Sustained delivery of 180F flow

[mapratt]

Gentlemen (and any ladies present!) -

My pasteurizer fabricator is asking for:
- 20-25 gallons per minute of
- 180-190F water flowing through a brazed-plate heat exchanger,
- which will drop the water temperature by about 20F for the return,
- for ~45 minutes
- and the system should be designed / built to operate at 15psi or less

I'd also like to use the system for in-floor heat, and for domestic hot water.

Can a stratified thermal store do this? or might I need two thermal stores - one very hot and one less so - tied together somehow?

 

[Frozen Canuck]

Folks are going to need more info on the other two loads you mention to give you an idea of what size boiler you will need. You have detailed the pasturizer load nicely if you could add info on the other two loads as well then the helpful folks here can help you narrow it down based on load and any other info you would care to include, such as where the boiler would be located, distance from boiler to other loads if the boiler is not in the residence or barn I am assuming. Keep asking plenty of folks here willing to help.

 

[Frozen Canuck]

Oh BTW the short answer is yes but as always the devil is in the details.

 

[mapratt]

Thanks, FC -

The house is about 1000 square feet, currently uninsulated. There is a good fireplace insert, but the heat from that doesn't get to all the corners, and of course to get heat the fire has to be constantly burning. I'd like to put in under-floor radiant heat, then insulation under that. Climate is south-central coastal Oregon - definitely not as chilly as central Canada.

It's a 2-bedroom house on a farm, but the DHW system will also serve the dairy. It's a sheep dairy, so the wash-down requirements are low (think washing dishes and mopping the floor in a 9x12 room) (it's a small operation), but there will be a clean-in-place system that will consume ~60 gallons/day.

The milking parlor, milk house, and cheese-make operation are going into the house's garage, which is separated from the house by a breezeway. The barn where the animals sleep is a few hundred feet away and down a hill, and is not supplied with hot water.

I'd like to use an indoor boiler, and will put in a thermal store. The boiler will be located in a to-be-built addition to the house that is about 20 feet from the pasteurizer. I can co-locate my hot water heater. I'll insulate my lines.

The clean-in-place system is maybe 5 feet further away than the pasteurizer. The first rinse needs to be with warm water (100-130F), then very hot water for the wash cycle (165F or higher). This water is "consumed" - not circulated through the boiler system. I do have an electric unit to boost the DHW temp to 165 for the wash cycle, but of course I'd like to save the electricity for this if I can use a heat exchanger here too.

Thanks again, and I hope you aren't too buried in snow!

 

[ewdudley]

Gentlemen (and any ladies present!) -

My pasteurizer fabricator is asking for:
- 20-25 gallons per minute of
- 180-190F water flowing through a brazed-plate heat exchanger,
- which will drop the water temperature by about 20F for the return,
- for ~45 minutes
- and the system should be designed / built to operate at 15psi or less

I'd also like to use the system for in-floor heat, and for domestic hot water.

Can a stratified thermal store do this? or might I need two thermal stores - one very hot and one less so - tied together somehow?

20 gpm * 20 degF deltaT * 500 = 200000 btu_per_hour, 200000 btu_per_hour * 0.75 hour = 150000 btu.

Pasteurization at 170 degF, raise milk from 90 degF to 170 degF, 80 degF deltaT, assuming pasteurization during miliking. (Or alternatively, assume milk is cooled to 39 degF and heated to 170 degF and scale everything by 1.6 in the end.)

150000 btu / 80 degF deltaT = 1875 lb milk.

Of course system cannot transfer 100% of hot water energy to the milk, so assume pipes and system delivering hot water are losing 50%. I would hope not, but let's just be pessimistic. So we've go enough heat to pasteurize 900 lb milk.

1000 lb milk per sheep per year, 900 lb milk per day (per milking?), works out your fabricator is designing a system to handle a minimum of 300-350 sheep, is that about right?

--ewd

 

[Hunderliggur]

Gentlemen (and any ladies present!) -

My pasteurizer fabricator is asking for:
- 20-25 gallons per minute of
- 180-190F water flowing through a brazed-plate heat exchanger,
- which will drop the water temperature by about 20F for the return,
- for ~45 minutes
- and the system should be designed / built to operate at 15psi or less

I'd also like to use the system for in-floor heat, and for domestic hot water.

Can a stratified thermal store do this? or might I need two thermal stores - one very hot and one less so - tied together somehow?

25GPM * 45 minutes = 1125 gallons of 180-190F water. You will be left with 1125 gallons of 160F-170F water (plenty to heat the house and do the wash up). Looks like you have a batch need of a lot of very hot water once a day (we have dairy gots, much easier to milk). So, I think you would want a control system (nofossil can probably customize one) that would give priority to getting the pasturization done once a day (morning I assume), then the rest of the loads. If you have the space, you could have two storage systems, 1000G for the pasturizer and some more for the house and always keep the pasturizer tanks HOT. However, you will need to look at the costs and payback period fo this arrangement - what does it cost you to produce 200KBTU of hot water now? With propane, it would cost me about $10.00. You are doing this 365 days a year (I assume) so that would be $3650 saved in propane costs. Having a year round energy need like this makes the boiler payback much quicker.

We use raw goats milk ;-)

 

[heaterman]

Gentlemen (and any ladies present!) -

My pasteurizer fabricator is asking for:
- 20-25 gallons per minute of
- 180-190F water flowing through a brazed-plate heat exchanger,
- which will drop the water temperature by about 20F for the return,
- for ~45 minutes
- and the system should be designed / built to operate at 15psi or less

I'd also like to use the system for in-floor heat, and for domestic hot water.

Can a stratified thermal store do this? or might I need two thermal stores - one very hot and one less so - tied together somehow?

Two options are available to you. Install enough storage to supply the roughly 1250 gallons of 190* water or install enough boiler "horsepower" to drive that HX.
BTW, regarding the heat exchanger and its use, is it going to have water on one side and milk on the other? If so, I think that dairy requirements will dictate that it be a plate and frame type heat exchanger rather than brazed plate. The reason is that a brazed plate cannot be taken apart, cleaned and inspected. Maybe a better question; Is the heating load you mention used for processing the milk or cleaning the equipment?

Is the pasteurization process one pass or is the milk recirculated multiple times allowing it to reach 170*?

25gpm @ a 20* drop is a transfer rate of 500,000 but/hour net capacity. You'll need to design your piping sizes accordingly which porbably means at least 1-1/4" or more likely 1-1/2" pipe in the boiler/storage side. If you squeeze the flow down the system will not be able to deliver the heat needed.

I'm rambling because I don't understand the process you need the hot water for. .........

 

[Hunderliggur]

My suggestion for a "batch" system (with 1000+ gallons of target use temp water) was to be sure that here was sufficient process water at the start of the operation. I would hate to be 1/2 way through the pasturization process and have a firebox issue (bridging, etc.) cause a problem. The load is not excessive and could probably be done with a single tank. Fairly easy to do the math if you want the tank to be dual use and determine the pre-procesing charging time. For the potential payback, a dedicated process storage tank may be in order and improve the KISS factor.

 

[mapratt]

You gentlemen are amazing. It's going to take some time for me to reply properly, and I need to get to my day job, but let me take a stab at it here...

Mr. Dudley - I suspect the requirements are rather dramatically oversized, but I also realize I still need to provide more information to help answer a couple of questions above... I should draw the system out, which I can't do right now (gotta get to work!), so I'll try it in words...

The pasteurizer will be a used stainless-steel jacketed steam kettle from a commercial kitchen. We will pass water of the appropriate temperature through the jacket to heat and cool the water, for pasteurization and for making cheese. The water for the pasteurizer will be in a closed loop. We will be pasteurizing the old gentle way, at 145F for 30 minutes.

Another loop will go from the boiler system to the above loop of water, heating the p. water via the brazed plate exchanger. Thus there is water on both sides of that transaction, not water and milk, so I think that answers Heaterman's helpful concern. A third loop will go from a chiller and back, using something like the brazed plate heat exchanger to affect the water in the p. loop. I don't have the knowledge to draw out whatever mixing valves, etc., will be involved.

I'm expecting to get up to 80 ewes max, but do plan at some point to have a few (a very few) Guernseys involved, and possibly a small herd of goats. We are currently planning to milk once a day (mornings) and leave the lambs with their moms during the day. I may go from udder to vat sometimes, but also have the facility to chill and save milk, to make a larger batch to work with. This is really a very small farmstead operation.

Hunderligger - all I can do with raw milk is make cheese aged 60 days or more, and we want the flexibility to offer other products. I wish I could just use raw milk. Really. For my own consumption, it'll be raw.

 

[mapratt]

I think I have one question still puzzling me - does the 15psi limitation mean I can't use pressurized storage? or is 15psi ok for pressurized?

I started to draw something, but there's too much I don't know yet. So, to simplify some of my rambling above:

For the pasteurizer there will be, I think, three loops of water:
- one loop that serves the pasteurizer itself. It's a closed loop.
- one loop from the boiler to the pasteurizer loop, for heat. Closed loop to boiler. Can be pressurized only up to 15psi, else we get into more complication, certifications, etc.
- one loop from a unit holding water and antifreeze, held at ~21F, to cool things down. Closed loop again, not pressurized.

The pasteurizer will be a used stainless-steel jacketed steam kettle from a commercial kitchen. We will be pasteurizing the old gentle way, at 145F for 30 minutes.

I grok installing enough storage to be sure I have capacity at the start of pasteurization, to be sure it doesn't fail part-way through. And I understand I could do 1 or 2 storage tanks, doing a cost-benefit analysis of the second tank for domestic use.

I'm almost confident enough to have a coherent conversation with someone I can buy equipment from ;-). I'll keep you folks posted on what happens. Would appreciate thoughts on 15psi.

Thanks again!

 

[Frozen Canuck]

The only mention I see of 15 psi is from yourself, so I will assume that the 15 psi is either a limitation of the pasturizer (safe operating pressure limit), or a restriction placed by code officials (max psi ) they will allow a system to be operated at without trained personel to operate it, ( 4th class power engineer here) not sure about Oregon.

To answer your question 15 psi is fine for storage, pressures higher than that simply allow you to raise the boiling point of water even more than the 15 psi will.

 

[mapratt]

Thanks, Canuck - yes, it's a limitation imposed by regulators. Possibly operating personnel, definitely a host of added requirements for inspections and certifications.

The things you learn from google - so, it could get to ~250F at 15 psi, and that's the traditional cut-off for low-pressure versus high-pressure systems. Ok, I think I'm basically ok here - thanks everyone! Thanks, Canuck!