Joe Homeowner needs HP advice...

[RoBoTeq]

There has to be something else going on dash. If the system is putting out the required amount of heat and the air is set for that capacity then the the degree of heat in the system will be the same. The physical size of the coil, whether it is face area or capacity makes no difference in the amount of overall heat being displaced.

Maybe you are running into an issue with higher efficiency systems not running at optimum capacity for a longer period of time. If so, a variable speed blower set to operate at a lower speed during initial operation would resolve the problem.

Either way, it boils down to amount of heat being displaced vs amount of air to carry that heat. With the same amount of heat, regardless of the configuration of the coil, the amount of air is the only other factor affecting leaving air temperature.

[typical homeowner]

For those of you still following this thread...

I kept track of the system cycling today just to see what happens. The house was open last night and cooled to 70 degrees on its own. I closed everything up this morning and set the thermostat to 75 (cooling only of course). The outside temp reached a high of 94, bright sunshine.

Here's a rough chart of how it's run today so far:

First on cycle: 2:58PM, 91 deg outside, run time 10 min, off time 19 min
3:27PM, 92 deg, run time 11 min, then off 13 min
3:51PM, 93 deg, run time 11 min, then off 10 min
4:12PM, 94 deg, run time 13 min, then off 8 min
4:33PM, 94 deg, run time 12 min, then off 8 min
4:53PM, 94 deg, run time 14 min, then off 7 min
5:14PM, 94 deg, run time 20 min, then off 7 min
5:41PM, 94 deg, run time 20 min, then off 6 min
6:07PM, 93 deg, run time 23 min, then off 6 min
6:36PM, 92 deg, run time 29 min, then off 7 min
7:12PM, 90 deg, run time 24 min

I bought a cheap Radio Shack digital thermometer with humidity display. It shows a range of 50%-51% RH the whole time today, usually 51% at the start of a cycle and 50% at the end of the cycle. The condensation drain line is putting out though.

Any comments on these numbers?

Thanks everyone.

[beenthere]

Your just alittle over sized if your outdoor design is 95.

I think you have a very acurate t stat, if it was a mercury stat, you would have longer run times.
This is just a guess since you didn't post how much of a varience in temp your stat showed, and your humidity is not too bad.

Recheck your humidity when its in the low 80s, if its high then your over sized more then I said.

[typical homeowner]

Thermostat is a Honeywell VisionPro 8320, so you're correct about it being pretty accurate and not allowing a lot of variation.

[dash]

Robo,

I'd think that the larger indoor coil,being the condenser in the heat mode,would have more subcooling,and lower discharge temperatures,given the same cfms as a smaller coil.

I agree the heat gained indoors remains the same,but wouldn't the discharge air temp be lower?Kinda like the first 12 SEER units,very larger outdoor coils,low discharge temps.

[RoBoTeq]

The lower discharge temps on outdoor condensers of higher efficiency equipment is again due to the overall area of the discharge, ie; no ducting to compact the air. If we were to reduce the size of the condenser discharge while keeping the amount of air across the coil the same, the discharge temperature would be higher.

If there is more subcooling on the indoor coil of a heat pump in heat mode then there is also more heat being released, not less.

This is all pretty typical of why heat pumps got a bad rap when they were first introduced into the market. The industry was used to bumping the air volume up only for cooling purposes on duct systems that had previously been designed for heat from fossil fuel systems. These systems were notorious for being noisy in the cooling operation.

Then, we come along with the heat pump which technically should run at a higher volume of air for heat then for cooling. Since we are not running as high of temperatures across the condensing coil of heat pumps in the heat mode, we can safely decrease the amount of air in order to increas the air leaving temperatures without raising the head pressure. Heat pumps in the heat mode operate at an average of 72º air for the condensing coil because that is the average temperature homes are kept at. For this reason, we can get away with less air over the condensing coil (indoor coil) in the heat mode then we can in the cooling mode where ambient temperatures are normally much higher entering the condenser coil.

In the meantime, heat pump air handlers are still usually set for cooling air volume which is usually the reason for lower leaving air temperature from heat pump systems.

Amana had, and I wish they would bring it back, a leaving air temperature sensor that would lower the speed of a VS blower motor if the leaving air temperature dropped below the set temperature, which was able to be set from 90º to 110º. Only after the leaving air temperature could not maintain the set temperature and the VS motor was dropped to a point that was no longer safe for the refrigerant system would the auxilliary heaters then cycle on to maintain the set point leaving air temperature.