The obvious checks would be a good digital thermometer that you can use to check temps around the house and compare to relatives.

The 2nd thing would be a digital humidistat to see what the humidity is.

Honestly, you sound still a little oversized. 3-4 cycles per hour maybe typical but far more than ideal.

Not certain how many speeds you have on blower but I would lower the speed and evaluate system before doing anything else. Another observation is that the 2.3 ton load calc was obviously not correct.

Try the blower speed first and post back.

IMO

I am going to do that tonight and determine whether or not the room temps are in fact 22C. The load calc I believe is probably quite close to what the house needs as builders and other home owners on the street have units that are either similarly sized or bigger (it seems like contractors here like to oversize). I have an old analog humidity meter and it looks like the house is around 35-40%. I'll pull out a digital one tonight to get some exact figures.

David_cary to clarify the cycle times it was 27C outside yesterday and my house was set to 22C. The a/c would come on for 12 minutes and then shut off for 12 minutes and repeat that over the course of the house so by definition it would cycle just over 2-3 times / hour. This would make sense as the house has already reached it's set point so the running is to simply maintain that temperature. Had I sized the a/c up to what my colleage had mentioned then I think I would be definitely short cycling a lot b/c of the added sensible heat removal capacity.

Tigerdunes I have 4 speeds on my blower. High, med-high, med, low. I have already occupied the med-high and med speeds for heating/fan circulation mode but I'll play around with the wiring to change up the speeds.

I still wonder if TXV vs. fixed orifice has anything to do with what I'm observing.

I would set cooling fan speed at medium. You should get better dehumidification and possibly change your cycles per hour. 2-3 CPH would be optimum.

Back to the load calc. Depending on your design temperatures both inside and outside, 2.3 tons can not be correct unless you are seeing your system run continuously at high outside temperatures. Are you?

I would run the new blower speed for several days and make periodic observations as far as humidity, CPH, run times, indoor comfort, etc.

BTW, you are certain dealer installed a two ton condenser with correct evap coil?

Post back your findings.

IMO

I will change the speed to medium/medium high today to see how that will pan out. I will also need to take temperatures throughout to home to see how balanced things are. Overall the system isn't performing as badly as I might be describing, I just think that it should be able to remove more water from the air than it feels like (granted it does feel drier than it ever has in the past prior to installing a/c).

When it is 32C outside and the a/c has been off all day it takes the system about 2.5 hours to pull the inside temps from 28C to 23C and remove the moisture/latent heat. Hard to say. The hotter it is then the longer it runs. It's rare that we hit 30C for long periods of time 26-28C is more common for about 6 weeks out of the year. I'm quite certain it is not short cycling. The most CPH is 4 and sometimes it has been 2-3 times when it's been very warm.

If I recall correctly, the day my colleague came by to verify the charge he got these measurements.

Suction line temp before entering condenser = 50-52F
Air temp exiting evaporator 52F
Air entering evaporator coil: I didn't see this reading but the room above the furnace where the return plenum which is pretty darned close to the evap inlet was should be 23-24C. I don't know the wet bulb temp.
Outside ambient: 24C Didn't feel too humid that day.
Suction pressure: ~125-150PSI
Liquid: ~280-300PSI
Refrigerant: R410a
System was able to start and stop in reasonable time frames - wasn't short cycling like I've seen some homes and their a/c systems.

Coil and condensor are a matched 2 ton coil with the right orifice (b/c he said he doubled checked and my dad was there overseeing the install and he also like myself does have some understanding of a/c systems and how they're installed).

Thanks,

Medium, not med high!

I will change the speed to medium/medium high today to see how that will pan out. I will also need to take temperatures throughout to home to see how balanced things are. Overall the system isn't performing as badly as I might be describing, I just think that it should be able to remove more water from the air than it feels like (granted it does feel drier than it ever has in the past prior to installing a/c).

When it is 32C outside and the a/c has been off all day it takes the system about 2.5 hours to pull the inside temps from 28C to 23C and remove the moisture/latent heat. Hard to say. The hotter it is then the longer it runs. It's rare that we hit 30C for long periods of time 26-28C is more common for about 6 weeks out of the year. I'm quite certain it is not short cycling. The most CPH is 4 and sometimes it has been 2-3 times when it's been very warm.

If I recall correctly, the day my colleague came by to verify the charge he got these measurements.

Suction line temp before entering condenser = 50-52F
Air temp exiting evaporator 52F
Air entering evaporator coil: I didn't see this reading but the room above the furnace where the return plenum which is pretty darned close to the evap inlet was should be 23-24C. I don't know the wet bulb temp.
Outside ambient: 24C Didn't feel too humid that day.
Suction pressure: ~125-150PSI
Liquid: ~280-300PSI
Refrigerant: R410a
System was able to start and stop in reasonable time frames - wasn't short cycling like I've seen some homes and their a/c systems.

Coil and condensor are a matched 2 ton coil with the right orifice (b/c he said he doubled checked and my dad was there overseeing the install and he also like myself does have some understanding of a/c systems and how they're installed).

Thanks,

On sizing - if it is 32 out and that is a rare high - we'll call that design temp, then a correctly sized system would not be able to cool the house (much) at that outside temp.

My definition (which maybe a tiny bit off) is that a properly sized system at design temp can maintain 76 (24.4 C) as a inside temp. It can't cool the house to 22 and it can only maintain 24.4C - ie it can't get the house from 27 to 24.4.

So by my definition, you are still significantly oversized presuming that 32 is your design temp. A design temp is one that is exceeded less that 5% of the time.

Your CPH is partly a function of the hysteresis of the stat. A better measure of sizing is duty cycle - and it sounds like you are at 50% - on half the time - on a hot day. Ideally you are close to 100% on a hot day at least in the afternoon.

A 12 minute cycle is not anything to be satisfied with irregardless. A 30 minute cycle is better.

Humidity of less than 40% is usually very comfortable and not a real issue with humidity control so the cycle length is probably not the issue - if that humidity is correct.

In the end, I suspect your stat is off or it is in a bad location that is not representative of the interior temperature.

In the Southern US, our typical design temp is 96 and our interior goal is 78. And as a population we are oversized 99% of the time.

Hi David, interesting feedback.

I'm not sure what the design temperature would be for the system but I can tell you that the system we have can without too much effort pull the house temperatures down to 22C and maintain it by cycling on and off.

I just went out to pickup an HVAC Psychrometer to do some measurements for dry/web bulb temperatures so that I can determine if my stat needs to be replaced or have it's offset changed to better reflect what actually is.

I would like to see a design temperature of 32C with a target temperature maintained at 23-24C.

Oversized is a gross understatement here in Calgary. The reason why I say this is that strange as it may be we have homes that are 2000 sq ft with huge 3 - 3.5 ton systems on them while in Saskatchewan and Manitoba the same homes have these tiny condenser units sitting on the side of the house. This suggests to me at least that the mid prarie folks know how to make a/c systems operate more efficiently vs. here in Calgary where high humidity is so rare that instead contractors oversize so that any sensible heat can be removed quickly as moisture in the air typically isn't a problem.

Well if it is dry, then oversizing doesn't hurt as bad so there was no need to actually think about an install.

Hi David/tigerdunes,

So I called up the installer and he suggested I slow the blower right down on the furnace to match the CFM flow of the coil. He says that the tonnage to CFM flow should be 400 CFM for every ton of cooling.

Well my blower was on max power and my furnace is a lennox g40uh36B-090 furnace and looking at some specs on the furnace it would appear that on full power that furnace can blow 1500 CFM assuming there are no restrictions. My furnace is a 4 speed blower so I opted to use the medium blower speed (second slowest - lennox specs say the range of CFM is between 750 - 1000 CFM depending on the restriction. Well after making that change it would seem that the system is now running only 1-2 CPH and the cooling is less muggy. I got myself a psychrometer and the indoor RH is 45% with a dry bulb temp set at 22C. Coil temp is 8.8C. I will run the a/c like this for a week or two and see how the system fairs up and if all is good then I'll have my installer come back to re-adjust/recheck the charge to make sure the superheat falls within spec.

Today is a rather moderate day (only 23C outside) but the a/c ran for 45 minutes straight and more water is coming out of the coil too.

s there any risk at running my blower at the 2nd lowest speed? Doesn't seem like the coil would freeze up as the output temps are still near double digits.

I think I said that.

Your furnace has a three ton rated blower. In fact, I would strongly suspect on the heating side, you are oversized.

However, for a two ton condenser, 800 CFM setting should be correct.

Keep us posted.

IMO

One other thought.

A side benefit to lowering speed is system should be quieter.

IMO

I was looking at the specs of my furnace and I think medium low even at the worst case static pressure of 0.9 in w.g. I would still be getting 710 CFM across the coil at the worst case which still falls within the 350 CFM minimum / ton of cooling. I'm only stabbing in the dark here but at 0.5 in w.g. the CFM rate for the blower speed I have selected is 965 CFM which should fall well within the CFM flow rates as required for a 2 ton system. What was interesting was that in the installation manual it states that the furnace was designed for 2-3 tons of cooling which I would equate out for the 4 speeds of the blower. Low speed would be suitable for the smallest of a/c coils (2 tons in my system's case) to the fastest which would suffice for the larger 3 ton coils). I've opted not to use low b/c I don't know what the static pressure is plus leave some headroom to prevent coil freeze up due to reduced air flow.

Thoughts on this?

I agree.

Start with medium.

Freeze ups should be avoided. Return filter should be clean or changed out.

I would run the new blower speed for several days and make periodic observations as far as humidity, CPH, run times, indoor comfort, and note thermostat setting and outdoor temp.

IMO

Is the fan speed the same for both heating and cooling modes? If it is then you want to verify that lowering the blower speed is not causing the furnace to operate above its maximum temperature. This will cause the high limit switch to trip. It could also cause the heat exchanger to crack.

Your furnace may have independent blower speed for heating and cooling. The installation manual should have this information.

tigerdunes, I will do what you said and run the system for a few days in the manner that it is setup now. Just to clarify I am running medium low and not medium high.

Mike_home I've left the heating circuit on default medium high b/c it shipped from Lennox setup that way. The cooling fan circuit is separate and I'm running medium low.

The highest speed isn't used and the lowest blower speed is on the circulation fan circuit.

So in essence my furnace is setup from the lowest speed (circulation fan), medium low (for a/c) and then medium high (heating).

I will get the installer to come adjust the charge next week when it is supposed to hit 28C. As it stands he already knows the system is slightly overcharged b/c the coil came precharged for 15 ft of line where as my system today is using 12 feet.

Not sure how he's going to remove the excess charge without upsetting the balance of the refrigerant mix.

So yesterday buddy comes over to look over things with the a/c system and I think we've got things nailed down properly now.

The superheat for the given ambient temperature and heat loading from the indoor coil was way off (5F) vs. the 14-15F that it was supposed to be so he had to remove some of the refrigerant (I was quite surprised how little he had to remove to get the superheat up) and we even went as far as measuring the furnace's CFM flow rating using a differential manometer. I'm pushing roughly 1000CFM across a 2 ton coil so which is a tad bit on the high side but my colleauge says it's a margin of safety for the a/c to not freeze over as we have relatively little humidity in the air would means that on the cooler days we wouldn't be heat loading the coil enough which could lead to freeze up.

I personally would like to try running my furnace on the lowest speed to get the 855 CFM but I'm not sure how that will affect the superheat. Presumably I would imagine that if a system is charged properly using the superheat method for fixed orifice systems that blower speed shouldn't dramatically impact the superheat values to the point where they're completely out of whack. I would guess that superheat would rise but isn't that sort of a given? I mean hotter days for example would increase loading so therefore superheat should rise no? For the record the pressure reading on the manometer with the furnace on medium low with a 3M 1500 series filter installed has a -0.44 in wg static pressure difference. With no filter the static pressure diff changes to -0.55.

Humidity was still somewhat of an issue yesterday night when it was raining but it was quite cool outside. I had to drop the tstat to 21C to force start the a/c on but after just 20 minutes the house was nice and dry and less stuffy.

Just for the sake of my understanding does TXV technically do any better or worse job of temperature/humidity control over a fixed orifice system IF both systems were installed properly and charged to near perfection?

I have a friend that is looking to install a/c and his contractor insists on having TXV and says that fixed orifice is evil and should never be used. I find that rather extreme to make a claim like that. I've tried to do my own research online and although it's a given that TXV is the way to go I think it has a lot to do with the fact that it will better protect the compressor from liquid flooding + it's more forgiving for techs that do an incorrect charge on the system - critical charge isn't nearly as important on a TXV system vs. fixed orifice.

Thanks,

TXV meters refrigerant more efficiently. TXVs can fail prematurely. Bad bunch not too many years ago.

You are fretting over this issue way too much...

Be careful of 3M filters. I would not use them...too restrictive not to mention the cost of anything from 3M...

Too bad your system does not allow for DOD...

IMO

I don't understand why your buddy insists on pushing 1000 CFM over a 2 ton coil. If the charge is correct the coil should not freeze. The guidleline is 350-400 CFM per ton, therefore you should be in the 700-800 CFM range. You will have better humidity control on warm rainy days.

I also don't understand the static pressure readings. I have always thought the static pressure reading to be a positive number with 0.5 WC to be ideal. The static pressure appears to be increasing by 0.11 WC with the filter. If this is true, then that's quite good considering the 3M Filtete filter is very restrictive.

I am no expert on TXV valves, but I thought installing them was a standard practice on new equipment with especially multi-stage ACs. I have never heard of a down side of installing a TXV other than additional cost.

How old is this system? Furnace and AC?

R22 or 410!

It appears to be low end based on furnace model.

IMO

I think that he's playing it safe to ensure that the airflow isn't low enough to cause problems should the filter over time plug up.

Put it this way. I would have NO issues changing the blower speed over to the slowest speed to get to the target 350-400 CFM. In fact I would like to but in the act of playing safe I opted to not push the issue.

So here is the big question: If the superheat charge was perfect at 1000CFM then will changing it to 800-860 CFM drastically impact the superheat to cause and undercharge situation? I would imagine that slowing the system down 200 CFM would most definitely add more "superheat" to the system therefore causing the suction temperature and pressures to be different (this is where TXV saves the day by keeping the overall superheat constant in the coil).

Not sure why it was a negative number for static pressure BUT it could be the way the hoses are setup on his magnometer. He put a probe just before the coil and then the other hose probe to the return plenum before the filter. Calibrated to zero and then turned the system on. I guess the pressure would be negative because the furnace is "restricted" by the filter and trying to "suck" air through the blower up through the ductwork. By sucking it's creating a vacuum and causing a negative reading?

Tigerdunes, I mentioned my equipment and system age at the beginning of the thread but here it is anyways:
Furnace is a 10 year old Lennox G40UXH-B 036-090
A/c is a 2 ton fixed orifice r410a split system that was just installed.

Other relevant info that might be useful include:
Furnace blower capability: 1500 CFM max to as low as 750CFM. Furnace installation instructions clearly state air handler in furnace is capable of running a cooling system from 2 - 3 tons. Furnace for sure is oversized but up here in Canada esp in Alberta where the nightime temps in the winters can dip as low as -38C I think being oversized is deliberate.

I can shift the blower speeds to best match the spec of the system but I will say that I'm concerned now that my superheat that my buddy and I worked to get nailed down perfectly may be affected and that the compressor because of the higher superheat will fry the compressor b/c of lack of cool refrigerant. Maybe I'm wrong but if someone could shed light on my thinking that would definitely help.

thanks,

If it is a humid climate than without a doubt TXV all the way because they keep the coil at that sweet spot for removing humidity better over a wide variety of outside and inside temps where a piston type will have a much smaller window of peak efficiency which really only becomes evident in humid climates.

I think the blower settings will be able to get you dialed in now that the charge is correct.

"I think that he's playing it safe to ensure that the airflow isn't low enough to cause problems should the filter over time plug up."

If you changed your filter on a regular basis you should not have a problem. The air flow passing over my coils has been at 350CFM per ton during the past 4 summers. I have yet to experience a frozen coil.

Hi countryboymo, yes the charge was dialed in perfectly as I was there to witness it first hand plus my colleague was quite patient with my requests as well as him adjusting things accordingly. The target superheat that day was calculated to be 14.5F at the compressor (61 ID WB and 73F OD DB) with approximately 900-1000 CFM across the coil. We tried to slow the blower speed down to the rated 800 CFM for the 2 ton system but I found that the upstairs wasn't cooling enough in a reasonable timeframe so we left it at medium low. Yesterday the temperatures were in the mid 80s (that is as hot as it EVER gets here) with relatively low humidity (I think it was maybe 40% which is typical for this time of year). I started the a/c and within 30 minutes the house was noticably cooler even those the sensible heat temperature didn't drop for at least an hour before. So the system I know is doing it's job cooling the home.

I posted another question regarding the sweating of the suction line so I might as well as here again:

If the heat load on the evaporator coil is high and the charge is spot on then would it be safe to say that there is not going to be any sweat on the suction line/service valve area of the condenser? I would imagine b/c of the high heat load that the suction temps would be higher therefore no sweating (it was cool but definitely not beer can cold). As the system ran for about 1.5 hours and the house temperature gradually dropped then you could start to see condensate come out of the evaporator AND you could see small tiny droplets of sweat forming on the suction line at the compressor. To be clear the home cools at a reasonable rate and nowhere were we ever uncomfortable or thought the a/c was not working right. I'm more concerned with compressor cooling more than anything but since the suction line was still somewhat cool when the heat loading was higher that it was probably fine. I just know that when the system was overcharged the week before that within minutes of starting up the system that the condensate and sweat would just start quite fast after starting up whereas now it seems to take it a while. Not so surprisingly the system after the charge adjustment in fact performs its best now. 30 minutes and the perceived cool can be easily felt vs. the 45 minutes - 1 hour the week before when it was slightly overcharged.

I could be wrong, but if your air is dry you are not going to see any moisture accumulating on the coil. A humidity of 40% is fairly dry for the summer. Now it could be the high side is not as cold as it used to be, but you stated the system was only slightly overcharged. I am not sure if that is going to make a big difference. You are relying on your's buddy's guages as being accurate and he knows how to interpret the readings at a given temperature.

I grew up in an old house with a basement in New York City. The basement would bet so humid in the summer that the cold water pipe would sweat!