Posted by schooner on October 29, 2005, 11:58 am
I was more just looking to get a ballpark idea just to gauge whether out
collector is working at a respectable level or not. We just did a first
test run yesterday with the unit outside taking in approx 50F and output of
120-130F. This was just test to make sure the thing worked at all :-)
Posted by Morris Dovey on October 29, 2005, 3:51 pm
firstname.lastname@example.org (in email@example.com)
| A temp gain seems fairly meaningless by itself. Lower temps might
| indicate better performance, with less heat loss to the outdoors.
| How would you measure airflow?
It pretty much is. Lower temps on the *same* passive collector
probably would not indicate better performance. How? Using the
handy-dandy flowmeter the guys here on a.s.t suggested. Did that (but
not yesterday) and then hung some yarn at the top of the discharge
opening to tell me what I want to know without needing to chase down
fresh batteries and spending more time than I want massaging numbers.
After keeping an eye on this thing for a couple of years, I can fairly
accurately predict the yarn deviation from vertical by glancing at the
thermometer - which takes only a second or two. How often do you
actually measure flow through your shop panel?
DeSoto, Iowa USA
Posted by David L. Jones on October 30, 2005, 5:24 am
Outlet temperature means nothing in itself without knowing the airflow
No point pumping out 70degC air if your airflow rate is 1m^3/hour.
Much better to have 30degC air and 100m^3/hour.
It is all about how much total energy you are pumping into the room,
not what temperature you are pumping in.
If you must know some typical figures though, my 1.6m^2 collector can
typically get 40degC outlet temperature with close to 100m^3/hour
airflow rate. And the collector is by no means optimally angled, so the
actual collector area is less than 1.6m^2.
Without any airflow at all a collector plate can easily get >100degC
Posted by nicksanspam on October 30, 2005, 8:28 am
How do you measure the airflow?
Posted by David L. Jones on October 30, 2005, 8:35 pm
An anemometer on the outlet. You have to be careful to take a number of
readings over the entire outlet and average the result to get the most
CFM based on your duct size.
Hot wire anemometers are the most accurate at low speeds (the air-con
installers use these), but vane type ones are much cheaper.
Overall it's hard to get a very accurate measurement, as there is
significant error involved. But at least it gives you a typical figure
that you can then use to calcuate:
- A power output graph for your collector (like this one
- how quickly you can heat a room of a given size by a given
- The total efficiency of the collector.