Calculating a difficult load.

Harvey Ramer

I'm calculating a heatload on a milking parlor. It will have radiant floor as the first stage of heat and high intensity infrared heaters as the second stage. It gets constant ventilation, which i can calculate, but it also has 2 11'x11' openings to the outside, that only have vinyl strip curtains hanging across them. And they get used all the time by the cows entering and exiting. Anyone have any good ideas on how to calculate that?

Thanks!

JUGHNE

Other than keeping things from freezing, are you going for the comfort of the workers or the cows?

Harvey Ramer

I'm going for a 50° to 55° ambient temp.

hot_rod

Harvey Ramer said:

I'm calculating a heatload on a milking parlor. It will have radiant floor as the first stage of heat and high intensity infrared heaters as the second stage. It gets constant ventilation, which i can calculate, but it also has 2 11'x11' openings to the outside, that only have vinyl strip curtains hanging across them. And they get used all the time by the cows entering and exiting. Anyone have any good ideas on how to calculate that?

Thanks!

Those vinyl strip type curtains? Do the vinyl curtain manufacturers list any R value? Of course with animals moving in and out, it is really just an opening, part wind block?

Harvey Ramer

Yes, they are the vinyl strips. I found no reference to any r value. It won't be much. Infiltration is the part I'm really trying to calculate. One manufacturer claims it blocks 65% of the wind. Since the openings are not facing the prevailing wind direction, and are somewhat sheltered, I used 3mph wind @ a 50° TD and calculated the load as though the openings were completely open. That comes to 1,6465,68BTU/H per opening. Deduct 65% and I have 576,298BTU/H per opening.
Thats the best I have for now.

Jamie Hall

And it's probably about as close as you are going to get! Those curtains do surprisingly well, but they're certainly not perfect. However -- you might look into air curtains as well. There's a tradeoff on the energy for the fans and the the energy saved, but it might be worth a look.

JUGHNE

Is there any time that the cow doors are closed with a solid door?
Or is it a continuous milking schedule?
I have been around only the old family farm milking parlors with 2 milking's a day. Parlor shut up tight as possible between these times. The main desire for the farmer was to have warm feet in their working pit. In these small operations the cows gave off almost heat to heat the parlor. This was all small time operation of 30-40 cows. I am sure things have up-scaled.

Harvey Ramer

These openings are for cows to enter and exit the milking robots. The robots are in operation 24hrs a day.

hot_rod

what kind of BTUs does a cow give off, count that into the calc


http://www.motherearthnews.com/Homesteading-and-Livestock/cow-thermal-energy-to-heat-homes-zmaz82ndzgoe

Steve Minnich

Suggest a powered air curtain? Heated?

Steve Minnich

Sorry Jamie - just read your post after I posted.

Harvey Ramer

I don't think an air curtain is an option. It would drive the cows nuts, and it would be a maintenance nightmare given the corrosive environment. Plus we are driving 1100cfm of mechanical ventilation through the building that will exhaust through the doors. Not sure what that would do to the air curtain?

Bob Bona_4

I feel your pain, occasionally running into "unquantifyable" loss. It's almost like a sally port is needed to do this right.

Steve Minnich

Would the infrared thermometer measurement on each side approach work in this app?

Jamie Hall

@Harvey Ramer -- there's your answer. It's not an unquantifiable loss -- you are working with 1100 cfm and most of it is going out through the doors? The specific heat of air is about 0.24 BTU per pound. The density is about 0.23 pounds per cubic foot. Which with a temperature difference comes out to somewhere in the general vicinity of 200,000 BTUh to heat the air which your mechanical ventilation is providing.

I presume that you are using forced draught fans to blow the air into the building? So my thinking would be that you really don't want to count on your radiant floor to provide that -- you want the floor to maintain 50 to 55 for comfort -- so I would be much inclined to figure out how to get that much heat into the air stream just after the fans, with a thermostat to hold it at something reasonable -- like 50. You're not going to get any real positive pressure in the building with those vinyl strip doors, so you might want to add a fudge factor for infiltration...

Harvey Ramer

So you're thinking that with 1100 cfm blowing into the room, the exfiltration through the openings will mitigate the infiltration potential with wind?

According to my calculations, 1100 cfm @ a 50 deg TD requires roughly 60,000 btu's.

JUGHNE

Around here dairy cows didn't go outside in the winter. Too much danger of freezing udder teats and drop in milk and butterfat output.
They had a free stall "loafing shed" where they were fed and watered. That shed was connected directly to the dairy parlor.
It afforded mainly wind protection but was still open for ventilation.
The ceiling had to be insulated or else it would rain inside.
The loafing shed would be a lot warmer than outside. (helping on the Temp diff.)
I would imagine your parlor have that and would you even see any wind?

One thing used around here was a HX that precooled the hot milk with well water, before being dumped into the tank, that then went to the livestock waterers.

Another was a LB White hanging heater, NG or LP, unvented but pretty high CFM blower that was designed to heat a building with exhaust ventilation, typically hog barns. The pressurization aided to vent the building without fans. Just inlet and outlet relief shutters.

The Mother Earth News was always an interesting read. My collection starts with issue 3 and went several years. Some really off the wall ideas were there....some real shoestring budget projects.
However cow power heat should remember the effects of methane and such on copper tubing. A few years and it may leak.
In the old country the family used to live on the 2nd floor above the livestock, mainly for heat......smell? not me, must be the cows.

Jamie Hall

Basically, yes. I made an error in my first calculation, and now I get 55,000 BTUh. Backs of envelopes are very poor places to calculate! I was assuming that that 1100 cfm was coming from forced air fans or blowers? I know it sound a bit bizarre -- everybody "knows" that barns are draughty -- but that doesn't apply to a modern milking parlour. If the rest of that building is tight and the fans can overcome the static pressure from the wind if it is blowing at the doors... the worse case might be the wind blowing at the fans -- assuming you have cross ventilation -- and I might consider dampers on them, which could be partially closed if the wind was wrong.

Then perhaps the floor could be expected to take up the more normal building losses.

Interesting problem. I haven't done any ag. engineering in decades!

EBEBRATT-Ed

1100cfm is not enough air to keep infiltration from coming in the doors.

What's your fuel??

If you have natural or propane what about a direct fired gas fired make up air unit??

If the air is going to come in you need to heat it.

The key is as you said , how much infiltration?. A gas fired mu air is costly to run, but if you can keep the building at a slight positive this could be your MU air source and keep the infiltration out.

If located outside methane and corrosion shouldn't be a problem. I know they are available with non sparking fan wheels.

Maybe call the Cattleman's association for info LOL

Jamie Hall

I agree that the 1100 cfm (only 5 feet per minute) seems too low. Considering that one one horsepower 48 inch fan will give you about 23,000 cfm...

JUGHNE

What Ed said about the Cattlemen's Association holds some merit.
In NE we have certainly more cows than people. Our University strives (hopefully) to be on the cutting edge of cow culture.
I am sure your state also has this interest at heart also.
We would contact our extension office for info concerning livestock ventilation and heating needs. If sheltered in the free stall barn without wind a herd would self heat themselves.

Also out here years ago the equipment supplier was usually on top of barn design. They want the dairy to profit and buy more equipment. FWIW

Where does the heat rejected by the compressors go?

Harvey Ramer

There is a freestall barn attached to the milking parlor. It provides some buffer to the great outdoors but not a heck of a lot. I'm also doing a 3' strip of slab warming outside the cow entrances to the parlor to prevent ice and frozen manure buildup.

According to the people I'm working with who build these dairy setups, these types of parlors are invariably to cold. I have to keep it above freezing and I have to keep the robots warmer than that to keep them functioning properly. That's why the combination of infloor radiant and High Intensity Infrared LP heaters aimed at the robots.

Probably what i'll do is install 4 160,000 BTU/h LP heaters and run the gas line @ 2psi with the capacity to add at least three more if needed.

The heat rejected from the compressors always goes into a water preheat tank. Thats SOP in this area.

tim smith

so there wont be any exhaust in parlor, just makeup air with gravit outlets, ie. door openings? I would think if you have 2 openings for cows that there might still be some infiltration with only 1100 cfm. ???