Quote:
Originally Posted by berniebenz
What is the meaning, defining conditions of the TONage rating of these HXs?
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Great question...
In refrigeration in the USA, the 'refrigerating power' (my term) of a system is referred to in Tons, BTU/hr, Kilo-Watts/hr and Horsepower.
Most frequently, it is referred to in Tons, and the definition of Ton is historical. A Ton is defined as the refrigerating power of one ton of ice over a twenty four hour period. In more modern terms, 1 Ton equals 12,000 BTU/hr. or about 3.822 kilo-Watts/hr. The horsepower rating of refrigeration equipment can be kind of 'squishy' and is not used quite as often. Even though the Ton measure originated with cooling, it is also used as a measure of heat pump output (heating).
So, in the practice of hacking your own system, various factors will dictate the overall size of your system... in particular, how much heat output will be required from your system to supply heat to your house at the same rate that heat is being lost on the coldest winter day. As an example, let's just say that your house required 24,000 BTU/hr on that coldest day... this would equate to 2 Tons.
So, in hacking together your system (or systems), you would choose a compressor that had this capacity, so you would choose a compressor rated at 2 Tons of output. Note that in refrigeration, bigger is not necessarily better. In fact, slightly smaller is best, and be prepared to use some axillary heating to fill in the gap on those extreme days.
Next in your homemade hack-a-thon is the selection of a heat exchanger (often referred to as HX). If you choose a HX that is smaller in capacity than your compressor, your compressor will not be able to realize its full output. If you choose a HX that is equal to your compressor, it will be able to reach full capacity. If you choose a HX that is larger, it can improve efficiency to a certain degree, but you will face the law of diminishing returns, in that a small increase in size will give you some increase in efficiency, but subsequent increases will give you progressively less increases in efficiency.
There have been spirited exchanges in various threads here at EcoRenovator, about whether increases in efficiency will actually occur, and if they do, how much. So far there has been much hot air circulating about this issue, but no rigorous testing that I know of.
It is my opinion that any real increase in efficiency should be vigorously pursued, as I think that the price of energy will be relentlessly climbing.
Another consideration regarding HX selection is where will your heat come from and where is it going to? For instance, I put in a very small hand-dug ground source loop field in my back yard, and I have tested it to be functioning with a very small compressor. Building a bigger system with a bigger compressor and properly sized HXs will not necessarily equate to more heat output, as my loop field is the limiting factor. This leaves me only one solution, which is to reduce my rate of heat loss... AKA: rigorous infiltration remediation, and insulation improvement... I can also reduce the amount of my house that I choose to heat.
Randen built a fairly large loop field to begin with and had enough excess capacity that when he increased his compressor & HXs by 75% (from 2 Ton to 3.5 Ton), he was able to realize that extra output. Last I heard, he is also embarking on adding solar heating to the mix, and additionally improving insulation, as these will reduce the run-time of his heat pump.
I hope this is the information you need...
Best,
-AC