Is it true that matching a 2.5 T outdoor unit (heat pump) with a 3 T indoor coil/blower (bigger coil) will yield better dehumidification? Or will it cause other problems. My current system (which is being replaced) for the last 19 years was a matched 2.5 T inside and outside and I had no issues to speak of.
Bigger indoor coil = better dehumidification?
Unclev
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Is it true that matching a 2.5 T outdoor unit (heat pump) with a 3 T indoor coil/blower (bigger coil) will yield better dehumidification? Or will it cause other problems. My current system (which is being replaced) for the last 19 years was a matched 2.5 T inside and outside and I had no issues to speak of.
Larger indoor coil coupled to smaller compressor and condenser outdoors does NOT yield improved dehumidification.
Why? Because the indoor coil will run warmer. The smaller compressor can't get the evaporating pressure low enough to deliver the dehumidification capacity a larger indoor coil is touted to provide.
Match the system with a TXV and get your house evaluated for leaks in the walls, ceilings, etc. You will then have all the dehumidification capacity you could dream of, short of a ventilating dehumidifier.
Why? Because the indoor coil will run warmer. The smaller compressor can't get the evaporating pressure low enough to deliver the dehumidification capacity a larger indoor coil is touted to provide.
Match the system with a TXV and get your house evaluated for leaks in the walls, ceilings, etc. You will then have all the dehumidification capacity you could dream of, short of a ventilating dehumidifier.
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+1. You will get the opposite results. Smaller coil = lower coil temperatures with the same size compressor. IT wil also cool off quicker, meaning it gets wet sooner.
If you drop 10 ice cubes into a 20oz glass vs. a 30oz glass, which will get colder and sweat more? At some point, if the glass is large enough or you reduce the number of ice cubes, it won't sweat at all. On a coil, this is called a dry coil. WIth a dry coil, you do get more capaicty and effiiciency in part because there's a lower air pressure drop (less resistance) across teh coil, so your SEER rating goes up, but because you can't control humidity, your overall energy useage ogoes up because you set it colder ot be comfortable.
Equally or even more improtant that coil size is system size. A properly sized system will rn continously in the hottest weather and might even fall behind a little, but will run the most efficiently and remove the most humidity.
On my own home, I've seen an a significant improvement in energy savings above what the improvement in equipment efficiency ratings alone would have predicted. Similarly, in my last home I saw the opposite when going form a 2 ton to a 3 ton 2 stage system (I didn't know better then). Despite going from 10 SEER to 15 SEER, I actually saw an increase in my bills despite a more mild summer. In comparison, I'm now on track to have a lower July bill than June electric bill despite a full week with the high temps we all saw.
If you made any energy efficeincy improvements like insulation, low-E windows etc. in the last 19 years, it possible that a load calculaiton may show you only need a 2 ton system now. You'll have a quieter system, that will run longer, use less energy and give more even temepratures and lower humidity.
If you drop 10 ice cubes into a 20oz glass vs. a 30oz glass, which will get colder and sweat more? At some point, if the glass is large enough or you reduce the number of ice cubes, it won't sweat at all. On a coil, this is called a dry coil. WIth a dry coil, you do get more capaicty and effiiciency in part because there's a lower air pressure drop (less resistance) across teh coil, so your SEER rating goes up, but because you can't control humidity, your overall energy useage ogoes up because you set it colder ot be comfortable.
Equally or even more improtant that coil size is system size. A properly sized system will rn continously in the hottest weather and might even fall behind a little, but will run the most efficiently and remove the most humidity.
On my own home, I've seen an a significant improvement in energy savings above what the improvement in equipment efficiency ratings alone would have predicted. Similarly, in my last home I saw the opposite when going form a 2 ton to a 3 ton 2 stage system (I didn't know better then). Despite going from 10 SEER to 15 SEER, I actually saw an increase in my bills despite a more mild summer. In comparison, I'm now on track to have a lower July bill than June electric bill despite a full week with the high temps we all saw.
If you made any energy efficeincy improvements like insulation, low-E windows etc. in the last 19 years, it possible that a load calculaiton may show you only need a 2 ton system now. You'll have a quieter system, that will run longer, use less energy and give more even temepratures and lower humidity.
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I think you'll find the opposite. A only slightly undersized system set at the correct aiflow setting, will have extremely long run times will manage the latent load, especially in part load conditions, but fall behind in sensible capacity.
Many times systmes are accused of being undersized because of hte use of setbacks, or ariflwo being set too high and having poor latent capacity. We talk a lot about 400CFM/ton, but in much of the country, it's humid enough in summer than 350CFM/ton is more appropriate. Even better is duhumidify on demand. It a properly sized systme you won't need it if loads are above about 1/3-1/2 desing conditions. Below that you'll need a lower sensible ratio.
SEER means nothing if the system is not installed and charged properly, and the ducts leak like crazy.
And I have yet to find a way to field verify real-time SEER performance. EER, yes. SEER, no.
We use a/c to be comfortable. If the system isn't delivering comfort, most people respond by trying to make the system work harder. The system may be working very hard, but it's fighting a losing battle due to leaky or restrictive ducts, and/or improper refrigerant charge. Now how is that saving energy and money?
And your OP coincides with this thought...you choose a larger indoor coil hoping it will deliver more comfort, but when it doesn't dehumidify like you want you run the system longer and colder to get where you want to be. Again, how is that saving energy and money?
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I don't know how you could since SEER is some goofy weighted formula that looks at various operating conditions.
I wish they just listed the units with a COP in cooling (and heating if a heat pump) at multiple, real data points. Let's use real numbers too. So 74F, 50%RH indoor conditions and then outdoor temps at maybe 70F, 80F, 90F and 100F. So if you live in Illinois, the 90F range, in Michigan, the 80F range. In Texas, the 100F range, in the pacific northeast, the 70F range.
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This question has 3 answers, yes, no, and sometimes.
The new high efficiency a/cs have very large coils compared to the old a/cs. Many are 2X larger. To complicate the answer, most of these multispeed systems use this very large cooling coil with compressor are reduced capaicity up to 60%. Yet they do a good humidity control at 40% load conditions.
Using large cooling coils is all about managing the air flow verses the cooling capacity. The same is true for the new ultra efficient dehumidifiers. A/cs remove 1-2 pints per kw. While dehumidifiers vary from 1-8 pints per kw.
The "no" anwer problem starts when the any of these devices are short cycling. The larger the cooling coil, the more moisture is retained that will evaporate back into the home. 1lb. of moisture will raise the indoor %RH of 900 sq.ft. of home 10%RH. This happens in the first 45-100 mins. of the off cycle. The larger the coil, the more moisture is retained on the coil and in the pan.
In the end large coils can remove more moisture per ton of cooling with proper air flow but retain more moisture at the end of the cycle.
Using over-cooling to control moisture is the most costly form of dehumidification, plus it is uncomfortable and and unhealthy because of condensation in walls exposed to high outside dew point air.
Hope this helps to understand a very comples issue that tends to be over-simplified.
Most green grass climates are best served by a simple 13-15 SEER a/c with a proper sized whole house dehumidified. You will have a moderate investment, absolute <50%RH through all of the variable weather conditions. Also when the any question arises about "is the system working", you will be able to get a service tech that will actually understand how everything works. These multispeed systems are complex very difficult and expensive to service.
The VS fan is about as complex as I care to get right now.
Regards TB
My point precisely. At least with EPA estimated miles per gallon information available for cars, the end user can verify if his vehicle is actually performing near the estimates. With SEER and HVAC, no way. Customer is told if he buys higher SEER he's buying higher efficiency without compromise to comfort, but we know that's not always the case, and there's no way for the customer to verify himself first hand if his system is actually delivering rated SEER.
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Like MPG in cars, the test conditons may not match how most people operate their systems.
It's funny, when you buy some motorcycles, such as a BMW, the fuel consumption rating is shown at steady state conditions at 2 different common crusing speeds. I wish cars were that way too.
It's funny, when you buy some motorcycles, such as a BMW, the fuel consumption rating is shown at steady state conditions at 2 different common crusing speeds. I wish cars were that way too.
Far too many are oversizing high seer units which destroys seer ratings & humidity control; airflow will also be less efficient.
When the system is sized right & you have a TXV metered indoor coil along with VS blowers & dehumidification thermostats, all of those components when used wisely can help occupants get to their comfort levels at the least cost.
When airflow is lowered, a TXV will slow down the flow of liquid refrigerant into the coil, adjusting it to its superheat set-point which lowers Btuh output thus, increasing the length of the runtimes.
CPH & Temp swing adjustable differential RM-THs can also help by increasing runtime lengths; of course, it will be off longer, too....All the above helps to increase SEER; which I don't put much weight on either...I hope they don't make the 16-seer the minimum seer!
When the system is sized right & you have a TXV metered indoor coil along with VS blowers & dehumidification thermostats, all of those components when used wisely can help occupants get to their comfort levels at the least cost.
When airflow is lowered, a TXV will slow down the flow of liquid refrigerant into the coil, adjusting it to its superheat set-point which lowers Btuh output thus, increasing the length of the runtimes.
CPH & Temp swing adjustable differential RM-THs can also help by increasing runtime lengths; of course, it will be off longer, too....All the above helps to increase SEER; which I don't put much weight on either...I hope they don't make the 16-seer the minimum seer!
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