DHW

Paul S_3

800,000 btu steam boiler being replaced. 18 unit apartment building with 22 full bathrooms and each unit has a kitchen with dishwasher. lifestyle for the occupants is nothing crazy.normal showers in morning and at night(shower heads 2.5gpm) about 15 min showers. while running dishwashers at end of the day. about 3 occupants per unit. about 50 residents in total. I'm trying to find a reliable and efficient way to provide hot water for them. which would you guys prefer? using a tankless coil with new steam boiler as a heat exchanger and run a indirect tank/s (plus would be no need for venting).... stand alone high recovery water heater ? or an external heat exchanger running off a condensate loop? I really do not want to use any tankless water heaters I have seen may break down at the worst time....I came up with 2GPM per shower multiplied by 15 minutes which equals 660 gallons first hour rating does this seem about right? this is for a peak load in morning

Firecontrol933

What did they have before for hot water?

Paul S_3

steam boiler oil fired with tankless coil....

SWEI

Have you run through the full sizing calc? http://www.statewaterheatersizing.com/ApplicationData/Apartment.aspx should take about three minutes...

Paul S_3

I tried using the lochnivar calc....its saying 93 gallon storage at 450 k btus...to cover peak hours...I think some info is incorrect....I will try the state sizing application now...

Paul S_3

state application came up with 300 USGPH for med peak demand and 538 for high peak demand..... you guys recommend indirects with heat exchanger or standalone water heaters?

SWEI

Within a certain range, you can always trade storage for firing rate.

The sizing app will give you a defensible first hour demand number (based on ASHRAE numbers.) You and the owner can decide together to make adjustments, which can help keep you out of hot water (pun intended.)

Paul S_3

any advice on which setup I should go for?using a tankless coil with new steam boiler as a heat exchanger and run indirect tank/s (plus would be no need for venting).... stand alone high recovery water heater ? or an external heat exchanger running off a condensate loop to indirect tanks?

gennady

DHW coils with storage tanks. Run tanks at around 160F, mixing valve after tanks.

Paul S_3

Gennady do you mean use the DHW coil in boiler and just add storage tanks to it with a bronze circ pump in between? no indirect tanks? Like the pic below?

Paul S_3

Hatt I'm giving the customer a few options with certain recommendations.....if I use the steam boiler with an indirect would you use a heat exchanger?

Paul S_3

weil mclain 880 about 1million input...steam MBH 654,000....what about tankless coils with external storage tank?

SWEI

Agree on the indirect.

You could add a summer boiler sized for the lower rise, which would also provide a winter boost during an extended run of design conditions.

If you go with tankless coils and plain storage tanks, you might be able to pair that with tankless water heaters sized for summer, but I'm a bit less clear on the value prop.

JUGHNE

Are you oversizing the steam boiler to accommodate both space heating and DHW? So when the DHW storage tank is satisfied in the middle of the night would the steamer cycle on pressure because of oversizing?

I have had tenants and it is bad if heat is not working, but if no DHW also that really upsets them and the phone would ring a lot with 18 units x 3 people. All this is dependent upon one heat source.

Also the best efficiency the steamer can do is mid 80%.
HW boiler or condensing water heater could reach 95% (they claim). DHW is probably a large portion of the NG bill.

That is a lot of boiler to heat the basement all summer long.
IMO.

SWEI

Let me reverse the logic above. Size a condensing boiler or tanklesses for summer, then use the steamer to boost as needed in winter. Keeps the efficiency high for all but the peaks and you still have redundancy.

JUGHNE

That would give some redundancy for DHW also. But would the steamer be still be oversized for heating the building? Short cycling more than it needs to? It seem logical to get the steam boiler as small as possible, it still will be too big for 80-90% of the heating season.

The separate water heater would modulate to the size needed for the usage......unlike the steamer.

Paul S_3

no I'm not oversizing boiler...edr is about 2685 sq ft...boiler puts out 2725 sq ft. using a PF gas burner.

Paul S_3

872k includes the pickup...654k is the 2725 multiplied by 240. Each tankless coil can handle 6.5 GPM continuous draw I can add more if I need....never sized a tankless coil....a separate boiler for DHW is a long shot I do not have so much room in boiler room.

Rich_49

Just how much room is Available Paul ? Height ?

Dhw coils , boilers and indirects , boilers and indirects and help from the steamer , who's on first and what's on second .

Maybe this is a fit for your project if you have room .
http://www.htproducts.com/phoenixplusspecifications.html

Paul S_3

height is about 10 feet...room is roughly 15 X 12'

JUGHNE

So for my own education; the pick up factor of 33% about 290-300 MBTUH is what would heat the water. So on design day at 5-6 AM, coldest time, the steam piping would be heated up already and the pick up BTU's would be extra and used for the morning showering. Is this the logic??

Paul S_3

yes....in Dans book it says never go over the pick-up factor for DHW and/or condensate loop

JUGHNE

Thank you Paul S. So in the evening for the DHW, we would probably not be at the design temp and rads do not need to heat completely across? Thanks again.

Paul S_3

Thanks Hatt.... just for my knowledge the continuous draw for 1 hr is 6.5 GPM multiplied by 60 gives you the 390 GPH...along with the continuous draw rating of the 119 gallon storage tank gave you the 480GPH...

gennady

Paul S said:

Gennady do you mean use the DHW coil in boiler and just add storage tanks to it with a bronze circ pump in between? no indirect tanks? Like the pic below?

Yes. Just add mixing valve on the tank outlet. tanks size app 200 gallons, or 2x100 USgal tanks, piped reverse return. pipe boiler to the bottom of the tanks, hot water outlet to mixing valve on the top.
set tanks temperature to 160.
add sensor/aquastat to the tank outlet to cut off pump at 190.

Paul S_3

Why would i want to cut the pump at 190F? Wouldn't the pump cut out once the tank is satisfied at 160F?

gennady

Paul S said:

Why would i want to cut the pump at 190F? Wouldn't the pump cut out once the tank is satisfied at 160F?

when there is no usage of hot water, temperature difference between bottom and top of the tank is about 40F. Relief valve on the top of the tank trips at 210F.
When boiler is producing steam, heating water temperature shoots over 210F, tank top overheating can happen because aquastat is usually installed in lower part of the tank. mixing valve or bypass should be installed before the pump, but i usually don't see it installed, so second control helps.

Paul S_3

Continous draw rating @ 6.5 GPM with 200F boiler water (40F TO 140F)..... I can add another 6.5 or I can upsize to a 8 GPM coil

gennady

Paul S said:

Continous draw rating @ 6.5 GPM with 200F boiler water (40F TO 140F)..... I can add another 6.5 or I can upsize to a 8 GPM coil

When heating is off, you cannot go over 160-180F boiler aquastat setting on DHW call.
Boiler will start making steam.
better to have oversized coils.

Paul S_3

ok...thank you Gennady

SWEI

Hatterasguy said:

Once you add a pair of them and flow them at 6.5 GPM, you're looking at 780GPH continuous @140°F which would be more than sufficient to accommodate the building WITHOUT a storage tank.

As long as you keep the boiler hot 24/7/365, of course. That's a fair bit of jacket and stack losses. There's also the possibility of temp suckout during short-term peaks. What happens when five showers overlap for two minutes?

ChrisJ

What happens if someone like me wants a nice 40 minute shower and is using a 2.5 GPM head?

Can't say it doesn't happen because I do it whenever my arthritis is bad. Transforms me from Herman Munster into a normal person. Well..........as normal as possible.

SWEI

ChrisJ said:

What happens if someone like me wants a nice 40 minute shower and is using a 2.5 GPM head?

The mixing valve throttles the flow through the coil and delivers your 40 minute shower.

Paul S_3

Supply house gave me a quote for (2) 15 GPM coils with (2) 119 tanks....seems like overkill.....i was thinking maybe (1) 119 tank....price for extra tank and piping miniscule in this job....its the room im worried about. Customer is renovating basement and part of boiler room wall and 1st floor maybe i can convince him to extend the wall he has room....(these are professional people i do not want to undersize....everyone goes to work in morning)

SWEI

Are you still considering an alternate heat source for summer? How hard is the water? A couple of 199k condensing tankless in parallel feeding that 119 storage tank might be able to handle it, depending on the groundwater temps.

Paul S_3

I can ....but space is an issue.....i can fit another boiler with 2 tanks its just going to be tight

SWEI

I'm thinking single tank. If the water is relatively soft, ganged 199 tankless heaters would feed a plain storage tank. A boiler an an indirect would probably be a better option if they have hard water. Check your chloride levels, too.

Either option could be wall-hung, which should save some space.

jonny88

Ergomax reverse indirect with storage tank?Not sure how it would work of a steamer.

SWEI

Slightly different flavor of indirect. You'd run the separate DHW boiler through the tank and pipe the steamer tankless coil in series with the Ergomax coils. I suppose you could run the boiler tankless to the tank water.

I'm not sure what value the added mass brings there with that size steamer and all the mass it already has onboard.

jonny88

I was thinking on the lines of feeding storage tank from indirect.Great thread Paul and this is a good tutorial.Understand what you are getting at Swei,thanks.Good luck with it Paul.

SWEI

You'd need some kind of bypass valving to keep the coil in the steamer from absorbing heat when the steamer was turned off. I think a manual seasonal suhtdown/bypass of the steamer would do it. In the event of a failure in the other heat source, there would be a service call involved, but it wouldn't take more than a few minutes to get the DHW back online. Automatic fail-over would be more expensive, and would still have to wait for the steamer to come up to temp.

Interesting design and controls challenge, I agree.