Variable Speed Refrigeration and Air Conditioning Compressors
I recently had an air conditioning system replaced at my house. Out went the old energy hog with a noisy, fixed speed compressor, and in came a high efficiency unit with a quiet compressor and fan, both of which run at variable speeds. So, today’s question is: Why does varying the compressor speed increase efficiency, and how is that achieved?
Golden Rule: The longer and slower a compressor can run, the more efficient it will be
Efficiency in refrigeration and air conditioning systems is measured as a ratio of power out to power in, and can be in several forms. The Energy Efficiency Ratio (EER) is the ratio of output cooling energy in Btu’s to input electrical energy in watts under certain fixed conditions. So a system with an EER rating of 10 will produce 10 Btu’s of cooling for every watt of power consumed under the specified conditions. The Seasonal Energy Efficiency Ratio (SEER) that is used in commercial and residential equipment is similar to the EER, but is assessed over time and under varying conditions.
When a fixed speed compressor is operating under light-load conditions, i.e. nighttime, cool weather, etc., a fixed-speed compressor will be running for short spurts and do a lot of cooling in a hurry, which is inherently very inefficient. If we were to be able to slow the compressor down during periods of light load, the system would run longer and be more efficient overall, but would still have the required capacity available for high heat-load conditions.
That "W" word... Warranty
At dealer technical training sessions run by marine equipment manufacturers, typically the last item on the agenda before everyone heads off home is the matter of warranty.
The cynical among us might think that this is so timed that it can be rushed through at the last minute so the factory staff can shrink from the baying crowd and make a swift retreat, and that may not be too far from the truth. But why is it sometimes such a contentious subject?
From a new-boat owner's perspective, it is entirely reasonable for him or her to assume that if anything fails on a newly purchased vessel within the warranty period it will be replaced or repaired without too much fuss and bother.
But, unlike an automobile where the car dealership is responsible for repairs to every item on the vehicle, equipment on pleasure craft is supplied by individual manufacturers, each with their own warranty policy.
Wind Generators-are they the better choice for power?
Here at Coastal Climate Control, we talk to a lot of boaters at shows and in the course of daily business, and in general, most of the people we talk to who have wind generators seem to be less than ecstatic about their performance.
We commonly hear gripes that what these device's specifications promise on paper seldom seem to materialize in real life application. And then the cost, complexity, and effort of installing wind generators apparently put a lot of people off, not to mention the unease of having sharp-edged blades whirling away within a daggers-throw of one's head!
Some wind generator owners report that their systems perform well on passage, when the boat is beating into the wind, although it is well known that gentlemen never go to windward ... but then when the destination is reached and the hook dropped in the sheltered anchorage of an island, the wind generator seems rarely to have the oomph needed to fully charge the battery, at a time when reliable charging is most needed.
So, have wind generators had their day?