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..
Friday, April 30, 2010
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..
Monday, April 12, 2010
foundation parging
i'm currently trying to get the lath to lay flat. you can see my dilemma here:
 |
| From vinnie pics by mike |
revised moola
i also plotted a running sum of my expenditures over time.
according to the red linear trendline, one year from now i'll have spent just under $45k. that's assuming i continue spending money at a linear rate, which is a silly assumption. just interesting to see, i suppose.
Saturday, April 3, 2010
foundation wall covering
sorry i have no pics; i keep forgetting the camera.
the past few days i've dug out around the foundation to expose 3' of foundation wall. this is enough for the hardware cloth to be attached. i still need to do a little more digging, especially b/c i may need more clearance to attach screws at lower parts of the wall, to hold the mesh to the foam.
i've got 6 50lb bags of surface bonding cement on-hand, along with a dozen quarts of acrylic admix. this is sufficient for 300sf of coverage at 1/8" thickness. hopefully i wont need more, but i'm prepared to go out and buy more if needed. it's not terribly expensive. about $70 each for the cement and the admix.
tomorrow is easter, so im not sure if i'll venture out there for work on a holiday. i'm not looking forward to trying to get the mesh into place by myself; i'm sure it will get dirt all over it while struggling with the long lengths of it. i suppose i'll attach it into position and then spray it down with the hose.. this will make a muddy mess and has the potential to delay the stucco. hopefully i just push through and get 'er done.
this needs to get done and over with - i don't want a moat around my house after the next rain.
obviously, in the future, i should stucco the foundation before backfilling. all this excavation and dealing with dirt is extra work and takes alot of time. my priority then was getting the roof on, but in retrospect it only cost me time and labor later on.
yesterday, i also got a foam can and sprayed the gaps in the gable wall sheathing just below the ridge, as wasps were using it as a door. i also filled in gaps in the sill plate and band joist while the can was being used.
i purchased a roll of fiberglass window screen, 3' x 25', for about 20 bux. i cut this into small pieces and stapled them up in the attic, covering the lower air vents. i used short galv staples in the staple gun, this worked ok but drove through the screen a few times. i should try out a simple T50 spring actuated stapler. why do pneumatic staplers seem to have such poor control/consistency?
anyway, i used standard window screen instead of a 1/2" hardware cloth, as it would reject more, smaller, insects. the lower air vents are well over-sized in relation to the upper ridge vent, and the reduction in cross section from the finer mesh doesn't hinder the roof ventilation system. fyi, i calc'd an approx 65% ventilation rate with the screen in place, which is with an 18x16 mesh.
the past few days i've dug out around the foundation to expose 3' of foundation wall. this is enough for the hardware cloth to be attached. i still need to do a little more digging, especially b/c i may need more clearance to attach screws at lower parts of the wall, to hold the mesh to the foam.
i've got 6 50lb bags of surface bonding cement on-hand, along with a dozen quarts of acrylic admix. this is sufficient for 300sf of coverage at 1/8" thickness. hopefully i wont need more, but i'm prepared to go out and buy more if needed. it's not terribly expensive. about $70 each for the cement and the admix.
tomorrow is easter, so im not sure if i'll venture out there for work on a holiday. i'm not looking forward to trying to get the mesh into place by myself; i'm sure it will get dirt all over it while struggling with the long lengths of it. i suppose i'll attach it into position and then spray it down with the hose.. this will make a muddy mess and has the potential to delay the stucco. hopefully i just push through and get 'er done.
this needs to get done and over with - i don't want a moat around my house after the next rain.
obviously, in the future, i should stucco the foundation before backfilling. all this excavation and dealing with dirt is extra work and takes alot of time. my priority then was getting the roof on, but in retrospect it only cost me time and labor later on.
yesterday, i also got a foam can and sprayed the gaps in the gable wall sheathing just below the ridge, as wasps were using it as a door. i also filled in gaps in the sill plate and band joist while the can was being used.
i purchased a roll of fiberglass window screen, 3' x 25', for about 20 bux. i cut this into small pieces and stapled them up in the attic, covering the lower air vents. i used short galv staples in the staple gun, this worked ok but drove through the screen a few times. i should try out a simple T50 spring actuated stapler. why do pneumatic staplers seem to have such poor control/consistency?
anyway, i used standard window screen instead of a 1/2" hardware cloth, as it would reject more, smaller, insects. the lower air vents are well over-sized in relation to the upper ridge vent, and the reduction in cross section from the finer mesh doesn't hinder the roof ventilation system. fyi, i calc'd an approx 65% ventilation rate with the screen in place, which is with an 18x16 mesh.
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