My hydronic heating system has been up and running at least partially for over a year and the completed system has been operating for several months.
I ended my previous post at the point where I had decided to use an automotive radiator for the delivery heat exchanger and my buddy Dick Paterson was good enough to give me one that he had had custom built for one of the iterations of his rally mini “Betty”. This was duly installed and I’m glad to report that the system operates exactly as designed and, after a few minor teething issues is proving to be very reliable.
After operating the system for most of last winter, during the finishing of the house interior, I finally got to install the tubing under the main floor, which is “engineered” hardwood over plywood, during the later part of this summer.
I had originally intended to attach the pex tubing to the underside of the subflooring with plastic staples which are sold for this purpose but after thinking about it for quite some time decided that I would be better off with heat transfer plates. These thin aluminium plates are about 24″ long and 6″ wide and have a groove pressed into them wherein the pex tubing is located. The plate is nailed or stapled to the underside of the subfloor between the floor joists which serves to hold the pex tubing as well as fulfilling its task as a transfer plate. After installation the entire cavity between the joists is filled with insulation which prevents the heat from traveling down and heating the ceiling of the room below.
TRANSFER PLATES – “My logic”
When I was originally researching these systems I came across a number of discussions on the benefits of transfer plates. I originally sided with the “nays” who maintained that putting an aluminium plate in the cavity under the floor, but above the insulation, would make no difference to the amount of heat to which the floor was exposed and therefore would make no difference to the amount of heat that the system could deliver for a given water temperature.
After long deliberation however I decided that the plates could indeed make a difference because a large portion of the outer surface area of the pex tubing would actually be in contact with the aluminium plates. Where this contact occurred I figure that the aluminium will quickly conduct heat away from the outer surface of the pex tubing thus creating a larger temperature differential across the plastic of the pex tubing. As the flow of heat is proportional to the temperature differential there should be a faster transfer of heat.
Whether right or wrong I opted to use the transfer plates and the system delivers a very even and comfortable heat to the hardwood floor surface.
For the entire house including the garage there is about 3000 sq. ft of heated floor which used about 2800 feet of pex tubing.
I run both the input (boiler) and delivery closed systems at 10 p.s.i. This is mainly to ensure that any leakage can be detected and to aid in eliminating any air bubbles from the systems.
Elimination of air from systems of this type is very important because the impeller type pumps used to circulate the water will not operate if air gets into them. To ensure that all the air is out of the closed circuits in my system I have installed two Maid-O-Mist bleeders one on each system; in fact the boiler came equipped with one when I bought it.
These quaint little devices have been around for decades and are simple, inexpensive and very reliable.
The major teething problem was caused by my failure to realize that the surfaces of a new concrete tank, when first filled with water will leach lime into the water causing it to become seriously alkaline!! Copper radiators, and oddly the solder used in their construction, does not like this alkalinity and rapidly dissolves !!!!
This initially became apparent when the input side of the system started to loose water resulting in an ongoing loss of pressure in that circuit. After checking everywhere for leakage I decided that the leak must be inside the storage tank so I cooled the system down and drained the tank to check. Sure enough my Nissan radiator was leaking like a sieve. I had a new heavier core custom radiator built by York Spring and Radiator and installed in late in September. I refilled the system and just to be sure purchased a pH meter to check the tank water. It would seem that the initial fill and drain removed all the lime as the tank water has remained absolutely neutral (pH 7) since this repair and there have been no additional leakage problems, in fact I have not had to add water to either of the closed systems for several months.
Of course the original intent of this system was to save heating costs by using low (off peak) electricity to heat the house. Unfortunately this has not, as yet, come to pass. Hydro One, our local supply utility has been very slow to implement the TOU (Time Of Use) metering system that they were required to install and are probably not going to actually activate the Smart Meters until the final deadline date of summer 2011. In addition to this the provincial government, in its infinite wisdom, has decided to increase the price of “off peak” power by 20% thus eliminating a large portion of the incentive to switch to TOU pricing. Read about that here.
A further complication is that I was unaware of the large difference between Rural and Urban “delivery” charges. My original calculations, used to compare the relative costs of fuel oil, propane and electric heat, priced our “all in” rate at $0.112 per kWh. With the changes now the actual rate, for the volume we use will be nearer $00.1918 / kWh before HST!!!
When the TOU actually comes on line this will decrease to to around $0.17/ kWh but that is is still a 50% increase over the rates that my original inquiries revealed. The nett result of all this is that using electricity to heat the cottage, even with the TOU pricing will be more expensive than oil or propane.
Fortunately, although the advantages of the storage system would be lost, the system can quite easily be converted to use a different fuel as the boiler is the only “electricity specific” component of the system.
In my next post I will explain the control systems I have installed for the heating system.