Posts Tagged ‘Hydronic Heating’

New Heating System, One Year Later

Thursday, October 29th, 2009

Well, it’s that time of the year again.  The weather is cooling off and we’ll have to begin the heating season once again.  The performance of the wood boiler has been very good, although with last winter being colder than normal we ended up using about 6 cords of wood between October 2008 and June 2009.  Operationally we’ve made very few tweaks to the control system software, and the variable speed circulator that controls the storage tank loop has proven to be magic.  PID tuning of its control loop was pretty easy, and if I wasn’t doing more monitoring and research, the control system could be greatly simplified, reducing it to something any HVAC technician or homeowner could maintain. Using  just thermostats and a couple relays, and one of those little PID controller 1/4 DIN modules from Automation Direct would be enough.  There have been no issues with reliability, everything has worked as designed.  Also, when I took a water sample from the boiler drain at the end of the heating season, it came out crystal clear, thanks to maintaining a system fluid pH of about 8.5.

I can’t emphasize enough the importance of maintaining the proper pH level of the water in the system, since this is responsible for ensuring long system life and minimizing any corrosion problems.  Many hydronic systems are severely neglected regarding this.  A friend of mine who installs geothermal systems reports that since he started raising the pH of the water in the ground loops and heating loops of the systems he installs this has virtually eliminated problems with rust and corrosion.

-Jeff

Determining Rate of Heat Transfer in Hydronic Systems

Friday, January 2nd, 2009

A friend of mine recently asked me how I made all the heat transfer calculations on the new FOM heating system. He’s also in the HVAC business but does forced air and geothermal mostly, and has not dealt much with hydronic heating systems. We’ve both seen a number of “hack jobs” where outdoor wood boilers have been lashed up to existing forced air or new radiant systems. I asked one homeowner who was having some problems with his new radiant system to show me the heat loss and heat flow calculations for the job. The ensuing blank stare told me this was not going to be a fun visit. With all the computer programs out there these days that simply plug and chug and give you numbers close enough to work with, there’s no excuse for not doing things properly. But I digress, we are supposed to be talking about heat transfer!

Heat transfer calculations in hydronic systems are dead easy, so there’s no excuse for not running the numbers. In the USA we still use BTU for our units for heat. Recall that 1 BTU is equal to the amount of heat that causes a temperature rise of 1oF of 1 pound of water. Let’s say we have something like a geothermal system that uses a ground loop. A fluid, usually water or water mixed with glycol to prevent freezing, is circulated through the ground loop outside and a heat exchanger inside, either transferring heat from the refrigerant circuit (summer cooling) or transferring heat from the ground to the refrigerant circuit (winter heating).

  1. A geothermal system is operating at steady state in cooling mode. If the flow rate in the ground loop is equal to 10 gallons per minute, the temperature of the water entering the loop from the heat exchanger is 110oF and the water returning from the ground loop is 90oF, what is the amount of heat, in BTU per hour, that is being conducted into the ground?

Answer:

heat transfer(BTU) = ΔT * Flow rate(gpm) * 8.3 * 60, where ΔT is the temperature drop around the ground loop in degrees F from input to output.

We simply multiply ΔT times the flow rate times weight of 1 gallon of water times 60 minutes. We have to multiply by 60 to rationalize our units since flow is in gpm but we want to know the number of BTU’s per hour. Since 8.3 * 60 = 498 it’s common to write the heat transfer equation simply as ΔT times flow times 500, to make it easier to do ‘rule of thumb’ calculations in one’s head. So the answer to our question is then:

20 * 10 * 500 = 100,000 BTU per hour.

So remember, it’s simply delta T times flow times 500. Not so hard, is it?

Phase 1 energy upgrade complete

Tuesday, November 11th, 2008

FOM Systems, Inc. is happy to announce that the first phase of our energy upgrade is complete.  Our wood gassification boiler is up and running, and working like a charm!  We had a late Indian summer this year which lasted until all the pipework and post installation operations were completed, with time to spare.  So far we seem to be using about the same amount of wood daily as we had previously when we were simply firing a wood stove, but now the entire house is warm, not just the downstairs, plus we have a virtually unlimited supply of domestic hot water.  We are still experimenting with the boiler firing rate, and yes, it is possible to put too much wood in at one time, as well as too little it seems.

So, how does one move a 1700 pound piece of machinery up one and down 16 steps through a narrow stairway and into the basement?  Very carefully!  Step one is to gather the right equipment.  Russ brought his forklift with an extension beam on it.

Using a forklift with extendable beam

Using a forklift with extendable beam

At the distance we needed the moment arm was calculated to be able to lift about 3100 pounds so we decided this was the best option to use to get the boiler downstairs.

Ready to start the long descent

Ready to start the long descent

Once we were all done measuring things and got the boiler unbolted from its pallet, everything was fairly straightforward, until we got to the bottom of the stairwell…

Can we get it through the door???

Can we get it through the door???

With a bit of head scratching, adjusting the beam, and a change of the clevis securing the lifting ring of the boiler to the beam, we were able to get the boiler through the door and set it flat on the basement floor, with essentially no room to spare up and down. There was plenty of side clearance to get through the door.

Boiler just barely fits through the door, with the beam attached.

Boiler just barely fits through the door, with the beam attached.

Once we were able to get the boiler sitting on the floor inside the door, moving it around inside the basement was simple using a couple of skates and a Johnson bar. But anyway, that was the end of the most exciting part of the whole affair. We still had a lot of plumbing ahead to connect the boiler to the new storage tank and the existing radiant system.