I am looking for advice on how to cool my basement in the winter without using/wasting too much energy. I thought this would have been simple/easy to accomplish, but I am finding that it is not.

If anybody has any ideas about how I might practically accomplish this, I'll be very interested to hear them!


The Setup

I've got a house with two stories plus a basement. I run a lot of hobby-related computer equipment in the basement, which means it is quite warm down there year-round. This is fine when I am sitting down there doing hobby stuff, but makes me miserable and sweaty when I exercise on the treadmill.

I have a zoned, variable-speed Bryant HVAC system (987M furnace + 3-ton 186CNV air conditioner)  here. The basement is on its own zone, and its ductwork is capable of handling the entire ~1,200 CFM airflow of the air conditioner running at its full 3-ton capacity.

When the weather is relatively warm out, the HVAC system works great. I crank the basement thermostat down to the desired temperature. The air conditioner kicks on at a relatively high output and quickly pulls the basement down to the new setpoint. Once the system brings the temperature near the setpoint, the compressor and blowers throttle back to fairly low RPMs and run very efficiently to keep the basement cool.


The Problem

The problem starts when it is cold out and I want to cool the basement. Under these conditions, the system always runs the compressor at high speed (and thus high power consumption) even when the demanded cooling CFM are very low. I asked about why it does this here in r/hvacadvice some time ago and was told that the compressor needs to run at a higher-than-otherwise-needed RPM in these low ambient conditions in order to maintain appropriate working refrigerant pressures in the system.


Numbers/Facts

As an example, I used the air conditioner for 2.5 hours yesterday to bring the basement from a starting temperature of 75 degrees to a setpoint of 68 degrees. The outdoor temperature was around 30 degrees (Fahrenheit) at the time.
As expected, the system very quickly brought the basement down to 68 degrees. But even after doing so, the compressor never throttled down to low RPMs (or low power consumption) as it would normally do once it was just maintaining the temperature near the setpoint. The system used a whopping 3.6 kWh during this 2.5 hour period as shown here:

https://i.imgur.com/V73h1oc.png


If it's cold out, why don't you just open the #$%@ windows?

I would, but it's a basement; most of the walls are underground. There are block windows up near the ceiling, but only two of them open, and the openings are quite small (about 16"x5", but the open/close mechanism blocks a lot of the opening area even when open) so even with them open, not a lot of cold air comes in.


Ideas

I've had a few ideas about how to improve this situation, but they all seem pretty bad/stupid in one way or another:

* Put a ~1 kW bounce-house blower outside pointing into one of the windows

I imagine those things could probably blow quite a few CFM against a fairly high static pressure, but it seems like it might be loud enough to annoy the neighbors (and me, maybe), and also I doubt they are designed to sit outside 24/7.

* Buy the cheapest possible mini-split air conditioner and put the compressor/condenser unit in another room of the house. There would never be low-ambient operation this way, and the unwanted basement heat could usefully heat the rest of the house.

This one seems like it would be decent from a thermodynamic / energy efficiency standpoint. But I really don't think I want a mini-split outdoor unit sitting in my living room.

* Quit being a wimp and just deal with the basement being hotter than I want

This is not a solution to the problem. The whole point is that I do not want to just put up with the warmer-than-wanted conditions.