Does a climatemaster 3 ton also offer 2 stage if I can get it down further? And whats the seconds stage rating? Thanks

Posted By drlebel on 13 Nov 2012 06:05 PM
Okay by beefing up the foundation insulation and reducing inside temp from 74 to 69(didnt notice how high it was before and that is usually what I keep mine at during day and 66 at night) I can reduce BTU loss to 42,000. Gain is 36,000. Could I go with a 3.5 ton climate master at this range? Thanks

You might strongly consider going with 3-tons.   A shortfall of 6000BTU/hr is less than 2kw.  How many sleeping humans did you anticipate (and are they include in your calc at 250BTU/person?)  Most calculation tools overshoot reality by at least 10% too.

Calculate the heat load at 65F, and it would probably hit 3 tons (or less) and the odds that you'd ACTUALLY see 65F at the 99% condition with a full 3 tons of output are low even without engaging heating strips.  The 99% condition (or lower) occurs only for 1% of the binned hours of the heating season-  usually hours when most people are in bed anyway, where dropping a degree or three below 69F would not be a disaster.  The heat load begins to drop quickly & dramatically at dawn on design day, and can easily fall to half the peak load by noon.

In a higher-R & higher-mass houses the degrees/hour time-constant drop of the house is also much longer than in low-mass code min houses, which lowers but stretches the peak loads, and the 99% condition is usually low persistence, a few hours at most.  Heat load calculation tools usually don't model mass effects & time constants very well, but a shortfall of 6000 BTU/hr (if it's even truly that high) for 3 hours not usually a comfort problem in a higher-R / higher-mass house.

Posted By Dana1 on 14 Nov 2012 11:11 AM

Posted By drlebel on 13 Nov 2012 06:05 PM
Okay by beefing up the foundation insulation and reducing inside temp from 74 to 69(didnt notice how high it was before and that is usually what I keep mine at during day and 66 at night) I can reduce BTU loss to 42,000. Gain is 36,000. Could I go with a 3.5 ton climate master at this range? Thanks

You might strongly consider going with 3-tons.   A shortfall of 6000BTU/hr is less than 2kw.  How many sleeping humans did you anticipate (and are they include in your calc at 250BTU/person?)  Most calculation tools overshoot reality by at least 10% too.

Calculate the heat load at 65F, and it would probably hit 3 tons (or less) and the odds that you'd ACTUALLY see 65F at the 99% condition with a full 3 tons of output are low even without engaging heating strips.  The 99% condition (or lower) occurs only for 1% of the binned hours of the heating season-  usually hours when most people are in bed anyway, where dropping a degree or three below 69F would not be a disaster.  The heat load begins to drop quickly & dramatically at dawn on design day, and can easily fall to half the peak load by noon.

In a higher-R & higher-mass houses the degrees/hour time-constant drop of the house is also much longer than in low-mass code min houses, which lowers but stretches the peak loads, and the 99% condition is usually low persistence, a few hours at most.  Heat load calculation tools usually don't model mass effects & time constants very well, but a shortfall of 6000 BTU/hr (if it's even truly that high) for 3 hours not usually a comfort problem in a higher-R / higher-mass house.

But you are forgetting its not just a 6,000 BTU shortfall, its closer to 12,000-17,000 BTU's. Most closed loop systems at full capacity and a 30-40 degree EWT are going to be derated by about 6,000-11,000 BTU from the "size" the manufacture claims(WaterFurnace shows 30,000 BTU's on a two stage 3 ton unit at a 40 degree EWT and 25,500 BTUS on a two stage 3 ton with 30 degree EWT during a time when the homeowner needs 42,000 to be comfortable). My WaterFurnace pricing also puts me about $600 more for a 4 ton vs a 3 ton system plus any additional ductwork that would be needed for the additional airflow and loop shouldn't need to be to much bigger but that will be ground dependant.
To me it comes down to would you rather spend the extra $1,000 for a 4 ton with extra ductwork and ground loop and ensure no backup heat used and being comfortable all the time or saving the $1,000 and paying slightly higher electric bill and having a unit that just barely covers the load. I am all for sizing as close as possible to load and think a 3 ton would work with either backup heat use or loss of comfort(lower indoor temp), but drlebel should at least know the differences. Today it may not make a huge difference because even needing 15K BTU's of extra heat is only about 5KW and if it runs for an hour, you will only use $.50 extra electricity(based on $.10 per KWh), but lets say you need it for three days, its still only an extra $36. However we don't know what electric prices will do and if we do switch to time of ouse pricing you can bet that when your house is running on backup electric heat is when the price is highest. So if we assume a $.50 per KWh price which I have seen predicted during extreme peak usage(1% design days and temperatures below) now its $180 extra for three days worth of 5KW of backup heat. I have seen estimates that we switch to these pricing models in 5 years, hopefully we don't but some areas are already implementing and in Portland our electric company just switched out meter heads so they can adjust pricing based on time of day. If we do switch that $180 per year of backup heat quickly adds up to just upsizing the system to a 4 ton unit. At the very least you are hedging your bets. Just a second opinion on your sizing dilema since most people purchasing a geo are looking long term and new electric rates will affect that long term outlook.

It's not that I'm forgetting- it's that I'm IGNORANT!

Not being a GSHP system designer I have no insight into the derating details- thanks for the clarification!

So, for us amateurs, guesstimating the output by nameplate tonnage of a 3-4 ton GSHP should be 70-88% of the pump rating? (Something crudely akin to multiplying by the input BTU by steady-state efficiency number of a fossil burner to estimate the output, though the units & meanings are completely different.)

I was led astray by blindly assuming the nameplate ratings on equipment has a closer relevance to the actual output, at least in an optimized design. With fossil burners the DOE rated output on the nameplate is pretty-much what you get out of it in a reasonably designed system. With mini-splits the nominal sizing is a cooling BTU rating, which is lower than it's heating output until fairly cool outdoor temps (like 0F), but max heating capacity is usually specified at a few outdoor temps even on the short-sheet specs.

Peeling another 15KBTU of peak heating load may be doable with some carefully places/priced insulation upgrades for that extra $1000 too but probably not. It just depends.

I would not expect to see heating season 30-40F EWT in Memhpis, TN (deep soil temperature ~62F) unless his geo loop is under designed for the desired BTU load.

Regardless, my selection would likely be a 4 ton two-stage or multi-stage heat pump for this application given the numbers presented. A Climatemaster Tranquility 27 or 30 two-stage unit would satisfy both your heating and cooling loads since 1st stage operates at ~2/3 of unit full load rating.

2 stage units on closed loops are rated systems for cooling capacity which is typically higher than heating capacity. 12000 btus/ton in cooling mode (78F), and roughly 9600 btus/ton in heating mode at 32F EWT. Things change again with the variable speed compressors, which are rated higher in heating mode than in cooling mode.

Avoid use of "typically" when comparing cooling vs heating capacity. Everything is relative to deep ground temp
Memphis 63
Portland 54
Buffalo 50
Jacksonville 71

Assuming EWT peak / valleys at +/- 20 deep ground temp, a Buffalo system had better be sized to heat at 30 EWT, whereas a Jacksonville system had better be sized to cool at 90 EWT.

Available BTUH / ton for design purposes should be based upon local conditions.

Memphis is a sweet spot - EWT above 40 winter, below 85 summer; what's not to like?

I stand by my stance that a 3T may be the right answer id accompanied by just a bit more envelope load reduction, summer and winter.

Posted By engineer on 14 Nov 2012 10:51 PM
Avoid use of "typically" when comparing cooling vs heating capacity. Everything is relative to deep ground temp
Memphis 63
Portland 54
Buffalo 50
Jacksonville 71

Assuming EWT peak / valleys at +/- 20 deep ground temp, a Buffalo system had better be sized to heat at 30 EWT, whereas a Jacksonville system had better be sized to cool at 90 EWT.

Available BTUH / ton for design purposes should be based upon local conditions.

Memphis is a sweet spot - EWT above 40 winter, below 85 summer; what's not to like?

I stand by my stance that a 3T may be the right answer id accompanied by just a bit more envelope load reduction, summer and winter.

Local conditions influence the design of the loopfield. It is a common misnomer that (obviously not for Curt) loop temps are stable. The load determines the peak EWTs. If you are getting not below 40F in the winter and not above 85 F in the summer, chances are that your loopfield is larger then needed and you paid too much upfront, and don't get a good ROI.

Thanks y'all, the discussion is great. This will be a closed loop to a 3 acre pond if that changes anything regarding ground temps. I guess im leaning to a 3 ton 2 stage climatemaster with some heat strips. I also have 2 propane fireplaces with blowers for emergency heat if needed fro record lows. The waterfurnace looks nice but its pricey and my installer doesn't normally install that brand.

Posted By engineer on 14 Nov 2012 10:51 PM
Avoid use of "typically" when comparing cooling vs heating capacity. Everything is relative to deep ground temp
Memphis 63
Portland 54
Buffalo 50
Jacksonville 71

Assuming EWT peak / valleys at +/- 20 deep ground temp, a Buffalo system had better be sized to heat at 30 EWT, whereas a Jacksonville system had better be sized to cool at 90 EWT.

Available BTUH / ton for design purposes should be based upon local conditions.

Memphis is a sweet spot - EWT above 40 winter, below 85 summer; what's not to like?

I stand by my stance that a 3T may be the right answer id accompanied by just a bit more envelope load reduction, summer and winter.

Typically was referring to rating conditions. I was trying to make the point that two stage units' tonnage is rated higher for cooling than for heating at standard rating conditions, but this is not the case for the newer variable speed units.

I wonder if that is because the cooling rating EWT (59, 77, 86) are below or just a bit above indoor design air temp (75) [and we are content with supply air 20*F below that].

OTOH in heating, EWT is 30+ below indoor design temp (70), and we really prefer supply air 25+ above that. In other words, there is a lot more "lift" in heating mode

OTOOH, compressor power is added in heating mode only.

I was thinking among the same lines. Much lesser lift in cooling mode, although the compressor heat needs to be rejected as well. But the much lesser lift seems to outweigh this.

"So, for us amateurs, guesstimating the output by nameplate tonnage of a 3-4 ton GSHP should be 70-88% of the pump rating? (Something crudely akin to multiplying by the input BTU by steady-state efficiency number of a fossil burner to estimate the output, though the units & meanings are completely different.)"

Well no not exactly, output of a heat pump is generally an indication of cooling capacity. This capacity is impacted by entering water temperatures and entering air temperatures.
Fossil units are also impacted by EAT and fuel (btu/cu foot or gallon vary). For instance they get a reduction in efficiency at different EATs. Different efficiencies mean different out puts. Air source systems are also impacted by oside air temps as you know, so it's same regardless of equipment type: most, put out least, when needed most.
In the case of heat pumps however (air or ground source) we have auxiliary heaters so we can design tighter.
I already design in auxiliary (3 tons for 42,000 btus for instance) but there is no auxiliary AC so strategies vary be region.

"OTOH in heating, EWT is 30+ below indoor design temp (70), and we really prefer supply air 25+ above that. In other words, there is a lot more "lift" in heating mode"

That's why people get confused on heating vs cooling dominated climates.
A home in TX may see 35 degree lows in the winter and only 100 in the summer. So since I have more "lift" in the winter is this not a "heating dominated" climate?

"To me it comes down to would you rather spend the extra $1,000 for a 4 ton with extra ductwork and ground loop"
Wait you pay $600 for the extra ton of equipment but only $400 for extra duct and loop? You are hired! That's less than my cost.

Bin hours?

Jax outdoor design is 32 winter, 94 summer, but it feels like 94 for about 4 months per year, but 32 for only about 4 nights.