Pressurized System with Storage, How to Heat DHW?

[velvetfoot]

How do you heat dhw with a pressurized system with storage? I have an indirect water heater now with my oil boiler. All it is is another zone. Is that the way it is with a wood boiler? I saw a post recently that made me think of this: would recovery be real slow when storage temp is low?

 

[huffdawg]

Check my public display link at the bottom of my sig. The schematic shows 2 DHW. tanks. And yes recovery is slower the lower the delta t. sometimes the pump could stay on for quite some time.

 

[Boil&Toil]

Certainly could be depending on the size of the heat exchanger - you'll get very different rates with 180F heating loop water and 120F heating loop water. If it's oversized now, it may work fine; if it's "just right" for oil boiler temps, it will probably be too small when the temperature is low.

Now, if you are using an "insulate it yourself" pressurized storage tank, wrapping the tank with a couple hundred feet of PEX before you insulate it and running your cold water through that PEX before it hits the Amtrol (or whatever brand of indirect you use) could make a big difference in recovery time. Sidearm exchangers also seem to be common here. Adding another indirect in series is another option to raise the rate.

 

[velvetfoot]

Check my public display link at the bottom of my sig. The schematic shows 2 DHW. tanks. And yes recovery is slower the lower the delta t. sometimes the pump could stay on for quite some time.

That link doesn't work for me. This one, (broken link removed) , showed two indirect tanks.

 

[velvetfoot]

Certainly could be depending on the size of the heat exchanger - you'll get very different rates with 180F heating loop water and 120F heating loop water. If it's oversized now, it may work fine; if it's "just right" for oil boiler temps, it will probably be too small when the temperature is low.

Now, if you are using an "insulate it yourself" pressurized storage tank, wrapping the tank with a couple hundred feet of PEX before you insulate it and running your cold water through that PEX before it hits the Amtrol (or whatever brand of indirect you use) could make a big difference in recovery time. Sidearm exchangers also seem to be common here. Adding another indirect in series is another option to raise the rate.

it's an Amtrol Boilermate. 30 gallons, I think. I might try it with the lower temp. of reset rather than the 180F setup I have now, to see how it reacts. Maybe they even have something on their website.

The coil around the tank is very interesting. Indeed, why not do it when the tank is bare and not yet insulated.

I also have an electric water heater. Might be an idea to get that in the mix as well, instead of running the oil boiler when a certain storage temperature is reached where it becomes impractial (maybe uneconomic, with the electric pumps running forever), run the electric water heater.

 

[timberr]

I use a programable thermostat in the sereis with the wiring for my DHW aquastat. I have a 60 gal indirect and the use of DHW is pretty predicable in our house. The programable thermo was cheeper then a digital timer. It took some tweaking on the programing but know it works well, no long cycles trying to warm DHW to 140* with 140* storage.

 

[velvetfoot]

I use a programable thermostat in the sereis with the wiring for my DHW aquastat. I have a 60 gal indirect and the use of DHW is pretty predicable in our house. The programable thermo was cheeper then a digital timer. It took some tweaking on the programing but know it works well, no long cycles trying to warm DHW to 140* with 140* storage.

So, how does that work then? You heat the DHW tank only when you're pretty certain there's a fire going, like in the evening?

 

[maple1]

it's an Amtrol Boilermate. 30 gallons, I think. I might try it with the lower temp. of reset rather than the 180F setup I have now, to see how it reacts. Maybe they even have something on their website.

The coil around the tank is very interesting. Indeed, why not do it when the tank is bare and not yet insulated.

I also have an electric water heater. Might be an idea to get that in the mix as well, instead of running the oil boiler when a certain storage temperature is reached where it becomes impractial (maybe uneconomic, with the electric pumps running forever), run the electric water heater.

I have a couple hundred feet of pex stuffed into my storage enclosure, just as the above post mentions. It supplies all of the hot water needed for say a quick shower, and more - but after a long run of laundry, the water coming out of it is pretty cool.

After the pex comes out of the storage enclosure, it goes though a sidearm exchanger (DHW side is convection - but if hot water is running there is some forced flow through it from that), then into my 80 gallon electric hot water tank. This winter I have been depleting my storage before firing, typically down to 130/115. We have all kinds of hot water - having the 80 gallons in reserve helps with that in prolonged DHW draw.

Now, if you want to heat DHW from storage in the off-heating season, that won't work quite so well - sidearms aren't as efficient as say a plate exchanger. Last summer, once the top of my storage got below 140 or so, it wasn't having much effect on my DHW. So, I have a new 20 plate FPHX to put in (I will just put it in series with the sidearm & leave the sidearm where it is), and a B&G Ecocirc circulator to pump the DHW side as well. I was still able to streatch 4 days between burns doing what I was doing, but I should have been able to do more. I also will add heat traps when I do that, and once everything else is in place & done, will add a layer of extra insulation to my electric DHW tank.

I have no experience with an indirect - but with only 30 gallons in reserve, it might not work out so good in the off-season. I would think it would do OK with the regular firings of heating season.

 

[henfruit]

What you could add with your 1000 gallons of storage is a screw in coil in tank to make your domestic hot.

 

[velvetfoot]

maple1:

I'm thinking about not running the boiler during the summer. In fact, I've already received a directive concerning that subject.

The coils around the storage would help even more since we have cold well water.

Our cheap electric water heater is 40 gallons.

 

[velvetfoot]

What you could add with your 1000 gallons of storage is a screw in coil in tank to make your domestic hot.

I'd like to find out more about that.

 

[peakbagger]

I have a boiler mate that runs off a separate zone. I dont use a lot of hot water and the boilermate is heavily insulated so I only charge it up when I am running the wood boiler. I started wiring it so that it would run off storage like any other zone but decided not to as I have solar hot water as a backup. It lines up that in winter weather I am running the boiler daily and there is plenty of hot water to charge up the boilermate daily, once in shoulder season the SHW system is active as a preheater and it acts to stretch out my hot water in the boiler mate. Sometime around April 1st , the SHW is putting out enough hot water that the boiler mate goes off line and I run off the SHW tank which has a set of electric elements that I have never hooked up. Worse case is shut off the wood boiler and my oil boiler runs as the final backup. Its my excuse to exercise the boiler. If I didnt have SHW, I would probably buy a heat pump hot water heater and hook it up to the boiler mate. (As if I didnt need another complication on the system !).

 

[velvetfoot]

So, if you run out of dhw in the wintertime, and you're not firing your wood boiler, does the oil boiler come on, or do you have to start a fire?

 

[henfruit]

I'd like to find out more about that.

It is a hot water coil that get screwed into a 4 inch port. Your cold water is plumbed into one side and hot will come out the other. The out let water will have to be run through a mixing valve to temper it down to a useable temp.You could use this in the winter months and go back to the electric in the off months.

 

[henfruit]

So, if you run out of dhw in the wintertime, and you're not firing your wood boiler, does the oil boiler come on, or do you have to start a fire?

The way the system is set up with storage is, as long as the water temp is above what you have it set at with the aquastat the oil can not run. When the temp drops below the # the oil will come on. You will then decide to start a fire to heat up the tank or burn oil?

 

[velvetfoot]

I was referring to peakbagger's post.

Is there enough surface area to provide enough flow for a normal shower, and how low can the storage temps go and still get a normal shower?

 

[peakbagger]

The boilermate has three controls on the zone wiring, The original control is the temp switch in the boilermate that determines if it is above setpoint, one is hooked to the SHW tank and locks out the zone when the SHW storage is above 140F, the second is a standard heating setback thermostat used as a timer. Normally I have the setback thermostat in the off position, but when it is on it will only let the boilermate run during the morning and evening when the wood boiler is running. The oil boiler controls and zones are always on but the boiler will not fire if the storage temp is above 140 deg F. If the storage is less than 140, the oil boiler fires and goes into standard hot start mode where its always warm and if I turn the hot water thermostat on the Boilermate will heat up with hot water. If the storage is above 140 I have turn off the wood boiler system and then the oil boiler runs.

Having multiple heating sources and options does require some understanding of the controls. I used relay logic on the wood boiler and storage that integrates the oil boiler and even that logic is complex. With a PLC , automated valves, and few more temperature sensors I could make the system easier to operate but have avoided PLCs as my long term experience is that the software needed to program them gets obsolete and a few years down the road and finding the software to modify the logic is a PITA and sometimes expensive if even possible.

 

[velvetfoot]

Thanks. I'm gonna have to read this a few times.

From a wider view, it seems like there are various solutions.

 

[arngnick]

I tried to heat water with a plate exchanger but it was not very good. I know some people are happy with it but I found the best solution was to use an indirect tank. You will not get good heat out of any solution if you have a low delta T. Since you hae the indirect go with it.

 

[maple1]

I tried to heat water with a plate exchanger but it was not very good. I know some people are happy with it but I found the best solution was to use an indirect tank. You will not get good heat out of any solution if you have a low delta T. Since you hae the indirect go with it.

What was your exchanger & setup? What wasn't good about it?

 

[arngnick]

What was your exchanger & setup? What wasn't good about it?

I had a loop and a circulator on the hot water side and a loop on the storage side with a circulator mated with a 40 plate exchanger. In theory there should have been nothing wrong with it but it took forever to heat water. I am not sure if there was to much restriction at the exchanger or the flow was not right. thermostat placement could have been an issue on the hot waer tank also. I tried several different variations but I was never happy. I have an indirect tank now and it i working great.

 

[nwomatt]

I have the same set up with a sidearm. Not much success either.

 

[maple1]

I have a sidearm that works great in heating season, together with our bottom-fed 80 gallon electric hot water heater. The boiler side of it is zoned with a ZV, and pumped via the Alpha load circ when the ZV opens. The DHW side just circulates by convection - but some of the cold incoming flow also goes through that when the hot water is running. I have the ZV wired thru an ordinary electric hot water heater stat that I have tie wrapped onto (and also insulated around) the bottom tank fitting right up against the tank - that is also where the domestic side of the sidearm gets fed from. All kinds of hot water, for us anyway - the stat closes the ZV when the temp at the bottom element is around 120, by that time the temp at the top element as around 140. But when trying to heat from storage in the non-heating season is where my setup falls short. I've got a 20 plate HX to add on above the sidearm, and an Ecocirc to plumb into the domestic side, after this heating season is over. Hoping for the best with that.