High-SEER mini splits instead of WSHP? - Page 2

DEnd · 04-14-17, 02:57 PM

Quote:

Originally Posted by oil pan 4

Inverters don't short cycle.
I wasn't going to run all of them at once.
The idea is to leave the air conditioner off all day then turn it on and cool off the house fast in the afternoon.
In the past I have used air conditioners that should have cooled but didn't and ended up leaving them on all day.

Yes they do. They have a cycle range to something like 20% capacity (some go as low as 10% or so) if the cooling needs are below that they turn off, and they have relatively high vampire draw when they aren't running. What's more when they turn on they turn back on to full bore and then throttle down. That's because their evaporator coils get heat soaked and for the mini split to function properly the evap coils have to get down to proper temperature first.

Why turn the A/C off? if you are only gone for 8 to 12 hours it's better to leave the A/C on than to have it play catch-up, especially if you have a VRF unit of some kind (like an inverter driven mini-split). The temp set back works in many houses because the system is so poorly designed (including the building envelope).

jeff5may · 04-15-17, 07:15 AM

The main reason for temperature setback arises from traditional gas furnaces. As you know, nearly every gas furnace in a reasonably sized single family home is oversized. The less gas burned, the lower the bill. When they operate, they blast out high-grade heated air. A quick burn causing a drastic temperature rise, followed by a not-so-quick coast to below setpoint, describes typical operation.

Many older folks have been conditioned to accept this mode of operation as "ideal". My parents are two of them. We lived in Colorado, where during clear skies, when the sun went down, the temperature immediately dropped. The heat literally flew away to space all night. The thermostat on our home heating system had like a 7 or 8 degree deadband, so the furnace ran for a little longer when it kicked on. My father was a proponent of temp setback, and during those clear winter nights, the thermostat got set back like 10 or 20 degrees around dusk. I caught some sort of ear, nose, or throat disease about every year I was growing up, until I put a waterbed in my room. For some reason, all the other kids wanted to sleep in my room. It just felt more comfortable than the rest of the house.

Besides the obvious health issues, temperature setback becomes less effective when you match your heating and cooling equipment to the home load. A "tiny" heat pump (or air conditioner) isn't able to quickly change the air temperature like a blast furnace (or blast freezer), so the short run period mentioned before goes away. The thermal mass and insulation/infiltration play a larger role in maintaining comfort levels, as well as a more responsive thermostat. Most modern systems include a thermostat with a 1 or 2 degree deadband and multiple stages of control. Yes, you still reduce the temperature gradient between indoors and outdoors with temperature setback, so any energy usage due to setback is still reduced while the unit sits idle.

When the thermostat is returned to "normal", it takes a LONG time for the building to recover. The closer your HVAC system is sized to your actual heat load, the longer it takes the system to overcome the change in setpoint. On days where the temperature changes quickly (not uncommon in the southwest), the change may exceed the capacity of the system. The result is felt at the worst possible time, normally on some holiday weekend when you are home all day or have company. My parents always ran the fireplace in the evening, rather than not setting back the furnace.

The moral of the story: if you are going to employ thermostat setback, have a backup source to fire up and prepare to shed or add clothes to maintain personal comfort. Or you can just sweat or shiver. Because oversizing your HVAC system is a waste.

jeff5may · 04-15-17, 08:02 AM

Another phenomenon to consider, especially with air conditioning in summer, is thermal radiation and how it relates to comfort. Just cooling the air quickly is easy. When this happens, the only time you feel comfortable is when there is wind. The reason being is because all the "stuff" around you is still hot, and is in fact radiating its heat into you. Just having cool air present is not enough to maintain personal comfort, the mass inside the envelope has to be cool as well. As stated in the post before, it takes a LONG time to draw the extra heat out of the thermal mass inside the envelope of the structure. If the system is sized within a factor of less than 150% of your design heat load, there is more energy stored inside the envelope than can be quickly regulated by adding or removing heat with the HVAC system. If there is much infiltration, it quickly overcomes the limited capacity of the system.

Many retail stores (think dollar store or mexican restaurant) suffer from this condition. During spring and fall, these venues are usually very cozy, since the system is not experiencing drastic outdoor weather changes. But this Easter weekend, here in Kentucky we are getting lots of sun and clear night skies. Just when the HVAC system has a chance to recover from the 90 degree day, the setpoint changes to above 75 degrees, and all that cool night air is not allowed to draw all the heat out of the hot product being restocked onto shelves. When the thermostat resets to 68 degrees in the morning, the system only has a couple of hours to move literally 100 tons of heat outdoors before the automatic sliding doors start moving. By noon, the HVAC system is ineffective. By 2 or 3 o'clock in the afternoon, the sliding doors have rendered the venue uncomfortable, and all you can do is pray for clouds without rain in them. On a positive note, the electric bill is 20% less than without setback, even counting the little fans all the cashiers are blowing in their general directions.

oil pan 4 · 04-15-17, 08:24 AM

That's exactly why I'm going over sized to be able to cool the house and everything inside down fast.
Running the A/C all day when not home is just wasteful.
If I was going so far oversized with an inverter to the point where it wouldn't work right I would have to put like a 2 ton in the bed room.

We tried this on my friends house. The house flipper that had it before him put in a new barely large enough 2 ton heat pump. First he tried just leaving the 2 ton off all day then turning on when he got home, the 2 ton wouldn't turn off till 9 or 10 at night. He replaced the heat pump and air handler with a 4.5 ton. Leaving the 2 ton on all day versus turning the 4.5 ton on when some one comes home has cut his power consumption by at least 1/3 and up to 1/2. He said it paid for its self in 2 years. That was back in 2010 or 2011.

jeff5may · 04-15-17, 08:31 PM

We did the same thing with a rental property. The 14x70 aluminum box trailer had a "standard" sized gas furnace and a "premium" sized packaged air conditioning unit. After the furnace developed pilot problems, we swapped it for a "standard" double wide furnace. Everyone has been very happy with the extra heating capacity. I imagine it costs more to heat now than it did, but it's not a heat pump.

If you are going to employ setback strategies, oversizing your HVAC unit will allow the quick recovery that this strategy dictates. Make sure to install a variable capacity system that can throttle back its output when the setpoint is reached.

WyrTwister · 06-06-17, 09:48 PM

As for as purchase cost and SEER ratings , of Mini-Splits , it has been about 2 years since I bought and installed one . So , I may be somewhat behind the curve .

The MS's will be cheaper than WSHP's , to install . Maybe cheaper to purchase .

MS's are available in amazing SEER ratings . And with hear ratings that go down to pretty low Outside Air Temperatures .

Do you plan to contract out everything of do some / all via self install ?

Let me ask this . Is your existing HVAC system still functional ? If so , start by installing one MS , of the highest energy rating you can afford . Maybe in a space that presently is poorly served . See how you like it . Remember , you do not have to do it all at once . And it will take the load off of equipment that may be just limping along .

Or start out in an area that will allow you to completely obsolete one of the smaller existing HVAC units .

As for as sizing is concerned , ductless MS;s do not suffer from duct losses . And the new inverter compressor drive technology will ramp op capacity / ramp down capacity , as needed .

You can use multiple MS's to zone hour heat / cooling to fit your varying needs / schedule . Multiple units also give you redundancy . And if you can design the " system " so all or several of the units are identical , you might buy one extra unit ( indoor / outdoor unit ) for a standby / spare ? If it is critical to get a unit up and running , should one go down .

As far as the indoor units , wall mounted units will be cheaper to purchase , but they make them that you can install in the attic , blowing directly down into the living space .

Try one , you will like . Both of ours are 12,000 BTU , a convenient size . Fun quite satisfactory on a dedicated 20 amp 120 VAC circuit . 18,000 BTU will be either 240 VAC or 120 VAC ( I think ) . Larger will be 240 VAC .

God bless
Wyr

oil pan 4 · 06-07-17, 11:58 AM

I installed my overy sized split. A 2 ton for maybe 700 square feet. It works great.
We can use the stove during the day and not make the house hot.
I leave the unit off during the day turn it on when I get home it it cools the house down right away takes maybe 10 to 20 minutes.

jeff5may · 06-08-17, 08:50 AM

How you execute your heating and cooling system depends on the layout of your building. I am assuming you have abandoned the ground source idea, so the outdoor portion of an air-source rig is basically a choice between variable capacity, constant capacity, or both. How to size which portion of what zone or zones is the main factor here. Please elaborate on the layout of the building for better answers.

If you have a retail outlet type of venue, with one or two large "shopping" areas (FOH) and a storeroom/warehouse/receiving area, the demands are vastly desperate compared to an office complex with many smaller zones. With the info you have provided, there is no way to tell what will work on site for you. Not trying to be nosy, but if you run a gym, the zone and load handling is way different from a body shop or a bank.

WyrTwister · 06-08-17, 11:09 AM

If you run a gym ...

This brings up another mater , ceiling height . The greater the ceiling height , the more " interesting " it will be to design HVAC .

Air may tend to stratify . Especially hot hir in the heating season . Cool / cold air will tend to drop down to where the people are . Assuming the vents are located high , or at least a few feet above " head height " .

With a large room , I wonder if a ducted solution is better than a single ductless wall mounted solution . Ducted MS ceiling " cassets " are available , although my experience is only with wall mounted ductless units .

God bless
Wyr

God bless
Wyr

04-15-17, 08:31 PM	#15
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	We did the same thing with a rental property. The 14x70 aluminum box trailer had a "standard" sized gas furnace and a "premium" sized packaged air conditioning unit. After the furnace developed pilot problems, we swapped it for a "standard" double wide furnace. Everyone has been very happy with the extra heating capacity. I imagine it costs more to heat now than it did, but it's not a heat pump. If you are going to employ setback strategies, oversizing your HVAC unit will allow the quick recovery that this strategy dictates. Make sure to install a variable capacity system that can throttle back its output when the setpoint is reached. Last edited by jeff5may; 04-16-17 at 08:28 AM..

04-15-17, 07:15 AM	#12
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	The main reason for temperature setback arises from traditional gas furnaces. As you know, nearly every gas furnace in a reasonably sized single family home is oversized. The less gas burned, the lower the bill. When they operate, they blast out high-grade heated air. A quick burn causing a drastic temperature rise, followed by a not-so-quick coast to below setpoint, describes typical operation. Many older folks have been conditioned to accept this mode of operation as "ideal". My parents are two of them. We lived in Colorado, where during clear skies, when the sun went down, the temperature immediately dropped. The heat literally flew away to space all night. The thermostat on our home heating system had like a 7 or 8 degree deadband, so the furnace ran for a little longer when it kicked on. My father was a proponent of temp setback, and during those clear winter nights, the thermostat got set back like 10 or 20 degrees around dusk. I caught some sort of ear, nose, or throat disease about every year I was growing up, until I put a waterbed in my room. For some reason, all the other kids wanted to sleep in my room. It just felt more comfortable than the rest of the house. Besides the obvious health issues, temperature setback becomes less effective when you match your heating and cooling equipment to the home load. A "tiny" heat pump (or air conditioner) isn't able to quickly change the air temperature like a blast furnace (or blast freezer), so the short run period mentioned before goes away. The thermal mass and insulation/infiltration play a larger role in maintaining comfort levels, as well as a more responsive thermostat. Most modern systems include a thermostat with a 1 or 2 degree deadband and multiple stages of control. Yes, you still reduce the temperature gradient between indoors and outdoors with temperature setback, so any energy usage due to setback is still reduced while the unit sits idle. When the thermostat is returned to "normal", it takes a LONG time for the building to recover. The closer your HVAC system is sized to your actual heat load, the longer it takes the system to overcome the change in setpoint. On days where the temperature changes quickly (not uncommon in the southwest), the change may exceed the capacity of the system. The result is felt at the worst possible time, normally on some holiday weekend when you are home all day or have company. My parents always ran the fireplace in the evening, rather than not setting back the furnace. The moral of the story: if you are going to employ thermostat setback, have a backup source to fire up and prepare to shed or add clothes to maintain personal comfort. Or you can just sweat or shiver. Because oversizing your HVAC system is a waste.

04-15-17, 08:02 AM	#13
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Another phenomenon to consider, especially with air conditioning in summer, is thermal radiation and how it relates to comfort. Just cooling the air quickly is easy. When this happens, the only time you feel comfortable is when there is wind. The reason being is because all the "stuff" around you is still hot, and is in fact radiating its heat into you. Just having cool air present is not enough to maintain personal comfort, the mass inside the envelope has to be cool as well. As stated in the post before, it takes a LONG time to draw the extra heat out of the thermal mass inside the envelope of the structure. If the system is sized within a factor of less than 150% of your design heat load, there is more energy stored inside the envelope than can be quickly regulated by adding or removing heat with the HVAC system. If there is much infiltration, it quickly overcomes the limited capacity of the system. Many retail stores (think dollar store or mexican restaurant) suffer from this condition. During spring and fall, these venues are usually very cozy, since the system is not experiencing drastic outdoor weather changes. But this Easter weekend, here in Kentucky we are getting lots of sun and clear night skies. Just when the HVAC system has a chance to recover from the 90 degree day, the setpoint changes to above 75 degrees, and all that cool night air is not allowed to draw all the heat out of the hot product being restocked onto shelves. When the thermostat resets to 68 degrees in the morning, the system only has a couple of hours to move literally 100 tons of heat outdoors before the automatic sliding doors start moving. By noon, the HVAC system is ineffective. By 2 or 3 o'clock in the afternoon, the sliding doors have rendered the venue uncomfortable, and all you can do is pray for clouds without rain in them. On a positive note, the electric bill is 20% less than without setback, even counting the little fans all the cashiers are blowing in their general directions.

04-15-17, 08:24 AM	#14
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	That's exactly why I'm going over sized to be able to cool the house and everything inside down fast. Running the A/C all day when not home is just wasteful. If I was going so far oversized with an inverter to the point where it wouldn't work right I would have to put like a 2 ton in the bed room. We tried this on my friends house. The house flipper that had it before him put in a new barely large enough 2 ton heat pump. First he tried just leaving the 2 ton off all day then turning on when he got home, the 2 ton wouldn't turn off till 9 or 10 at night. He replaced the heat pump and air handler with a 4.5 ton. Leaving the 2 ton on all day versus turning the 4.5 ton on when some one comes home has cut his power consumption by at least 1/3 and up to 1/2. He said it paid for its self in 2 years. That was back in 2010 or 2011.

06-06-17, 09:48 PM	#16
WyrTwister Master EcoRenovator Join Date: Jun 2013 Location: USA Posts: 543 Thanks: 6 Thanked 44 Times in 38 Posts	As for as purchase cost and SEER ratings , of Mini-Splits , it has been about 2 years since I bought and installed one . So , I may be somewhat behind the curve . The MS's will be cheaper than WSHP's , to install . Maybe cheaper to purchase . MS's are available in amazing SEER ratings . And with hear ratings that go down to pretty low Outside Air Temperatures . Do you plan to contract out everything of do some / all via self install ? Let me ask this . Is your existing HVAC system still functional ? If so , start by installing one MS , of the highest energy rating you can afford . Maybe in a space that presently is poorly served . See how you like it . Remember , you do not have to do it all at once . And it will take the load off of equipment that may be just limping along . Or start out in an area that will allow you to completely obsolete one of the smaller existing HVAC units . As for as sizing is concerned , ductless MS;s do not suffer from duct losses . And the new inverter compressor drive technology will ramp op capacity / ramp down capacity , as needed . You can use multiple MS's to zone hour heat / cooling to fit your varying needs / schedule . Multiple units also give you redundancy . And if you can design the " system " so all or several of the units are identical , you might buy one extra unit ( indoor / outdoor unit ) for a standby / spare ? If it is critical to get a unit up and running , should one go down . As far as the indoor units , wall mounted units will be cheaper to purchase , but they make them that you can install in the attic , blowing directly down into the living space . Try one , you will like . Both of ours are 12,000 BTU , a convenient size . Fun quite satisfactory on a dedicated 20 amp 120 VAC circuit . 18,000 BTU will be either 240 VAC or 120 VAC ( I think ) . Larger will be 240 VAC . God bless Wyr

06-07-17, 11:58 AM	#17
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	I installed my overy sized split. A 2 ton for maybe 700 square feet. It works great. We can use the stove during the day and not make the house hot. I leave the unit off during the day turn it on when I get home it it cools the house down right away takes maybe 10 to 20 minutes.

06-08-17, 08:50 AM	#18
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	How you execute your heating and cooling system depends on the layout of your building. I am assuming you have abandoned the ground source idea, so the outdoor portion of an air-source rig is basically a choice between variable capacity, constant capacity, or both. How to size which portion of what zone or zones is the main factor here. Please elaborate on the layout of the building for better answers. If you have a retail outlet type of venue, with one or two large "shopping" areas (FOH) and a storeroom/warehouse/receiving area, the demands are vastly desperate compared to an office complex with many smaller zones. With the info you have provided, there is no way to tell what will work on site for you. Not trying to be nosy, but if you run a gym, the zone and load handling is way different from a body shop or a bank.

06-08-17, 11:09 AM	#19
WyrTwister Master EcoRenovator Join Date: Jun 2013 Location: USA Posts: 543 Thanks: 6 Thanked 44 Times in 38 Posts	If you run a gym ... This brings up another mater , ceiling height . The greater the ceiling height , the more " interesting " it will be to design HVAC . Air may tend to stratify . Especially hot hir in the heating season . Cool / cold air will tend to drop down to where the people are . Assuming the vents are located high , or at least a few feet above " head height " . With a large room , I wonder if a ducted solution is better than a single ductless wall mounted solution . Ducted MS ceiling " cassets " are available , although my experience is only with wall mounted ductless units . God bless Wyr God bless Wyr