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Old 06-18-16, 12:46 PM   #1
Elcam84
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Default First 100* days with the new ac thoughts and usual minor rant...

Well we have already had a few 100* days already. Yesterday was 104*...

Man j calcs come up with a 3 ton ac for our 150 sqft house here. The problem is man j uses 100* for its calc temp which as I have mentioned before is not correct for here. Actual temp to use is 105* to 110* depending on exact location.

I ended up putting in a 3.5 ton 16 seer system. Added several returns and am going to run one to the far end of the house as well. The only way for it to get there is through the crawlspace which is better than through the attic as it doesn't get anywhere near as hot there.

I still have to run a 4" vent into the pantry and a small bathroom that's off the laundry room. They each will have a wye off the main ducts feeding those rooms. The supplier didn't have the ones I needed in stock at the time.

So far it's keeping the house at 75* but you can't do much cooking as that puts more heat into the house than it can handle and keep it 75* which is typical here. Part of living in tx is that you do minimal cooking in the summer inside. You bear the heat outside and cook on the grill.

Now when I get done with moving a wall and rebuilding both bathrooms I will be able to add more insulation in the attic and that will have an impact as back in 1960 they didn't put much up there. The old stuff is blown in rock wool made from coal slag. It has good properties except that it's the messiest insulation to use as it has lots of coal slag pellets and dust. It's worse than the dust from cellulose.


Things I would have done different if we weren't going to be moving in a year...

I would have gone with a 4 ton two stage system. Yes it's technically oversized but our summers are continually getting hotter at an alarming speed. Also if you subscribe to the global warming then you need to take that I to account which I don't see anyone in the hvac industry even giving it a thought let alone recommendations for dealing with it by increasing system sizes etc.
We are headed for another summer of 110*+ temps like we have had the last 4 years. That means easily 100+ hours over the official 100* man j temp. I do like using the man j calculator but with valid numbers.


Another thing I would do is use an indoor temp of about 70*. Just because we live in tx doesn't mean we like it hot inside. The usual interior temp is 75* which is fine nut for sleeping it's a little warm. Now with a larger master bedroom I could put in a tiny minisplit and just keep that room to 70 or less for sleeping. Remember ideal sleeping temp is around 65* according to studies.
I have spent too many summers with the temp at 78* and way too many sleepless nights because it's too warm to sleep....



Another thing I would have done if we were staying would be to put the unit in the attic instead of in the house as an upflow. It's much quieter that way. With an upflow there is no way to make it quiet because the return vents under the unit let sound from the blower right out into the hallway. You also get the slight hiss from the refrigerant when running and the low pitched sound from the compressor on startup. I hear high pitched noises very well like bad capacitors so that hiss from the refrigerant is loud to me.


I would also run the condensate to the yard if I have a good way to. The last thing to be done was to hook up the drain. So I let it drain into a bucket to see how much water it put out. Before it got hot and the ac wasn't running much it was putting out 5 gallons a day. Now with it running much more it's going to be quite a bit more.
Now that doesn't water much but hey its free water on the yard. And no pudding isn't an issue. Sandy soil and our temps it won't make a mess or run off.



For now the ac is set to 72 at night or when someone is home. If we are away it's set at 75*. Now don't get onto me how I should use a programmable t Stat and let it warm up when gone. Several real world tests including done by the DOE have shown that it does not save energy. Thus is why programmable ones no longer carry the energy star branding.
Also if I were to let it warm up it would be midnight before it cooled off to temp so it's a futile process especially if you have a "properly" sized system which is designed to maintain temp not to quick cool. However if you oversized the unit by 1 to 2 tons then you could pull it off however remember the contents of the house still need to cool as its a large thermal mass that warms up quickly but it slow to cool.

Enough ranting I guess... I'm grumpy for about 5 months of the year cause I hate being hot and getting cabin fever from not being able to do much outside. You get covered in sweat just going from car to building not to mention soaked in the car until the ac cools it off. Hint next car will have remote start...

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Old 05-16-17, 07:04 AM   #2
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sounds like you should look at:

More Insulation, Air-Sealing, Shading, Colors, Radiant Barriers.
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Old 05-16-17, 08:45 AM   #3
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Have all that what we need is less sun and more rain but cant do anything about that till we move. It's just part of living on the border of where the desert starts.
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Old 05-16-17, 10:30 AM   #4
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Well then, I guess since you will be moving in a year, the new unit will probably be considered in the selling process. I believe that a small mini split could add lots of leverage to that effect. With a well-placed unit, it could be just what the building scientist ordered. The extra capacity could tip a few scales in your favor.

I'm not just trying to empty the bank on you here. I know from your candor that you have acquired an aversion to those 1% days. I'm here to tell you there are lots of others who feel the same, and that the added zone control and capacity are not trivial. To the contrary, that extra few thousand​ BTU could quite possibly command as many extra dollars of leverage. Especially during an open house event in summer. It is considered a super attractive luxury feature by most potential future occupants.

Plus you can be comfortable for an extra year of your life. How Priceless is that?
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Old 05-18-17, 01:21 AM   #5
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I think there is some power in considering the 'step-up' rounding calculation. Let's say your load calc ends up being 26000 BTUhr with manual J. Normally you'd put in a 30000 BTUhr unit. I'd play with the numbers to see what that 2.5 ton unit does in the space specced for 26000 BTUhr. ..basically, determine the temperature spread in reverse. Often it can cover the difference. Of course this depends on the climate.

It's a little different for me. Minnesota is a place where the lakes and prevailing moisture convection brings our dew point is sky high from June through August and we have muggy wet summers where a properly sized AC is critical. I'd rather have a few days where the hottest point indoors gets a little bit uncomfortable versus a bunch of low/partial load days where I feel like I'm swimming in humidity inside. I imagine Texas doesn't have as much moisture in the air and this is less of a factor. My house was stepped up to 2 tons and I'd rather have a 1.5 ton compressor for better moisture control. Heat isn't nearly as much of a big deal when the moisture is in control. Moisture doesn't feel comfortable.
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Old 05-20-17, 08:13 AM   #6
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Quote:
Originally Posted by Elcam84 View Post
Remember ideal sleeping temp is around 65* according to studies.
There is no ideal room temperature. The reason is there is a huge variation on how people dress and what amount of sheets/blankets they sleep under, as well as body size and metabolism. The 65F thing comes from sleep studies in the 60's. Newer sleep studies focus instead on skin temperature, finding that for most people a skin temp of around 90F is ideal. To maintain that we would need to be completely naked in an air temp of around 82F. It would actually need to be quite a bit lower than that as when we are sleeping a bit less than half our bodies are covered with rather thick insulation that we call our bed, and some beds are better insulators than others (ie foam). If we add Clothes the required temp drops further, a sheet drops it further still, comforter even further, a partner under the covers further still. The ideal temp is the one that makes our bodies do a bit of work to keep core temperature up, in other words keep us just warm enough to not shiver.

All that said and I wouldn't worry about it, find the temp that you sleep well at and set it and forget about it. The reason is a recent study has shown that people who track their sleep habits sleep worse than they did before they tracked them. The working theory is that it adds one more thing to worry about at night interfering with sleep. Of course it was just one study, likely with a low population size. Even if it showed an almost perfect correlation probabilities work out to that it winds up likely only affecting less than 10% of the population. Even so, we worry about too much crap as is, worrying about optimum sleep is just really not all that important.
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Old 08-19-17, 06:41 PM   #7
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Quote:
Originally Posted by MN Renovator View Post
I think there is some power in considering the 'step-up' rounding calculation. Let's say your load calc ends up being 26000 BTUhr with manual J. Normally you'd put in a 30000 BTUhr unit. I'd play with the numbers to see what that 2.5 ton unit does in the space specced for 26000 BTUhr. ..basically, determine the temperature spread in reverse. Often it can cover the difference. Of course this depends on the climate.

It's a little different for me. Minnesota is a place where the lakes and prevailing moisture convection brings our dew point is sky high from June through August and we have muggy wet summers where a properly sized AC is critical. I'd rather have a few days where the hottest point indoors gets a little bit uncomfortable versus a bunch of low/partial load days where I feel like I'm swimming in humidity inside. I imagine Texas doesn't have as much moisture in the air and this is less of a factor. My house was stepped up to 2 tons and I'd rather have a 1.5 ton compressor for better moisture control. Heat isn't nearly as much of a big deal when the moisture is in control. Moisture doesn't feel comfortable.

It's quite humid here year round unless you are in west TX which is desert. Today it's pretty cool already. High was only 101 and it's already dropped to 92* at 5:30 which is very early for it to be that cool but the humidity is 65%....

The few places I have been on the coast and they complained about it being too humid and oversized units were actually cases of not setting the thermostat low enough. They were keeping it at 78 to 80 and yeah its not going to dehumidify because it's not set cool enough so it isn't running enough.

So far our ac has been working great. The electric usage is drastically less than the old system and the house can be kept at a comfortable mid to low 70s. The only thing I had to do was replace the capacitor which I should have done on install because the factory installed ones are horribly cheap. Spend the cash for a good made in us capacitor. Will last the life of the system and weighs much more than the cheapies.
If we were staying I probably would have gone with a two stage compressor as I prefer how they continually run instead of cycling as much as a single stage. Also would go with a unit that I could lower the continuois fan speed more. The continuous circulation makes for improved comfort however increases running costs.
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Old 08-19-17, 11:06 PM   #8
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A variable speed motor is a viable option for an upgrade to your air handler unit. If you're still having any humidity removal problems, it's definitely worth looking at to increase comfort levels. It's possible to DIY a motor speed control on the existing motor, but the reliability of what is installed really depends on the existing motor.

A few other members have modded their units in this manner. Just read around on the forum and you'll find lots of stories and conclusions drawn from the process. Spoiler: everyone was satisfied with the new modes of operation.
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Old 08-20-17, 11:21 AM   #9
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I have an ecm motor but it still doesn't run at a slow enough speed well not what I want it to run at. No problems with moisture removal. Sitting at 45% except for for a few minutes after someone takes after shower. Not everything gets pulled out with a fart fan and the outside air you are pulling in has allot of moisture.
I'm not the biggest fan of ecm motors as they do fail allot more than traditional motors and some are a $500 motor... Basically buy a new furnace price... Ecm motors also have false start issues as well. Some will have trouble starting to and go through the starting sequence 2 to 3 times before it starts.

For houses that have moisture issues it's recommended to use a dehumidifier instead of relying on the ac to do it all.
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Old 03-17-20, 07:05 PM   #10
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To add an update. After talking to a couple of the HRV and ERV companies and others non recommend either unit for our climate as it's just too humid and often like now there is no escape 66* 95% outside and 73*62% inside...

All recommend using a ventilating dehumidifier here. They can either recirculate air in the house or bring in outside air and dehumidify it before ducting it inside. Nice units and fit the need here but pricey at $1600.
I had planned on installing one this spring but... Current events have derailed that as the better half and daughter are both flight attendants. It's likely daughter will be laid off but the better half should be ok as she has 27 years of seniority. We are all ready for this over reaction to a bug to be over with.

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