OT - Geothermal Heat issue...?

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Kenneth wrote:

I don't know enough details of your setup or the structure to be able to run the numbers. The main objection I'm seeing is that it's likely to cause the resistance elements in the heat pump to kick in but you say that you don't have any, but there might be something else unique to your situation.
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We are running multiple schools on ground source heat pumps. Each building has a single loop with individual Trane heat pumps running in each classroom tapped onto that loop. There is NO auxiliary heat. There are NO heat strips. Our Energy Czar believes in night set backs and holding temperatures at minimums until someone gripes. The systems are computerized to central control and the units can only be changed from the central location other than a small allowance at the thermostats.
Each building, or even portions of buildings, have different thermal mass/draft and air leakage issues/poor glazing/etc that each requires its own start up time. Some take 2 hours, some almost 4 hours if they have been allowed to get too far out of design or conditions are extreme. The water loop is circulated full time through the well field, but the compressors at each heat pump function by thermostat. The buildings have become so much easier to control that we continue to install these systems as money permits. The buildings are so much more stable that we tend to ignore old fashioned insulation/draft/weatherstrip conditions - perhaps we will get back to them as energy costs continue to spiral.
Our HVAC technicians would prefer just letting the systems run full time and maintain a steady temperature, especially when equipment is new just to run it through its paces while under warranty. The Energy Czar tends to win. I will try to remember to ask tomorrow about the whys.
Each well field happens to have hit multiple water tables, so each field is way under capacity as they are originally designed on the assumption of no significant water zones and rely on ground contact through the custom gel only. We have two sites without well fields that run the loop through a cooling tower (no chiller) and small redundant boilers with plate frame exchangers. These were the first 2 sites when too many folks were afraid of the ground source. Who knows on a 20 to 50 year cycle, but right now groundsource is far and away the most efficient, cleanest, lowest maintenance system out there. We're not walking, we're running!
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A 'medium-insulated' school building full of people doesn't need _any_ additional heat source until the outside temperature gets below about -20F.
Look up how much heat an 'at rest' human body gives off, and multiply by the 25-30 bodies preset in the average classroom.
Getting the heat _out_ of the building is the issue.
At 'above zero' temperatures, it's _common_ to be venting hot air outside and pulling in cold outside air for 'make-up'.
Not infrequently, the chillers will be running, in addition.
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Robert, as you said, bodies and lights make a huge load on a building. Our Energy Czar (EC) lets the buildings get cold enough that they typically require a morning warm up before the occupant load takes over. We have one 2 pipe school that requires a full conversion to either heat or cool that can be quite troublesome on those moderate days. We turn all chillers off and dump the cooling towers as we head into the freezing months. The buildings can usually be tempered by outside air. The geothermal schools eliminate this problem and allow partial usage of buildings for special events and summer school type needs.
I did ask about the setback issues. We had one series of heat pumps whose open/close valves did not have stops installed. These machines have a sensor that says if the water is too cold it prevents the unit from running rather than make ice - this issue was rectified by installing stops that never allow the valves to completely close which keeps the water circulating back to the loop. We now install all systems to run the well field pumps continuously as we have one that turns off the circulating pumps if there is no demand anywhere on the system which can allow some of the loop to reach that same "don't run" temperature. Believe it or not, the pumps have shut down several times because the building is that stable. As Robert says, lights and people can keep a large building quite warm or too warm when the rest of us need heat. We do continue to have a problem with people wanting cooling on warm afternoons turning the thermostat down to the bottom at 55: the computer limits the units so the 55 never happens, but the units also don't come up on morning warm-up, though the rooms seem to recover quickly if the rest of the building is satisfied. He swears emphatically that no matter what system is used, intense run time in the mornings uses less energy than the start/stop cycle of leaving the system at temperature around the clock. They have put in-line monitors with recording capability on units set up each way on highly similar usage, run them for a week, then reversed the study for another week on the same units. Setback with a substantial run time to recover uses less energy than maintaining the temperature during non critical times. The setback needs to be able to protect critical needs as in not freezing water lines or baking cookies in the attic.
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Robert Bonomi wrote:
... snip

From EDEE 101 (or Physics 112), we were told that the average human body is equivalent to 100 watt light bulb as far as heat output. Depending upon age, kids in a school would most likely be considerably less.

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You haven't seen my 11 year-old granddaughter - 250 Watt is more like it.
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Han
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Depending on activity level, you can _triple_ (or somewhat more) the base number, which is in the 100-140 watt range.
A 250 watt kid is -not- all that extreme! <grin>
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snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote in

area, which would make skinny kids radiate more (proportionally) than chunky ones ...
<grin>
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Han
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While you might think so, reality is somewhat counter-intuitive. :) Total heat output is relatively -independant- of surface area. Less skin just means more output per unit area.
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Han wrote:

You know, I know exactly what you are saying -- our son has been like that also.
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That's a bit on the low side -- about right for sleeping. 'resting' is more in the 110-120 range. Circa 125 is frequently used for estimating purposes.
Call it 12,000 BTU/hr per room, plus another few thousand for the lighting.
Scale up by a factor of 4, for equivalent footage to a medium house, and you've got the equivalent of an 80% efficient 150,000 BTU/hr furnace running at a _50%_ duty cycle.

Surprisingly small differences. lower elementary ages are about 75-80% of adult.

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dpb wrote:

If the structure had no thermal mass then that would be the case. But it does have thermal mass and changing the temperature of that thermal mass requires the addition or removal of heat.
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J. Clarke wrote:

But the time integral is still less...
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dpb wrote:

Or not as the case may be.
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"Robatoy" wrote

I had an old volvo that had a thermostat that would die on a regular basis. So I just ran without the thermostat. The problem with this particular configuration is that it took over twenty minutes for it to heat up. And until it heated up, you had no heat, defrosters and the engine did not run well.
But volvo engineers had a unique solution. They had a window shade type device located in front of the radiator. You pulled a chain under the dash to pull the shade up over the radiator and it heated up quick! This model also had a baby bottle warmer under the dash as well.
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That is the first I ever heard of that.
The higher the flow rate the higher the Reynolds number and therefor the higher the convective heat-transfer coefficient. You may get less heat transferred per gram of water flowing through the radiator, but not in inverse proportion to the rate at which grams of water flow through. IOW you might get only 75% of the heat loss per gram of water but will have twice as many grams of water flowing through.
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Fred the Red Shirt wrote:

Yes, it's simply wrong in general. If one didn't get additional cooling capacity when the thermostat opened as compared to when it is closed, there would be insufficient cooling capacity to prevent overheating at almost any operating condition.
Whatever "caveats" were suggested to counteract that would have to be extreme, indeed...
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If he's talking bout a new engine them maybe removing the radiator could confuse the computer and really screw things up--but since normal operation is for the thermostat to open when the water gets hot--how COULD it overheat by leaving ti open? Once it gets hot, it would open anyways.
Sound's like an old wive's) mechanic's tale.
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Er, I meant removing the 'thermostat'.
There is little doubt that removing the radiator will cause the engine to overheat...
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The fellow you are talking to may not be able to tell you! One point to consider is you can "stress" the ground by pulling a bunch of heat out of it at one time. If you leave an area colder, then bump it up 5-10 degrees the heat pump will run longer than normal and pull an abnormal amount of heat from the ground. Once the ground gets too cold, the equipment does not as efficiently also. Same with air conditioning, but then you are putting heat into the ground.Generally with heat pumps they are slower to heat up the home than say gas or electric, so the equipment runs longer to get to the occupied temps. I am with your heating contractor, leave the temperature constant, unless you have an area of the home you can close off and leave cold for many days. I would not bother to set back the temperature once or twice a day like you might with electric or gas heat. If you want to save money, wear a sweater, and turn the temps down a couple degrees. Greg
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