Replies

1. GBA编辑器
   Martin Holladay|Mar 03, 2015 05:51am|#1

   Apollo,
   To get 100,000 BTU output from a 75% efficient boiler, you need to input 133,333 BTU of gas. That's 1.33 therms of gas, which costs you exactly $2.00.

   获得100,000 BTU（29.3千瓦时）从带有2.6的COP的导管MiniSPLIT输出，您需要输入11.27千瓦时的电力，费用为2.74美元。

   因此，在MinSplit的Cop上升至3.56之前，MiniSPLIT不会更便宜。

   If you can find a graph that shows you the outdoor temperature at which the COP of the minisplit rises to 3.56, you'll know how warm it has to be outdoors for the minisplit to save you any money.

2. Expert Member
   Dana Dorsett|Mar 03, 2015 02:00pm|#2

   没有单一的COP与温度图，也不是可以存在的。超大因素和调制水平对其运行效率有很大影响。如果它在其最大容量的一半运行，则2.6警察将在极端的低端。

   它可能提供一个警察@华氏40度即使它更好's running both the compressor and the heads at max speed, but the heat load of the house at 40F may only be half it's max output, so it'll be doing something like 3.5-4. Without modeling the heat load of your house relative to the outdoor temps it's impossible to say where it will be in it's modulation range.

   看看提交表：

   http://usa.mylinkdrive.com/uploads/documents/4342/document/MXZ-2B20NA-1_Submittal.pdf

   http://usa.mylinkdrive.com/uploads/documents/4331/document/MXZ-2B20NA-1_for_E-Star_Submittal.pdf

   笔记that at +17F if you're only operating it at 12,500BTU/hr of output its only pulling 1350watts. At 3.412 BTU/watt-hour that's 4606 BTU of input, for 12500 BTU of output, a COP of about 2.7, even at that low temp. But your heat load is probably over 12,500 BTU/hr @ +17F, if your house is old enough to have a steam boiler.

   At 47F the GE06 + GE09 combination can deliver the full 25,500 BTU/hr, but it takes about 1650 watts to get there, which is 5630 BTU/.hr of input, for a COP of 4.5, and that's a max speed (!). But since your heat load at 47F is only about 10-15K, it'll be doing better than that, maybe bumping on 5.

   If you look at page 3, at +17F GE06 + GE09 combination can deliver a max of (7400 + 11,000= )18,400 BTU/hr. But to deliver that it's using 2250watts, or 7677 BTU/hr of power to get there, which is a COP of only 2.4.

   为了估算交叉点，首先需要了解跨越温度的热量负荷（这是大致线性的），您可以从中估计多分裂的调制级别。在提交表中提供的曲线上的少数点，您可以在预期的调制水平下插入近似警察的近似警察。

3. 
   阿波罗斯|Mar 03, 2015 02:30pm|#3

   Martin and Dana,
   谢谢您的回答。学到了很多东西。

   Part of the house that is served by steam and mini-splits was built in '38 and gut-remodeled in '55.

   我通常在一个MiniSPLIT和6K头上运行9K头。令人惊讶的是，他们似乎能够迅速地获得房间，而不进入最大模式。另外两个头在较不少的使用的房间里，因此他们在大部分时间都不在，因为这些房间坐在55°F。我也不会将房子加热到70F，因为大多数设计日期都是如此，68F在当天只有4个小时，休息一天，我将房子留在62°F，晚上64F。

   Manual J wasn't done that well, but contractor calculated that portion of the house we could heat with minisplits at needing about 20818 Btuh. Code level insulation in the attic and new windows, but empty walls.
   I think that is for 1400sq ft, if I am reading manual J right. I am probably heating half that with steam or minisplits. Other side of the house is forced air with 97%AFUE furnace, so not part of this conundrum.

   建筑师我们正在采访我们的能源改造和改造是那个真正怀疑我的40F甚至粗糙的计算的人。

4. Expert Member
   Dana Dorsett|Mar 03, 2015 03:19pm|#4

   Using deep setbacks with modulating heat pumps generally uses more power than if you kept it at a constant temperature or with minimal setbacks. This is because it operates at substantially lower efficiency during the recovery ramp (even if it's not at max-speed) than if you just let it modulate at part load all the time.

   在白天62F到68F的6F摆动可能是使用更多的功率，而不是整天保持66-68F。在白天，室外温度较高（=在任何给定速度下效率较高），并且热负荷降低（=较低的调制水平，这意味着更高的效率）。通过让室内温度下降，降低热量损失率，恢复坡道期间的效率差异将会“拯救”时间为最佳6％。

   The guy in this study who was basically setting back 10F whenever he was away ended up using 57% more power than folks who kept it in a range. See Figures 27 & 28 and Figure 40, and the text discussing how the mini-splits were used for Lot 23.

   http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/monitoring-mini-split-ductless-heatpumps.pdf.

   让事情调制，并且只踩它以上或向下处理设定值和与负载相关的实际房间温度之间的偏移（当迷你分裂仅在头部的传入空气温度感测到常见问题时，而不是平均值房间空气）（差不多）总是可以使用少于每天多次上下逐步下降的力量。

   At current IRC 2012 code min most 1400' houses would have a heat load at +12F (Boston's 99% temperature bin:http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf）整个房子的20,000 btu / hr井，更不用说一个区域。墙壁没有绝缘，但近期U0.34窗口和阁楼里的R30 +你可能看起来像整个房子25-30K这样的东西，只有一半的房子。如果让迷你分裂调制它们将在20S F中以低速/高效率深度怠速，如果3.5的COP是魔法财务交叉点，那可能发生在低30秒的某个地方鉴于您的超大因素，但没有更多的信息，而不是适合网络论坛分析这几乎不止摇摆。

   A 75% steady-state efficiency of a steam boiler does not translate into it's as-used AFUE. If you're heating mostly with the ductless units it's duty cycle is much lower, and heat-up & standby losses much higher. The net result is a higher heat loss out of the boiler room (due to higher boiler room temps) and higher distribution losses, more heat being "abandoned" in the boiler. At the very low duty cycle your real AFUE is probably more like 60%, 65% tops, assuming a steady state combustion efficiency of 75%. If the ductless keeps up with the heat load it's probably better to just moth-ball the steam system, or set the thermostat to 5F below the ductless setpoint(s) as the Hail Mary backup for those 5 days per decade when the outdoor temps drop below 0F, (assuming the ductless won't keep up then,)

   This winter's high electricity price is a fluke, with the generating companies recouping their losses from mis-managing the natural gas grid capacity constraints a year ago. It would be surprising if the rates were more than 20cents next winter, given the increased regional liquified natural gas (LNG) capacity, and the wiser management thereof by the generators and gas utilities after last winter's financial disaster (that we're paying for in this winter's rates.) Under MA regulations they are only allowed to adjust the rates 2x per year- expect a big discount starting late this spring. But since they didn't set back on their heels by the severe constraints that had them scrambling to fire up #2 oil peakers just to keep the lights on last year,it's unlikely that they would get the same rate increases approved for next winter. The price of both #2 oil & LNG is substantially down compared to last year, and even during the cold snaps they didn't hit the gas-grid limits, despite even cooler weather than last year. Unless something drastic happend, you should probably pencil out the crossover point using $1.25-1.40 natural gas at 60% efficiency and $0.18-0.20 electricity at a COP of 2.8-3, if looking at next year.

5. 
   阿波罗斯|Mar 03, 2015 03:56pm|#5

   Dana,
   这是非常有帮助的，消化很多。

   Those deep setbacks I came to exclusively for steam. I did several months of experimentation and together with stepped recovery in temps. I start heating at 5PM in stages, I let thermostats catch up to radiators heating space, and by 7PM, when we get home, two boiler cycles make up the difference. This setup cut about 10% compared to 4F setback during the day and 2F during the night. Comparison was done by manually recording the meter reading every day. Granted, my steam system is not piped right and radiators are undersized in one area and oversized in another.

   Heat-pumps I have used maybe for a week at different times. I know it costs me $18 per day to heat the house. Going to experiment in the coming month by letting minisplits work in 20F+ weather and boiler for below that.

   我真的真的在调查光伏。有很多东西和西屋顶空间不含羞。我的妻子不是蒸汽的粉丝，我们非常活跃的小孩跑来跑去。那些RAD得热。