Sunday, I ran the copper refrigerant lines in the crawlspace from the blowers to the outdoor unit. They are temporarily supported in place with a few hangers and some velcro straps. Once insulated, they will be permanently supported.
Monday, I spent Valentine's Day with my love.
Tuesday morning, I determined the motion sensor on the side of the house was bad. I spent almost an hour looking at lines and reading voltages and what not. I am slow. The rest of the day was spent helping install my parents' new dishwasher.
Wednesday, I replaced the motion sensor with a new one. I then made flares for the indoor refrigerant connections. It was too windy/dusty outside to work on the exterior flares.
Thursday, I connected the outside flares, pulled a vacuum on one set of blower lines, and cracked the service valve briefly for some soap & bubble checking with low pressures. No bubbles were spotted. This was an exciting day, as I learned the difference between standard hose fittings and low-loss/anti-blowback hose fittings. The latter are very, very handy.
Friday, I vacuumed the other blower lineset, also performed low pressure bubble checks and then fully opened both service valves. This was another fun day of driving back and forth from Milford to Dover, as I discovered the very limited space around the service valves on the Fujitsu required just the right combination of tiny fittings to adapt from a 5/16" to 1/4", and to bend 90 degrees from the unit housing for clearance. The wiring was completed, and the system connected. The instructions stated to wait 12 hours after power before testing.
Saturday morning, I tested the system heat. It was about mid-forties outside. The outside unit was very quiet. It very slowly ramped up its speed. The indoor blowers were also incredibly quiet.. Even full blast, the fans make little noise. They put out nice heat, too.
After an hour or less, I shut down the system to allow the lines to cool, so I could insulate them. As I was fumbling with some pipe insulation outside, I noticed a small bubble slowly form and pop at one of the low pressure flare nuts. I stooped down for a closer look, and watched another bubble slowly form and pop. Doh.
After some investigation of my documentation I determined it was possible I could perform a "pump down" or "recapture" to suck the refrigerant back out from the linesets into the outdoor unit. Then, I would be free to disassemble the flare and try again. If I haven't lost too much refrigerant - which I don't think I have - then it should still work fine without dealing with a recover/recycle operation. I don't have equipment for that, and would likely run a few hundred dollars to have a contractor perform for me. I don't even know if a supply house would sell me the R410A if I had a recovery unit, without a CFC card..
I realize now a nitrogen pressure test is critical to ensure a tight system before bringing the refrigerant into play. A $100 regulator isn't much of an investment, and I found a local supply house with nitrogen tanks.
So, I ordered online a nitrogen regular for $60, a leak detector for $40.. it should arrive sometime the middle of this week, and then I can check for leaks before I release the refrigerant again.
Once that's all done, I can check pressures and temperatures and compare to the spec sheets to ensure the charge is within acceptable range. The unit comes charged with enough refrigerant for a total line distance of 100ft. My units are roughly 40ft total, 60ft less than the max. The specs list a charge of about a quarter oz/ft, so with 60 x 0.25 = 15oz lost, it should still perform to spec. The total factory charge was 74oz, so that's about 20% lost. This is a guestimation of course, only testing will tell for sure.
In the mean time, I'll remake that one flare I know for sure is bad, when the weather looks good. I can run the pipe insulation as well. And finish the condensate piping. And the drain/waste/vent piping..
Showing posts with label hvac. Show all posts
Showing posts with label hvac. Show all posts
Saturday, February 19, 2011
Saturday, February 12, 2011
My poor blog..
It's been so neglected :\
A quick recap of the past week.
Thursday. The electrical inspector arrived for my rough-in. He looked around a bit, then shockingly noted I didn't make any splices in my boxes. I told him I didn't know I needed to. Live and learn.
He also noted at my aerial service entrance, the weatherhead was at 10ft from grade, which would cause the driploop to hang below that elevation, which is a code violation. He recommended I add a upward bend at the end of the conduit, to bring the weatherhead up about a foot, to place it in front of the soffit box.
Friday-Sunday. I purchased some necessary tools for making the box splices. I went through the house, each circuit at a time, splicing up neutral/ground/hot pigtails. It went a little slow at first, but near the end I'm now a pro splicer :P
The best tools to use I found were a pair of wire cutters to cut the romex to length, a pair of sheath strippers to quickly remove the romex sheath - and make sure they're bent nosed, or you won't be able to strip it inside the box, a pair of stripmasters to strip the individual THHN conductors, and a screwdriver with a hole at the end of the handle designed to turn wingnuts. Wingnuts are a brand of wirenuts with little wings on 'em, they're easier to turn, and the screwdriver really saves your fingers after putting on a ton of 'em. I also ordered an adapter which chucks into your drill to turn the wingnuts, but it still hasn't arrived yet - I'll try it on the next house!
Monday. I borrowed a large pipe cutter from Ed and cut off the existing weatherhead. I glued on a 90-sweep and then glued the head back on there. This was a real pain, with the conductors in place, it was difficult pulling the head and ell onto the existing conduit. Ah well, now the inspector can be satisfied that my drip loop won't hang a few inches below the magic ten foot line. I then scheduled another inspection.
Tuesday. Inspector eventually showed up, glanced at my splices, and left within 90 seconds of arrival. Before leaving, he told me I still get another inspection for free before they charge for additional inspections! He said I could use that for my final inspection. Mmm hmm. I'm sure, as an employee of a profit-oriented enterprise, he won't find anything that will need to be corrected at the final inspection. I then called the city to have the aerial line switched to the house.
Wednesday. A worker showed up early in the bitter cold to make the swap. We BSed a bit while he was working, and I made sure to tell him where the 10ft line was, and that the inspector was nitpicking and the bottom of the loop needed to be above that line. Of course, the neutral loop still ended up just at that line. It's a grounded conductor, so really there is no danger, but if the inspector wanted he could pitch a fit.
Once the power was switched, I jumped for joy. I was going to install a receptacle for power for my tools, but I realized all I had was a box of the old receptacles, which aren't Tamper Resistant. A few months ago, I had to apply for another electrical permit from the county, since my original permit from my temp pole install was over a year old. In that time the state adopted the newer version of the code, which requires all receptacles to be TR. It also requires additional AFCI breakers. All this crap costs money. I think I spent an additional $100 or so on this junk.
Thursday-Friday. I installed some receptacles, switches. Wired up a few circuits to the main panel. Now I have lights in the crawl and attic, and all the exterior lights wired up. I installed a few receptacles in the crawl and outside, and one in the laundry closet for my tools.
Now I'm going to finish plumbing, but I also want to get the HVAC system running. Those blowers can still give me some heat before I add the ductwork. It's all wired up, just needs to have the refigerant lines attached and pressurized. I have the copper and flaring tools.. Just need to run the lines, and then pull a vacuum on a nice, warm day. I'm also looking into getting a tank of nitrogen to run a nitrogen leak test, this would be a smart thing to do if not expensive. Otherwise, if there is a leak and I release the refrigerant into the lines, that will be a very expensive mistake to fix..
A quick recap of the past week.
Thursday. The electrical inspector arrived for my rough-in. He looked around a bit, then shockingly noted I didn't make any splices in my boxes. I told him I didn't know I needed to. Live and learn.
He also noted at my aerial service entrance, the weatherhead was at 10ft from grade, which would cause the driploop to hang below that elevation, which is a code violation. He recommended I add a upward bend at the end of the conduit, to bring the weatherhead up about a foot, to place it in front of the soffit box.
Friday-Sunday. I purchased some necessary tools for making the box splices. I went through the house, each circuit at a time, splicing up neutral/ground/hot pigtails. It went a little slow at first, but near the end I'm now a pro splicer :P
The best tools to use I found were a pair of wire cutters to cut the romex to length, a pair of sheath strippers to quickly remove the romex sheath - and make sure they're bent nosed, or you won't be able to strip it inside the box, a pair of stripmasters to strip the individual THHN conductors, and a screwdriver with a hole at the end of the handle designed to turn wingnuts. Wingnuts are a brand of wirenuts with little wings on 'em, they're easier to turn, and the screwdriver really saves your fingers after putting on a ton of 'em. I also ordered an adapter which chucks into your drill to turn the wingnuts, but it still hasn't arrived yet - I'll try it on the next house!
Monday. I borrowed a large pipe cutter from Ed and cut off the existing weatherhead. I glued on a 90-sweep and then glued the head back on there. This was a real pain, with the conductors in place, it was difficult pulling the head and ell onto the existing conduit. Ah well, now the inspector can be satisfied that my drip loop won't hang a few inches below the magic ten foot line. I then scheduled another inspection.
Tuesday. Inspector eventually showed up, glanced at my splices, and left within 90 seconds of arrival. Before leaving, he told me I still get another inspection for free before they charge for additional inspections! He said I could use that for my final inspection. Mmm hmm. I'm sure, as an employee of a profit-oriented enterprise, he won't find anything that will need to be corrected at the final inspection. I then called the city to have the aerial line switched to the house.
Wednesday. A worker showed up early in the bitter cold to make the swap. We BSed a bit while he was working, and I made sure to tell him where the 10ft line was, and that the inspector was nitpicking and the bottom of the loop needed to be above that line. Of course, the neutral loop still ended up just at that line. It's a grounded conductor, so really there is no danger, but if the inspector wanted he could pitch a fit.
Once the power was switched, I jumped for joy. I was going to install a receptacle for power for my tools, but I realized all I had was a box of the old receptacles, which aren't Tamper Resistant. A few months ago, I had to apply for another electrical permit from the county, since my original permit from my temp pole install was over a year old. In that time the state adopted the newer version of the code, which requires all receptacles to be TR. It also requires additional AFCI breakers. All this crap costs money. I think I spent an additional $100 or so on this junk.
Thursday-Friday. I installed some receptacles, switches. Wired up a few circuits to the main panel. Now I have lights in the crawl and attic, and all the exterior lights wired up. I installed a few receptacles in the crawl and outside, and one in the laundry closet for my tools.
Now I'm going to finish plumbing, but I also want to get the HVAC system running. Those blowers can still give me some heat before I add the ductwork. It's all wired up, just needs to have the refigerant lines attached and pressurized. I have the copper and flaring tools.. Just need to run the lines, and then pull a vacuum on a nice, warm day. I'm also looking into getting a tank of nitrogen to run a nitrogen leak test, this would be a smart thing to do if not expensive. Otherwise, if there is a leak and I release the refrigerant into the lines, that will be a very expensive mistake to fix..
Sunday, October 17, 2010
HVAC design
hello there. currently, i'm working on electrical, plumbing, and hvac systems. i'm going to focus on the hvac system in this post.
the system
i selected & purchased a system - it is a multizone split heatpump system made by fujitsu. it comes with one outdoor unit, model aou24rml1, and two indoor units, model aru12rml. this is considered a two-ton system. the indoor units are both blowers, and each comes with a wall-mounted remote.
the system can be installed as two separately controlled zones or two blowers in a single zone, controlled at one or two points. there are also cool accessories like wireless remotes that could be purchased, but i'm sticking with the basics ;)
the outdoor unit is smaller than a typical outdoor heatpump, and it employs a variable-speed compressor - 'inverter' type. this allows the system to operate at very high efficiencies during part load conditions, which makes it very efficient! good stuff.
the only downside is that this type of system is uncommon here, and if there are ever problems with the system it will be more problematic to fix, as the owner will likely need to find a service company that deals with fujitsu systems. my thinking is, hvac equipment efficiency is constantly going up, and by the time there is a problem with the system it will probably be obsolete and the service company will probably recommend replacement.
following this train of thought, i would like to make the existing system less problematic to upgrade/replace in the future. specifically, i'm focusing on designing the ductwork so it can be adapted to a more traditional single blower system. this should save the cost of conversion in the future.
however, i don't want to make any significant sacrifices in the efficiency of this system to meet that end. so, it requires some careful consideration in ductwork planning.
ductwork design
there are various methods of designing ductwork, from hand methods to computerized solutions. i've looked over these and considered the physics from the blower down through the registers, from efficiency & comfort considerations. i haven't found a clear method spelled out that satisfied me, but i have arrived at a process that i believe is optimal to follow - as it seems to optimize all considerations.
i did alot of reading and thinking to come up with this, and i'm providing it as a useful resource for anyone who might come across this post on the web. take it for what it's worth. it is summarized thus:
velocity = manuf(CFM, throw)
boot_size = area_to_diameter(CFM/velocity)
CFMs at each outlet are determined by heating/cooling needs (typ. a manual j calc) and the CFMs available by the blower. the number of outlets in each room are adjustable to arrive at a typical-range CFM at the register to give good air distribution.
throw at each outlet is dependent on the room dimensions and the register location (read up on ADPI for more details on this.) for typical baseboard registers with spread vanes, throw should be 0.7 x distance to far wall (gives ft/s.)
velocity at each outlet is found by referencing manufacturer data sheets of the selected register/grille. it will depend on a combination of CFM and desired throw.
the outlet/boot beneath the floor register/grille is sized by dividing CFM by the velocity. this gives the cross-sectional area of your outlet, and using a = pi x r^2, we find diameter = 2 x square_root(area/pi).
---
all supply and return branches run from the blower to conditioned space. the pressure at the blower is the same for all branches because it's in the same place (obviously) and the pressure in conditioned space should be the same (so use passive ducts between rooms if necessary.) thus, we can see why the total pressure drop of each branch will be equal.
the total pressure drop of a branch is the total equivalent length (TEL) times the friction rate (FR). TEL x FR of each branch should be equal. if they aren't, the delivered CFMs will deviate from that expected.
TEL of each branch is a sum of duct lengths and the equivalent length of all fittings. equivalent lengths can be found in data tables. FR is dependent on CFMs, duct diameter, and duct smoothness.
a 'ductulator' program is used to select an appropriate diameter for given CFMs and desired FR. if some section of ductwork is a size not consistent with your desired FR, you can calculate the pressure drop of that section only with it's TEL x actual FR, and add that to the TEL x FR of the rest of the ductwork.
for even more accuracy, instead of using equivalent lengths of fittings, the friction loss at a fitting can be calculated using a coefficient in conjunction with the velocity pressure (which is dependent on velocity at the fitting) - and these coefficients are found in data tables for the fittings. such a method would add the fitting pressure loss to ductwork length x FR
And so you can now size all of the ductwork.
the system
i selected & purchased a system - it is a multizone split heatpump system made by fujitsu. it comes with one outdoor unit, model aou24rml1, and two indoor units, model aru12rml. this is considered a two-ton system. the indoor units are both blowers, and each comes with a wall-mounted remote.
the system can be installed as two separately controlled zones or two blowers in a single zone, controlled at one or two points. there are also cool accessories like wireless remotes that could be purchased, but i'm sticking with the basics ;)
the outdoor unit is smaller than a typical outdoor heatpump, and it employs a variable-speed compressor - 'inverter' type. this allows the system to operate at very high efficiencies during part load conditions, which makes it very efficient! good stuff.
the only downside is that this type of system is uncommon here, and if there are ever problems with the system it will be more problematic to fix, as the owner will likely need to find a service company that deals with fujitsu systems. my thinking is, hvac equipment efficiency is constantly going up, and by the time there is a problem with the system it will probably be obsolete and the service company will probably recommend replacement.
following this train of thought, i would like to make the existing system less problematic to upgrade/replace in the future. specifically, i'm focusing on designing the ductwork so it can be adapted to a more traditional single blower system. this should save the cost of conversion in the future.
however, i don't want to make any significant sacrifices in the efficiency of this system to meet that end. so, it requires some careful consideration in ductwork planning.
ductwork design
there are various methods of designing ductwork, from hand methods to computerized solutions. i've looked over these and considered the physics from the blower down through the registers, from efficiency & comfort considerations. i haven't found a clear method spelled out that satisfied me, but i have arrived at a process that i believe is optimal to follow - as it seems to optimize all considerations.
i did alot of reading and thinking to come up with this, and i'm providing it as a useful resource for anyone who might come across this post on the web. take it for what it's worth. it is summarized thus:
velocity = manuf(CFM, throw)
boot_size = area_to_diameter(CFM/velocity)
CFMs at each outlet are determined by heating/cooling needs (typ. a manual j calc) and the CFMs available by the blower. the number of outlets in each room are adjustable to arrive at a typical-range CFM at the register to give good air distribution.
throw at each outlet is dependent on the room dimensions and the register location (read up on ADPI for more details on this.) for typical baseboard registers with spread vanes, throw should be 0.7 x distance to far wall (gives ft/s.)
velocity at each outlet is found by referencing manufacturer data sheets of the selected register/grille. it will depend on a combination of CFM and desired throw.
the outlet/boot beneath the floor register/grille is sized by dividing CFM by the velocity. this gives the cross-sectional area of your outlet, and using a = pi x r^2, we find diameter = 2 x square_root(area/pi).
---
all supply and return branches run from the blower to conditioned space. the pressure at the blower is the same for all branches because it's in the same place (obviously) and the pressure in conditioned space should be the same (so use passive ducts between rooms if necessary.) thus, we can see why the total pressure drop of each branch will be equal.
the total pressure drop of a branch is the total equivalent length (TEL) times the friction rate (FR). TEL x FR of each branch should be equal. if they aren't, the delivered CFMs will deviate from that expected.
TEL of each branch is a sum of duct lengths and the equivalent length of all fittings. equivalent lengths can be found in data tables. FR is dependent on CFMs, duct diameter, and duct smoothness.
a 'ductulator' program is used to select an appropriate diameter for given CFMs and desired FR. if some section of ductwork is a size not consistent with your desired FR, you can calculate the pressure drop of that section only with it's TEL x actual FR, and add that to the TEL x FR of the rest of the ductwork.
for even more accuracy, instead of using equivalent lengths of fittings, the friction loss at a fitting can be calculated using a coefficient in conjunction with the velocity pressure (which is dependent on velocity at the fitting) - and these coefficients are found in data tables for the fittings. such a method would add the fitting pressure loss to ductwork length x FR
And so you can now size all of the ductwork.
Saturday, May 1, 2010
the indoor unit
a pic of the indoor air handler of the samsung unit i'm looking at currently:
it's big, like 3 1/2 feet wide.. and 8" tall
it's big, like 3 1/2 feet wide.. and 8" tall
Friday, April 30, 2010
economics of heat
let's discuss the cost of home heating briefly. in a recent discussion, someone told me it would be cheaper to use a gas furnace to heat the house than a heat pump. a quick google gave me a page comparing the options like so:
propane (95,000 BTU/gal) @ $2.83/gal = $29.79/million btu
oil (140,000 BTU/gal) @ $3.11/gal = $22.21/million btu
elect (3410 BTU/kwhr) @ $0.14/kwhr = $41.06/million btu
nat gas @ $15.15/million btu
the author also made note that nat.gas is more locally produced energy, most propane comes from processing nat.gas (which makes it more expensive), and oil pricing is volatile.
i adjusted the prices to the DOE outlooks for 2011. from this comparison, nat gas appears to be the least expensive. however, the efficiency rating of the furnace will reduce the number of BTUs used to heat your home. the other BTUs go out the flue pipe...
except for heat pumps, which don't have flue pipes. in fact, the efficiency ratings of the heat pumps i'm looking at actually *increase* the number of BTUs used to heat the home. common rating indicators used are HSPF or heating COP.
COP is a direct ratio of energy consumed by heat pump to energy moved into the house by the heat pump. A COP of 3, for instance, means a heat pump would consume 2kW to meet a 6kW load. The COP of a heat pump varies depending on the conditions (indoor & outdoor coil temperatures.)
HSPF is a ratio of energy consumed to energy moved, but over an entire simulated heating season (including the various indoor/outdoor conditions.) HSPF varies with geographic location, but most equipment specifications are listed for 'region IV'..
You can convert HSPF to an average COP value like so:
avg COP = HSPF / 3.413
The Fujitsu i mentioned earlier had an HSPF of 8.6. avg COP = 8.6/3.413 = 2.52
now we can take that average COP and multiply it by the BTUs per kwh listed for electricity in the energy rates i listed at the beginning of this blog..
elect (3410 x 2.52 BTU/kwhr) @ $0.14/kwhr = $16.29/million btu
this is just slightly more expensive than natural gas, with $15.15/million assuming a 100% efficiency furnace. the best ones are rated 95+%.. at 95%, it's $15.95/million.
if you recall, there were other inverter systems i considered selecting. one i've had my eye on for a while is seemingly well oversized for my needs. it is a samsung unit, UH105CAV + DH105CAV. one zone, one interior unit with a 'medium static pressure' blower. with an HSPF of 9.3...
9.3/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $15.05/million
this unit will be cheaper than a 100% afue natural gas furnace to operate.
but wait, there's more..
one of the first units i was considering was a sanyo, the 26UHW72R, one zone with a single indoor blower that can handle medium static pressures also. this unit has an impressive 9.7 HSPF rating. *however, i just discovered the ahri listing for this combination is 9.0 HSPF... :\
9.7/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $14.43/million
sweet. however, the sanyo costs $400 more than the samsung. the samsung will be able to heat the house at lower outdoor conditions (perhaps 5F lower.) the sanyo is more closely sized to the house load, which means the predicted efficiency of the sanyo is likely closer to reality than the samsung. plus the sanyo would probably do a better job at reducing indoor humidity during the summer..
ah, decisions, decisions..
propane (95,000 BTU/gal) @ $2.83/gal = $29.79/million btu
oil (140,000 BTU/gal) @ $3.11/gal = $22.21/million btu
elect (3410 BTU/kwhr) @ $0.14/kwhr = $41.06/million btu
nat gas @ $15.15/million btu
the author also made note that nat.gas is more locally produced energy, most propane comes from processing nat.gas (which makes it more expensive), and oil pricing is volatile.
i adjusted the prices to the DOE outlooks for 2011. from this comparison, nat gas appears to be the least expensive. however, the efficiency rating of the furnace will reduce the number of BTUs used to heat your home. the other BTUs go out the flue pipe...
except for heat pumps, which don't have flue pipes. in fact, the efficiency ratings of the heat pumps i'm looking at actually *increase* the number of BTUs used to heat the home. common rating indicators used are HSPF or heating COP.
COP is a direct ratio of energy consumed by heat pump to energy moved into the house by the heat pump. A COP of 3, for instance, means a heat pump would consume 2kW to meet a 6kW load. The COP of a heat pump varies depending on the conditions (indoor & outdoor coil temperatures.)
HSPF is a ratio of energy consumed to energy moved, but over an entire simulated heating season (including the various indoor/outdoor conditions.) HSPF varies with geographic location, but most equipment specifications are listed for 'region IV'..
You can convert HSPF to an average COP value like so:
avg COP = HSPF / 3.413
The Fujitsu i mentioned earlier had an HSPF of 8.6. avg COP = 8.6/3.413 = 2.52
now we can take that average COP and multiply it by the BTUs per kwh listed for electricity in the energy rates i listed at the beginning of this blog..
elect (3410 x 2.52 BTU/kwhr) @ $0.14/kwhr = $16.29/million btu
this is just slightly more expensive than natural gas, with $15.15/million assuming a 100% efficiency furnace. the best ones are rated 95+%.. at 95%, it's $15.95/million.
if you recall, there were other inverter systems i considered selecting. one i've had my eye on for a while is seemingly well oversized for my needs. it is a samsung unit, UH105CAV + DH105CAV. one zone, one interior unit with a 'medium static pressure' blower. with an HSPF of 9.3...
9.3/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $15.05/million
this unit will be cheaper than a 100% afue natural gas furnace to operate.
but wait, there's more..
one of the first units i was considering was a sanyo, the 26UHW72R, one zone with a single indoor blower that can handle medium static pressures also. this unit has an impressive 9.7 HSPF rating. *however, i just discovered the ahri listing for this combination is 9.0 HSPF... :\
9.7/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $14.43/million
sweet. however, the sanyo costs $400 more than the samsung. the samsung will be able to heat the house at lower outdoor conditions (perhaps 5F lower.) the sanyo is more closely sized to the house load, which means the predicted efficiency of the sanyo is likely closer to reality than the samsung. plus the sanyo would probably do a better job at reducing indoor humidity during the summer..
ah, decisions, decisions..
Tuesday, April 27, 2010
more mini-split-ness
more system research changed a few small details of the systems i listed previously..
the low-heat (17F) capacity of the fujitsu system i listed was incorrect. that figure was the cooling capacity at 17F (don't ask me why they list the cooling capacity of the system at 17F..) heating capacity of the 24rmlq-c is actually 25.4kbtu/h, which is more than i need.
there is a smaller fujitsu system available, the 18rmlq-c. this system includes a 24rml1 outdoor unit, and two aru9rml indoor blowers. i am over 95% certain this is the system i will be ordering. specs:
cooling capacity: 11-22.6kbtu/h
heating capacity: 11-26kbtu/h
EER:10.6 SEER:15 HSPF:8.6 COP(heating):3
low-heat (17F) capacity: 21kbtu/h
price: $2500
the heating & cooling capacity ranges listed on the spec sheet are what is available from the system at a specific indoor & outdoor condition.
cooling conditions: 80F.DB/67F.WB indoor, 95F.DB/75F.WB outdoor
heating conditions: 70F.DB/60F.WB indoor, 47F.DB/43F.WB outdoor
the fujitsu tech manual also provides a table listing system performance under various combinations of indoor & outdoor temperatures. total capacity and power input of the system for each combination is provided. a look at the cooling table should provide insight into the system's dehumidification potential during the cooling season:
look at the 80F indoor column and the 95F outdoor row.. the TC here is 22.6kbtu/h, same as the max capacity listed in the main spec table. milder days of say 77F outdoor.. with an indoor temp of 70/75F.. TC is about 20kbtu/h. this is the maximum TC.. the spec sheet range of 11-22.6 could be roughly scaled to say 10-20kbtuh.. perhaps a minimum of a little below 10kbtu/h.
this table doesn't specify the outdoor wet bulb. if i assume the same WB for all outdoor conditions, say 77F.DB/75F.WB, and plug that into rhvac along with a 70F.DB/60F.WB indoor condition, then rhvac gives me a cooling load of 9k-9.5k (depending on if the house is extremely air tight or average air tight).
so if my assumption of outdoor wet bulb is correct, then this system should be able to very nearly match the load during mild summer conditions.
ok, i am going to move on with the assumption of selecting this system for purchase. next, i need to determine all of the equipment and accessories i will need for installation.
the low-heat (17F) capacity of the fujitsu system i listed was incorrect. that figure was the cooling capacity at 17F (don't ask me why they list the cooling capacity of the system at 17F..) heating capacity of the 24rmlq-c is actually 25.4kbtu/h, which is more than i need.
there is a smaller fujitsu system available, the 18rmlq-c. this system includes a 24rml1 outdoor unit, and two aru9rml indoor blowers. i am over 95% certain this is the system i will be ordering. specs:
cooling capacity: 11-22.6kbtu/h
heating capacity: 11-26kbtu/h
EER:10.6 SEER:15 HSPF:8.6 COP(heating):3
low-heat (17F) capacity: 21kbtu/h
price: $2500
the heating & cooling capacity ranges listed on the spec sheet are what is available from the system at a specific indoor & outdoor condition.
cooling conditions: 80F.DB/67F.WB indoor, 95F.DB/75F.WB outdoor
heating conditions: 70F.DB/60F.WB indoor, 47F.DB/43F.WB outdoor
the fujitsu tech manual also provides a table listing system performance under various combinations of indoor & outdoor temperatures. total capacity and power input of the system for each combination is provided. a look at the cooling table should provide insight into the system's dehumidification potential during the cooling season:
look at the 80F indoor column and the 95F outdoor row.. the TC here is 22.6kbtu/h, same as the max capacity listed in the main spec table. milder days of say 77F outdoor.. with an indoor temp of 70/75F.. TC is about 20kbtu/h. this is the maximum TC.. the spec sheet range of 11-22.6 could be roughly scaled to say 10-20kbtuh.. perhaps a minimum of a little below 10kbtu/h.
this table doesn't specify the outdoor wet bulb. if i assume the same WB for all outdoor conditions, say 77F.DB/75F.WB, and plug that into rhvac along with a 70F.DB/60F.WB indoor condition, then rhvac gives me a cooling load of 9k-9.5k (depending on if the house is extremely air tight or average air tight).
so if my assumption of outdoor wet bulb is correct, then this system should be able to very nearly match the load during mild summer conditions.
ok, i am going to move on with the assumption of selecting this system for purchase. next, i need to determine all of the equipment and accessories i will need for installation.
Sunday, April 25, 2010
hvac system selection
lately i've been giving mini-split hvac systems some serious attention. i originally assumed i would be installing a traditional heat pump system, with the air handling unit (ahu) located in the crawlspace. however, the maintenance of indoor air conditions is a rather complex operation - and i believe some available mini-split systems do a much better job of fulfilling this role well.
the main trigger to this change in equipment plans was a figure in the ashrae 2008 hvac systems and equipment manual:
it's quite apparent that control of interior humidity is essential to healthy indoor conditions. my simulations with the ornl wufi building envelope simulator about a year ago gave me familiarity with expected indoor humidity variations throughout the year in this local climate, in buildings with and without humidity control (and with or without a vapor barrier in the wall.)
i know from my readings that proper sizing of hvac equipment is stressed. oversizing is common, and this leads to the system turning on and shutting off repeatedly for very short periods. this wastes energy, puts wear on the mechanical components, and it leads to high humidity levels. because the system is usually sitting idle when it's oversized, the coil temperature warms closer to indoor temperature.
a properly sized system is usually on, which keeps the coil cold. interior air condenses on the coil and is carried away on the condensate drain. this process dehumidifies the air. from the figure shown earlier, we know there is a sweet spot for desired humidity. not too dry, not too wet. the system's ability to dehumidify depends on how long that coil is running cool.
when a system is sized, it's capacity is matched to an extremely high load condition, which is a figure dependent on geographical location, and is derived from statistical observation of local weather patterns. even a properly sized system will have a capacity greater than the given load on most days throughout the year. the system capacity is only met on those very hot or very cold days. this means on most days it's still not running optimally, but of course it's better than being drastically oversized.
many mini-split systems on the market today employ what's called an inverter compressor. this is a dc-powered compressor, and its input voltage can be variably adjusted (with an inverter) to control the rate at which the compressor runs. changes in compressor speed equate to changes in refrigerant flow between indoor and outdoor units, and ultimately to changes in rate of heat exchange for a given air speed over the coil.
this, in a sense, changes the capacity of the heat pump. the indoor coil and outdoor heat exchanger still have the same surface area exposed to local air, but the amount of heat available for exchange on those surfaces is different. this allows an intelligent controller to optimize conditions for dehumidification, and allows the system to be ramped down enough to keep it on constantly without the on/off/on/off cycling of traditional systems.
the powerful dehumidification abilities of variable compressor speed is what really attracts me to these minisplits. it doesn't hurt that they offer high EER/SEER performance for their cost, either. a few traditional split systems are on the market with variable compressor ability, but they are very expensive and hard to come by.
i scoured the internet and made a list of potential systems to purchase. most minisplits come with a wall mount indoor unit, as these are easy to install and mini-splits are usually selected for retrofit applications because of this. however, there are also indoor units that are like miniature indoor air handlers, with a blower and coil, and they are connected to ductwork. i plan to use these as it allows me to direct fresh conditioned air directly to everywhere i want it, and it presents in a traditional fashion to people (potential home buyers) as good old registers and diffusers.
i also looked for units that would closely match the load requirements of vinnie. i ran the house specs through a load sizing program, rhvac, and it gave me back precise load values for all parts of the house. total summer cooling load is 11,634 kbtu/h and total winter heating load is 16,566 kbtu/h. all system specs also list the heating capacity at low temperatures (17F) and the winter figure produced by rhvac is for 15F outdoor conditions. so i ensured the systems can meet this load at 15F. this requirement excluded a few otherwise excellent contenders..
the short list of favorites remaining:
lg lmu245hv + lmdn095hv (x2) - 10.8 EER, 8.1 HSPF, 10.8k min cool, 21.1k? low heat, $3100
fujitsu 24rmlq-c ; 24rml1 + aru12rml (x2) - 9.5 EER, 8.6 HSPF, 11k min cool, 16.6k low heat, $2500
sanyo 26uhw72r ; ch2672r + uh2672r - 9.1 EER, 9.7 HSPF, 9.5k min cool, 17.1k low heat, $3040
i couldn't retrieve explicit low heat capacity for the lg, so i may have to upgrade the two blower units from 9k to 12k units. prices are what i dug up with minimal effort through google. the fujitsu may find itself the winner. i listed minimum cooling capacities because the lower numbered systems may do a better job dehumidifying on mild but humid days. the high EER of the lg is attractive, as this could correspond to much lower bills.. almost 2 points higher than the sanyo.
however EER is cooling performance, whereas HSPF is heating performance. look at the sanyo HSPF, blows the other two away. i expect yearly heating costs to far exceed yearly cooling costs. past simulations with resfen have indicated about seven times as much energy required for heating than cooling, annually (3680kWh vs 554kWh). that's 88% of annual energy is heating. i suppose i didn't need to list the EER..
the sanyo is a $640 premium over the fujitsu. the 9.7 HSPF is 1.1 greater than 8.6, 1.1/8.6 = 12.8% better. 640 * 1/.128 = $5,000. so ~13% savings in heating would pay off the $640 cost after $5k had been spent on heating bills.. guestimate $60/mo average bill..$720/yr.. that's like 7 years to pay for itself. ah, might as well save the $640 now.. fujitsu..
decisions, decisions..
the main trigger to this change in equipment plans was a figure in the ashrae 2008 hvac systems and equipment manual:
it's quite apparent that control of interior humidity is essential to healthy indoor conditions. my simulations with the ornl wufi building envelope simulator about a year ago gave me familiarity with expected indoor humidity variations throughout the year in this local climate, in buildings with and without humidity control (and with or without a vapor barrier in the wall.)
i know from my readings that proper sizing of hvac equipment is stressed. oversizing is common, and this leads to the system turning on and shutting off repeatedly for very short periods. this wastes energy, puts wear on the mechanical components, and it leads to high humidity levels. because the system is usually sitting idle when it's oversized, the coil temperature warms closer to indoor temperature.
a properly sized system is usually on, which keeps the coil cold. interior air condenses on the coil and is carried away on the condensate drain. this process dehumidifies the air. from the figure shown earlier, we know there is a sweet spot for desired humidity. not too dry, not too wet. the system's ability to dehumidify depends on how long that coil is running cool.
when a system is sized, it's capacity is matched to an extremely high load condition, which is a figure dependent on geographical location, and is derived from statistical observation of local weather patterns. even a properly sized system will have a capacity greater than the given load on most days throughout the year. the system capacity is only met on those very hot or very cold days. this means on most days it's still not running optimally, but of course it's better than being drastically oversized.
many mini-split systems on the market today employ what's called an inverter compressor. this is a dc-powered compressor, and its input voltage can be variably adjusted (with an inverter) to control the rate at which the compressor runs. changes in compressor speed equate to changes in refrigerant flow between indoor and outdoor units, and ultimately to changes in rate of heat exchange for a given air speed over the coil.
this, in a sense, changes the capacity of the heat pump. the indoor coil and outdoor heat exchanger still have the same surface area exposed to local air, but the amount of heat available for exchange on those surfaces is different. this allows an intelligent controller to optimize conditions for dehumidification, and allows the system to be ramped down enough to keep it on constantly without the on/off/on/off cycling of traditional systems.
the powerful dehumidification abilities of variable compressor speed is what really attracts me to these minisplits. it doesn't hurt that they offer high EER/SEER performance for their cost, either. a few traditional split systems are on the market with variable compressor ability, but they are very expensive and hard to come by.
i scoured the internet and made a list of potential systems to purchase. most minisplits come with a wall mount indoor unit, as these are easy to install and mini-splits are usually selected for retrofit applications because of this. however, there are also indoor units that are like miniature indoor air handlers, with a blower and coil, and they are connected to ductwork. i plan to use these as it allows me to direct fresh conditioned air directly to everywhere i want it, and it presents in a traditional fashion to people (potential home buyers) as good old registers and diffusers.
i also looked for units that would closely match the load requirements of vinnie. i ran the house specs through a load sizing program, rhvac, and it gave me back precise load values for all parts of the house. total summer cooling load is 11,634 kbtu/h and total winter heating load is 16,566 kbtu/h. all system specs also list the heating capacity at low temperatures (17F) and the winter figure produced by rhvac is for 15F outdoor conditions. so i ensured the systems can meet this load at 15F. this requirement excluded a few otherwise excellent contenders..
the short list of favorites remaining:
lg lmu245hv + lmdn095hv (x2) - 10.8 EER, 8.1 HSPF, 10.8k min cool, 21.1k? low heat, $3100
fujitsu 24rmlq-c ; 24rml1 + aru12rml (x2) - 9.5 EER, 8.6 HSPF, 11k min cool, 16.6k low heat, $2500
sanyo 26uhw72r ; ch2672r + uh2672r - 9.1 EER, 9.7 HSPF, 9.5k min cool, 17.1k low heat, $3040
i couldn't retrieve explicit low heat capacity for the lg, so i may have to upgrade the two blower units from 9k to 12k units. prices are what i dug up with minimal effort through google. the fujitsu may find itself the winner. i listed minimum cooling capacities because the lower numbered systems may do a better job dehumidifying on mild but humid days. the high EER of the lg is attractive, as this could correspond to much lower bills.. almost 2 points higher than the sanyo.
however EER is cooling performance, whereas HSPF is heating performance. look at the sanyo HSPF, blows the other two away. i expect yearly heating costs to far exceed yearly cooling costs. past simulations with resfen have indicated about seven times as much energy required for heating than cooling, annually (3680kWh vs 554kWh). that's 88% of annual energy is heating. i suppose i didn't need to list the EER..
the sanyo is a $640 premium over the fujitsu. the 9.7 HSPF is 1.1 greater than 8.6, 1.1/8.6 = 12.8% better. 640 * 1/.128 = $5,000. so ~13% savings in heating would pay off the $640 cost after $5k had been spent on heating bills.. guestimate $60/mo average bill..$720/yr.. that's like 7 years to pay for itself. ah, might as well save the $640 now.. fujitsu..
decisions, decisions..
Subscribe to:
Posts (Atom)