PDA

View Full Version : Cascade AWHP Design using R-410A & R-134A







bmaneckjee
24-08-2013, 02:35 PM
Our company has been involved in the manufacturing and distribution of AWHP's for 7 years. Current models use conventional 1&2 stage Copeland Scroll R-410A condensers with an indoor split evaporator using a coax HXG, a mixing valve and internet enabled controls. We've been successful meeting the needs of the Canadian coastal market with hydronic floor heating applications where water temperatures so not exceed 120F.

However, we are now working towards a high temperature design and our secondary research suggests that using an R-410A & R-134A cascade design may be the most pragmatic approach to obtaining water temperatures in the 170F range. Our company specializes in North American residential products so we are limited to input power of 240/60/1 which is making it difficult for us to find the 2nd cycle R-134A compressor. Specifically we're looking for an R-134A compressor with input power of 208-240V, 3P, 50/60 Hz since we'll be using a VFD to modulate the 2nd cycle to match the heat output of the fixed first R-410A cycle. All installations include a buffer tank so we're not trying to modulate output as a whole and are satisfied to meet the output of the R-410A cycle over the range of 65-5F outdoor ambient temperatures experienced within our target market.

We would like to build units with a total output equivalent to 5-6 ton heat pumps and consequently expect we will need compressors in the range of 2.5-5 tons. We are under the impression that a cascade design output is a sum of the output of both cycles but would like confirmation from anyone with experience with these systems to confirm so we can look for the right size compressors. So far we've found that most hermetic R-134A compressors are produced for the auto and refrigerator market and tend to be smaller than what we think we'll need. The other problem is that some larger models we've found all use higher voltages suitable for the EU/Asian and commercial markets.

I'd appreciate it if anyone with practical experience and knowledge with designing similar cascading cycle heat pumps would contact us and/or offer their insights on our current approach and offer any assistance sourcing the elusive R-134A compressor we're looking for.