demand on defrost - worth it?

[wakko]

so i'm looking to replace an old heat pump.

Is the demand on defrost something that I need to get? or is the timed defrost adequate?

[second opinion]

Think of it this way, do you stop and get gas every hour that you are driving or do you stop when you need to?

[wakko]

When I need to. So would systems like the byrant evolution 16 not be worth considering?

[tigerdunes]

Electronic Demand Defrost feature eliminates nuisance,unnecessary, and expensive defrost calls.

It should be standard on all HP condensers. Unfortunately timed defrost is so cheap a feature.

IMO

[BaldLoonie]

My HP has a timer set to 90 minutes. I am so fed up with unnecessary defrosts that I'm going to replace that board with the board from a step up model of the same brand just to get demand.

SO, that was a great way of describing timed defrost.

[tedkidd]

Electronic Demand Defrost feature eliminates nuisance,unnecessary, and expensive defrost calls.

It should be standard on all HP condensers. Unfortunately timed defrost is so cheap a feature.

IMO

And since the majority of buyers can't differentiate on anything but price, gotta strip features to compete.


Wakko, I believe all high end carrier products only go to defrost if they need to.

I also believe that if you'll regret it if you don't run the numbers on the new Greenspeed, particularly if you are already decided on carrier/bryant. Heating efficiency is nearly 50% better than the 19 seer Infinity unit.

[amd]

My HP has a timer set to 90 minutes. I am so fed up with unnecessary defrosts that I'm going to replace that board with the board from a step up model of the same brand just to get demand.

SO, that was a great way of describing timed defrost.

Don't unnecessary defrost cycles last a very short time because there's no ice to melt?

What's the efficiency penalty of timed defrost?

[BaldLoonie]

Depends on the weather. In 30° ambient with the big coil, it can take 3-4 minutes to get it up to 70 or whatever it shuts off at. That's witch a clean, dry coil. Now, on a unit that runs when it is 0° out, it could take the whole 10-12 minute allowed cycle to warm the coil if there is any breeze at all. 10 minutes in cooling out of an hour or 90 minute run time is a lot!

The best I've seen out of Carrier is a variable timer. It looks at past defrosts and adjusts the frequency based on that. Sure beats a fixed timer but will still defrost every 90 minutes max if the coil is below freezing. Which is any time the outdoor ambient is much below 40.

[rundawg]

Sure beats a fixed timer but will still defrost every 90 minutes max if the coil is below freezing. Which is any time the outdoor ambient is much below 40.

It will do a 120 min interval if the last defrost cycle was < 3 min.

[JWB]

Very interesting topic. I would love to read my indepth about this. I would install a better board on my two heatpumps tomorrow.

[Tommy1010]

Wakko, I believe all high end carrier products only go to defrost if they need to

all trane condensers high end and low end use demand defrost on there heat pumps

[wakko]

so in climates where winter averages are in the 40s demand defrost isn't that essential? what i'm taking from everyone is timed defrost is inefficient and a hassle but not a nuissance as it won't take 10 mins to defrost in warmer climates?

[Tommy1010]

so in climates where winter averages are in the 40s demand defrost isn't that essential? what i'm taking from everyone is timed defrost is inefficient and a hassle but not a nuissance as it won't take 10 mins to defrost in warmer climates?

timed defrost does not take any longer to defrost at all

what it will do is defrost more often than needed compared to demand

[tedkidd]

what it will do is defrost more often than needed compared to demand

...Wasting energy unnecessarily by running in Air Conditioning mode. Possibly a fair amount of energy.

Also creating a fair amount of unnecessary wear and tear. Imagine driving on the highway cross country and having to pull over every 45 minutes to drive a quarter mile in reverse.

[carene 7]

Let's not forget the electric heat that cycles with each defrost cycle.Fondly remembering the old days of GE with their pressure switch defrost,the ultimate in simplicity and 100% demand operated.

[lynn comstock]

Climate matters somewhat. In Yuma, AZ we often go years at a time without a defrost cycle. 970 Heating Degree Days and dry to boot. Nevertheless demand defrost is the ideal solution. Timed is rather dumb.