Add a tank to my indirect to increase capacity?

wrooper

I have a flat plate heat exchanger indirect using a 40 gal electric [no power] tank. I want to expand the capacity of my system without increasing my boiler temps [for efficiency]. I use a direct vent,cold start, oil fired, Laars Max with a through wall flue [flue length is approx 7']

The boiler control drops to 140 F during the summer with a Hydrostat control and the DHW tank is set at 130F which seems to work well. We rarely run two showers/ hot water uses but when we do the water temp available drops.

We are also nearing the point where we will sell the house and if a large family moves in I could imagine they will run out of hot water too often for comfort.

What I picture doing is piping the second tank in series with the original tank. I am having difficulty picturing the correct piping plan? Is it as simple as routing the output of the original tank into the second tank and the output of the second tank to the house piping? I can picture a problem of standby loss [while on vacation?] dropping the house supply temp?

Or maybe I should be piping the flat plate to exit one tank and enter the other? If I do that? which tank gets the cold supply ?

There is likely other options but I have just started considering the plan

STEVEusaPA

Are you sure your current set up won't keep up with domestic demand? How does it do in the winter with heat & domestic?
You could make the piping and the flat plate heat exchanger bigger for more capacity. Flow rates are important too.
You can also put the domestic on priority.
EK has many setups with just a flat plate heat exchanger and a small tank, and reported (by many here) endless domestic hot water.

wrooper

Thanks for the reply. We used to have a System 2000 in our last house and I designed this system as a copy. The old system used 180 F water temps and indeed had nearly unlimited hot water. I assume the difference is the lower boiler temps I am trying to use/the Hydrostat "calculates" [why couldn't they allow an adjustable differential?]

I actually switch from DHW priority depending on weather but of course in summer/shoulder seasons [we get good passive solar] it doesn't matter

HVACNUT

If you have the Hydrostat 3250 Plus and you're only using the priority switch on the zone board, that's not good enough. The Hydrostat doesn't know the difference between a heat or hot water demand.

Set the Hi limit to 180°
Turn the Lo limit off.
You need to run a wire from ZR on the Hydrostat and splice it in parallel with the hot for the water heater circulator.
Keep the zone board switch on priority.
Set the switch in the Hydrostat to "I".
Remove the jumper in the Hydrostat if it's there. Just to the left of the switch.

Also use the Economy settings. Economy will be overridden on a DHW demand.

Zman

Your boiler is not designed to condense, condensing will damage it. 140 is really low the boiler is probably condensing for most of, if not all of the DHW cycle. Running it that low is likely not saving you any energy because the boiler is cycling. How does the system keep up if you set the boiler to 160?

Big Ed_4

You can sister in a second tank in parrelle . In series is used to make hotter water like in a commerical aplication , Parrelle for more volume .

Use the same hight tank for the second tank .How to pipe depends on the arrangements of the taps of the tank . If cold and hot run off the top . Two tees would be needed . To equalize the draw of hot water for supply , pipe one tee on the inlet or cold on one tank and pipe the second tee on the outlet or Hot on the other .

To help equalize the temperature between the two tanks... Pipe an equalizer pipe between the two drain valves . No second pump needed , The temperature with equalize with gravity .

If the return from the heat exchanger is piped to the bottom of the tank , pipe it now to the center of the equalizer .

Valves and purge valves can be added to back flush and clean heat exchanger ...

HVACNUT

> @Zman said:
> Your boiler is not designed to condense, condensing will damage it. 140 is really low the boiler is probably condensing for most of, if not all of the DHW cycle. Running it that low is likely not saving you any energy because the boiler is cycling. How does the system keep up if you set the boiler to 160?

I didn't write it in the post. The OP should have the manual. The 3250 Plus has condensate protection even if the Lo limit is off. He needs to set that feature.

Zman

Trying to get a heat exchanger to produce 130 out with only 140 in is not going to work well unless the the HX is huge. Forget the 2nd tank and turn the temp up.

wrooper

Thanks for all the replies

u/HVACNUT you described a control change but isn't clear what it accomplishes? Your wiring plan will get me 180F for DHW calls only and not affect the other calls use of the Hydrostat demand adjustments to boiler temp?

u/Zman Condensing has not been an issue in 12 years. I'm using the same 7' of thin flexpipe flue [well after I remounted the sidewall vent to tilt out the second winter] and no signs inside the boiler

u/Big Ed_4 thanks, parallel it is, I was confused.

My existing piping

Cold supply enters the tank drain, directly above it the circulator pumps to the HX

The HX ouput goes into the top of the tank [an abbreviated dip tube]

The house hot supply draws off the other top tapping

I looked for a System 2000 DHW piping diagram but couldn't find it. There is a youtube that shows it briefly. My DHW piping copies the System 2000

HVACNUT

Before I bury myself. Is the Hydrostat the 3250 Plus?
If not, what model?

wrooper

HVACNUT Thanks for the reply

Yes, 3250 Plus with a Jan 2016 manufacture date

HVACNUT

Using diagram 5 on page 5, a DHW demand will override the economy settings and run to to the Hi limit setting.

The Hi limit doesn't need to be 180° but I wouldn't go lower than 160°.

Look through the manual for all your options.

A thermostatic mixing valve on the water heater is also a good idea. It will act as a higher capacity tank and kill bacteria. Set tank temperature to minimum 140°, max 160°. Set the mix temperature to 120°.

wrooper

I missed giving some details. We use alternative heat on high demand days [pellet] and have floor radiant [undermount pex with plates]. I use mixing valves to temper the floor heat supply, adjusted at a 150F [approx] boiler temp to limit the floor supply to 110 F [or so, gives a floor temp of 85F]. So to protect the floors my Hi Limit is set at 150 despite the fact that the system won't meet heat loss at that temp.

I am concerned that if I set my high limit to 180 I will overheat my floors? when we aren't home to supplement the heat.

Am I wrong to assume that increasing my DHW volume available at 130 and still keeping my high limit at 150 will save energy/protect my hardwoods?

Zman

The mixing valve should be protecting the hardwoods. There is no way you should need temps to the floor higher than 140ish. The best option for the floors would be a smart mixing valve like the Taco I-Series. That way you can use outdoor reset, talk about saving money.

Does the boiler cycle during a call for hot water or does it run one long cycle?

hot_rod

What size is the boiler, with a .large or multiplie you could possibly produce 3 gpm instantaneously

If the current set up works or can be adjusted to, why bother complicating It?

wrooper

the delta T for my floors is in the 20F range so with 180F supply water the minimum temp I can get with my mixing valve [theoretically assumed, I haven't tried it] is in the 170F range

wrooper

sorry, yes I do get short burns with DHW calls alone. The Fing Hydrostat has a set 10F differential. Not much I can do about it

My heat loss calc said I needed 60k BTU. The smallest [mine] I could find in 2007 was 80k BTU. I have tried to adjust it down but got a dirty burn

Zman

Heat exchangers are all about temp differentials. I bet if you turn the boiler up to 170, it recovers faster and does not cycle.

Zman

wrooper said:

the delta T for my floors is in the 20F range so with 180F supply water the minimum temp I can get with my mixing valve [theoretically assumed, I haven't tried it] is in the 170F range

Sounds like it is time for a new mixing valve. There is no reason for that.

wrooper

"there is no reason for that" ?

In my mind the "reason" is the return water [theoretically] from a 180 boiler is 160 [delta T of 20]. How can I get a mixing valve to supply temps lower than 170?

In any case, we are off point IMO. I would like to keep my boiler temps lower for efficiencies sake

Zman

Radiant systems usually have either thermostatic or smart mixing valves. Maybe yours is fixed? With the correct valve, you can run the floor at any temp you like regardless of the boiler temp.
The difference in efficiency between running the boiler at 140 vs 160 is minimal. You will probably make hot water 3x faster by turning the boiler up. It also will be able to run without cycling and for a shorter amount of time (more efficient).
I think you are inadvertently creating a "need" for another tank by running the boiler at the incorrect temp. The efficiency difference (if there is any) will never pay for the additional tank, pump, and piping.
It costs you nothing to turn the temp up and observe, I think the results will surprise you.

hot_rod

You have an 80K input boiler now? So you have about a 68K actual usable output. Not enough to do continuous hw at any useable rate. So then the next question is how much DHW and how quickly do you need it?

If you use a tub, a typical 5' tub holds 80 gallons, so you need enough storage to cover that load over a 15- 20 minute fill. then that 64K needs to recover the depleted tank.

If you pull the tank down to say 105° and need to recover back to 130 you need to look at the performance of the plate HX.

You can download free HX sizers online and plug in the data. Size of the HX, flow rate and temperatures. Then you can predict how long it will take that 68K boiler to recover the tank to 130F.

A typical gas fired water heater would be 40K, minus the derate factor, maybe 30- 35K actual burner to water..

If you add more storage, yes you have more dump capacity, but also longer recovery.

Cheapest route if you do not want to change boiler settings might be to series an electric tank. Double your capacity and add some additional horsepower. A 4500W element gets you another 15,000 BTU/hr input.

Really you need to define the target first.

Zman

There are 2 components is a DHW calculation. How fast can you heat the water and how much storage do you have. An instantaneous heater needs a lot of BTU's because it has no buffer for high demand periods. A typical electric water heater doesn't have very much output so needs more storage. The approach you are taking is throttling your output which in turn is requiring more storage.
If you have large jacuzzi tubs to fill, you may need the storage either way. My point is, why add storage when you have plenty of BTU's at your disposal?
Another approach, especially if turning the boiler up solves the problem, would be to increase the size of the HX so that the boiler can run at 100% at the lower water temps.

wrooper

My mixing valves are TACO Model 5000, basic thermostatic valves. They mix my return water with the supply water . I am having difficulty understanding how they can "provide any temp water" independent of supply temps [and return temps at Delta T of 20F] ?

Yes, I am trying to increase dump capacity . Recovery time [while related] hasn't been an issue. I suspect [as everyone has said and I acknowledged] that if I ran my boiler at 180 F my existing system would provide more hot water. There is at least one fellow [on this forum] that has emphasized repeatedly that the key to efficiency is the ability to run lower temps. I happen to believe him [I forget his name, I think he wrote one of the bibles of hydronics] I don't think he was referring only to condensing, he talks a lot about increasing emitters.


I can buy another tank for under $400. I suspect there is a way to pipe the second tank to my first to increase my dump capacity to 80 gals. I suppose I could experiment but hoped there would be advice available

hot_rod

Increasing boiler temperature will not increase your dump capacity, it increases recovery.

Increasing the storage temperature will provide more dump capacity.

3 way thermostatic valves blend some cold with some hot to supply the required mix temperature. So if you store the tank at 140F, which is the minimum temperature for bacteria protection, then some cold mixes with that 140 to get the 105 or whatever you desire at the faucet. Set the valve to the temperature you want, typically 115- 120F, and the valve maintains that.

wrooper

I can't increase the tank temp [and add mixing valve to increase capacity] without increasing my boiler temp. I am familiar how DHW mixing valves work.

The mixing valves I am talking about are tempering my floor heat and unrelated to the DHW except to the extent that mixing supply/return water has a limited capacity to temper the floor heat. eg If I increase my boiler temp to provide volume through recovery improvements I can't temper the floor heat low enough

Zman

You seem set on purchasing and installing an additional tank. To answer your question we would need to know how the water is presently being circulated through the tank and HX. You will probably pipe the in parallel/reverse return.

Please see the attached graphs and see the

Zman

This one is a little more generic

HVACNUT

@wrooper
There's confusion here but I don't have the smarts to explain theory.

Say the boiler is set to 180° Hi, 160° Lo.
Say the radiant zone delivers 114° SWT.

If I increase my limits to 200°- 180°, I can still achieve the 114° mix for the radiant. The mixing valve knows, or properly functioning,
is supposed to know, and adjusts itself accordingly.

Hope that helps.

wrooper

ZMan I am happy to discuss theory some other time. It seems your graphs confirm what I believe, the lower temp you can safely/effectively run your boiler the more efficient it is. I am happy to turn my boiler up to 180 to increase/speed recovery. What I don't understand is how I get 125F through my mixing valve when the two inputs are 180 and 160.

AS I described in my earlier post. My DHW is the same piping as a System 2000.

The cold supply enters through the drain tap. A tee off the drain tap goes to my circulator which feeds the HX. One of the confusing parts [see below] is this setup quickly forces cold replacement water through the HX as the house pressure overcomes the circulator.

The output of the HX goes into a top tap of the tank,there is an abbreviated dip tube in that tap.

The house supply is the other top tap.

The piping change I am considering is to route the HX output to a top tap in the the added tank. The other top tap will be routed to the initial tank, where the HX output used to be.

I was curious whether I needed to move the cold supply to the added tank and now I believe it is necessary. Otherwise the added tank would warm from the circulator but not get moved to the house supply.

With the cold supply entering the second tank a house supply use would allow the second tank's water to be forced into the first tank while being refilled by the cold supply. I would get 40 gallons with little cold supply mixing. The second 40 gallons [approx] would start the circulator which would begin warming the second tank again.

Jeez writing this out is confusing me more... but I guess as long as the first tank's input is at least beginning to be warmed I would get more than 40 if not 80 gals of 135 F water.

I guess I might move the circulator too? but then only the second tank will reach temperature and the call for heat will never stop...

HVACNUT How do I get 114 F mix from 180 and 160 inputs? I would posit that it is impossible. A boiler mixing valve isn't magic, it just mixes supply and return water

hot_rod

Maybe some drawings of your piping would clear this up,
If it is piped properly The 3 way blends return from the radiant, generally below 80 degrees with the hot from the boiler supply, to get, say 114F or whatever you set for

Really no difference from how it functions on a water heater.

With a properly sized heat exchanger you should be able to get 120 tank temperature from 130 boiler temperature

My solar HX gets to within 5 degrees It does require a large size HX to get “close aporoch”

wrooper

what is the delta T that provides 80F returns? The difference with a water heater is your mix water is 50F



This is not a condensing system

Zman

wrooper said:

This is not a condensing system

Exactly, that is why you will not see the savings. Look at the graphs.

If you post pictures and drawings we can help you get your mixing correct and tell you how to pipe the second tank. Otherwise there really is no "helping" that can happen.

"never try to teach a pig to sing, it wastes your time and annoys the pig..."

wrooper

"look at the graph"

correct it is a curve and efficiency increases as temps decrease even if you can't get to a condensing system's temps safely [more importantly effectively, an older system generally lacks the emitters to use the lowest temps and still meet demand]

I couldn't find a diagram of the System 2000 DHW piping but this video shows it pretty clearly. You may have to pause it to see it clearly. at 13 seconds it shows the cold going in at the drain with the circulator directly above it leading to the HX mounted above the boiler shell. The output of the HX goes to the top tap in the tank

https://www.youtube.com/watch?v=KmBygRJL1KA

Big Ed_4

What you have is an Aqua booster ,A form of an indirect , a indirect with an external heat exchanger .I am assuming a check valve is added to force the in coming cold water though the heat exchanger first . The idea is to heat up the in coming cold water , to supply hot water longer and also flush the heat exchanger . The draw to piping this way is the hot water pressure would drop with the extra resistance though the heat exchanger ..
When I pipe it that way , I would set it up to back flush the heat exchanger which would clean the heat exchanger better on a on a hot water draw ... A check valve is needed to direct the water though a heat exchanger eather which way .

If pressure is important , , remove the check valve and add valves to back wash and clean the heat exchanger when needed . It's up to what is wanted ...

Hot water needs are so different in every household .. Recovery or storage . Hot water would be the biggest load in most house holds ... In spectrom, Take Aunt Maggie in on home with a shower a day , and then there's Gorge with three daughters in the other ... Gorge good luck , He would need a bank of tanks and heated with a 500k boiler and he may still have complaints .. The more you can produce the longer they would be in there .

Using the cold tap of the tank which has a dip tube for the supply of the heat exchanger is a way to mix the water for more even temperature . To prevent stacking , Very hot on top and very cold on the bottom ..

wrooper

Big Ed_4

I sent you a separate message as you were the only one who actually attempted to answer my original question about piping changes

My system doesn't force all incoming water through the HX [pipe sizing precludes it] but the circulator does draw off the incoming cold supply. The dip tube off the HX supply is cut shorter by a foot or so. Not sure why, it was part of the System 2000 install instructions.

If you have seen a System 2000 DHW setup? mine is the same.

szwedj

@zman I meant to pm @wrooper with that message, sorry if screwed that up some how.

Joe

wrooper

Thanks szwedj !

Unfortunately your post came after I had added the tank/repiped. I see your method would do a better job of balancing the temperature of the tanks and perhaps force my boiler to fire sooner/get a jump on recovery/reduce some piping restriction. Should I have found that in my 12 year old System 2000 manual? I still need to know how to wire two different tank thermostats to a single circulator?

Big Ed_4 also mentioned a balance pipe and I still may do something along those lines

Results?

I ran my original setup as a baseline and drawing hot alone in my slop sink I was able to run for 10 minutes before the water cooled to approx 104 F [based on what felt like hot tub water] from approx 130F to start. Note that is without any flow restriction , flowing around 3.5 gal/min to a bucket.

With my second tank piped[as described above] I was able to run for 23 minutes before the water dropped to 104 F

As an aside, the only temp gauge I had was a cheap non-contact thermometer and I learned before the second test that to get an accurate reading on a glossy surface [chrome faucet in this case but same on copper pipe] you can put a wrap of electrical tape on the pipe.

Disconcertingly the boiler didn't fire/circulator start for 18 minutes? I think the series? piping didn't allow the thermostat to register the temp loss until both tanks were nearing "empty" [my circulator is still running off the initial tank thermostat which is the "second " tank away from the cold supply.] This is a limitation in that that the circulator doesn't start/boiler doesn't fire until late in the game which I imagine will delay my recovery if I ever need it.

I would call it a qualified success?

HVACNUT

Internally the System 2000 tank is different.