lightning wrote: ↑

Sun. Dec. 12, 2021 11:52 am

Here is where a variable speed controller would come in handy. It'd be nice to slow the combustion fan down in the shoulder months and summer for DHW only.

Come on man... just do what Don does and swap pulleys winter pulleys, summer pulleys . But... on the other hand, if you had an outdoor reset controller and varied the fan and feed speed to the outdoor temp

Lightning wrote: ↑

Sun. Dec. 12, 2021 11:52 am

Mac, can you recommend a controller that would be suitable?

Lee, I have all the extra parts here for you to get all set up. It takes a special single phase VFD coupled to a 3 phase pulley motor.

Let me get things sorted and I’ll pm you.