I’m investigating the replacement of the 10 year old 3 ton (undersized!) Frigidaire packaged heat pump that came with our house with something newer, more efficient, with good reliability, and much quieter than the rated 74 dB we have now. Packaged units (I’ll use “PU”) seem to get zero to little attention by manufacturers as far as making newer, higher efficiency designs. At best I find variable speed blowers and 2 stage compressors that yield HSPF 8-8.5. We have 10 kW strip heaters for backup. The only power source we have is electricity.

We live in the Northwest where design temp is 17F. In my experience it is common to have cold winter nights in the mid-20’s, so strip heaters (or the wood fireplace insert!) come on routinely. Our house is a 3750 SF rambler roughly 40 ft wide x 80 ft long, and the PU is at the very end of the house along a 40 ft wall, just outside our bedroom. The duct work is in the crawl space and has been upgraded by me to all metal, insulated, with the main line running the 80 ft length of the house, with side branch runs as needed. There is one return air vent in the hallway 20 feet from the PU, so a short run. Measured static across the PU supply-return is 0.24, however 0.12 of that was separately measured across the new 4″ air filter, so duct system should be 0.12 as well.

Based on the existing Frigidaire spec and real world performance of seeing a 30F balance point, I’ve made a straight-line plot of our passive heat loss at any temperature: At 17F we lose 37,500 BTU, at 25F it’s 31,000 BTU, etc.

我正在查看（到目前为止）使用PUZ-HA36NHA5热泵MITS PVA-A36AA7。该装置的最大容量为17F的38 MBTU。问题是空气处理程序旨在在室内进行。我努力避免大规模的管道工作重新路由，并希望考虑在外面安装空气处理程序。我们有4英尺的屋檐，所以它会在外面受到很好的保护。我可以在房子里建一个“狗屋”进一步保护。PVA配有R4.2绝缘，但如果需要，我可以增强这种情况以防止凝结。需要创造性的导管，以使现有的并排供应/返回管道（其中PU接口）调整到PVA型流动。

Q1：是否有任何关于更换包装单元的其他想法，具有更常规（和共同）热泵设计，而不会疯狂地达成疯狂？

Q2: Any issues with installing the indoor air handler in an outdoor dog house?

Q3: I can still consider a replacement PU but it would need to be 4 ton minimum due to the performance drop at low temps, and that would give me a BP of about 25F using Goodman and similar online specs. 5 ton only 22F so not much extra bang for the buck, plus air flow requirements go up.

I would appreciate your thoughts and suggestions. Thank you!
罗恩