Verifying the a/c installation

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ARPE
Posts: 52
Joined: Mon Feb 20, 2017 7:02 pm
Location: Miami Beach, FL

Verifying the a/c installation

Post by ARPE » Tue Feb 20, 2018 8:04 pm

I got my Bavaria R40 and started getting to know the boat. The first thing I noticed is that the boat has four a/c units (2 of 8K BTU and 2 of 12K BTU). The two small size ones serve a berth plus a head each, the two larger ones serve the galley area. Although 24K BTU seems a good size at first glance, I am not sure it is properly sized for summer in South Florida.

I decided to review the installation to ensure the air flow distribution is optimized to take the most of the a/c units. The return air inlets seems sized to minimum limit and the supply air seems undersized (when compared with Dometic recommended sizing shown in the table below). I am posting this “kick-off” here and will be posting my conclusion as reply to this post.

The table attached may be useful to you as it covers other a/c sizes, I took it from the Dometic installation manual
46D1EC32-0545-4434-9982-7C56C1118213.jpeg
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2018 Bavaria R40 Coupe, D6-370
2015 Regal 35 Sport Coupe, D3-220 - Sold

User avatar
ARPE
Posts: 52
Joined: Mon Feb 20, 2017 7:02 pm
Location: Miami Beach, FL

R40 Cabin a/c located under co-pilot seat

Post by ARPE » Wed Feb 21, 2018 5:07 pm

The unit is installed under the co-pilot seat and serves a single grill, located in the top cabinet near the back door. By inspection I found the following:

1) Air return
The return grills have filters and the a/c unit has a filter. Besides the two return grills, there is also a disguised return without any filter (in the picture I am pointing to the disguised return).
image1-1.jpeg
My first step was to remove the return grill filters. The picture shows the filters, it is simpler to remove from the interior side.
image2-1.jpeg
The return area is 2 times 4.25" x 11" (two return grills) plus 28" x 1" (disguised return), this gives us and area of 121 sq in. Dometic requires 130 sq in, hence this is adequate given that there are other not accounted for small air intake holes.

2) Air supply
A 6" isolated pipe runs straight behind the cabinets and then up to the upper cabinet supply grill. There are three 90 degrees curves (at a/c exit, horizontal2vertical, vertical to grill area).

Bavaria installed a return grill with filter instead of t a proper supply grill. My short term correction was to remove the filter, but I will replace return grill by a proper supply grill to be able to change the air flow direction.
image1-2.jpeg
The supply area is 4.2" x 11", which is 46 sq in, Dometic recommends 70 sq in. I am investigating if the pipe should be split to serve a disguised supply opening of 3.2" x 4", which is 12 sq in. This would bring us to 58 sq in, which is closer to Dometic recommendation.
image2-2.jpeg
I can already see major air flow improvement after the removal of the three filters, we still have the potential for further airflow improvement with the splitter. Another pending improvement is the replacement of the return grill used by a supply grill as it will allow diverting the air flow to the ceiling when desired.
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2018 Bavaria R40 Coupe, D6-370
2015 Regal 35 Sport Coupe, D3-220 - Sold

User avatar
ARPE
Posts: 52
Joined: Mon Feb 20, 2017 7:02 pm
Location: Miami Beach, FL

R40 Fwd Cabin located under the floor

Post by ARPE » Fri Jan 18, 2019 8:35 pm

The unit is installed under the floor at the entrance of the fwd cabin and serves the fwd cabin plus the bathroom through air exits disguised on top of the port cabinet. By inspection I found the following:

1) Air return
There are two return grills which filters and the a/c unit has a filter. I removed the return grill filters, it is simpler to remove from the interior side. The interior side can be reached by raising the floor carpet and opening a wood cover. The return area is 2 times 4.25" x 11" (two return grills without filter), this gives us and area of 93 sq in. Dometic requires 80 sq in, hence there is adequate return holes.

2) Air supply
A 5" isolated pipe runs behind the starboard cabinet. Bavaria connected the 5" pipe to a 4" adapter.
Adptor 4.jpeg
fwd cabin pipe.jpeg
The supply area, given the 4" adapter is 12.6 sq in, Dometic recommends 19.6 sq in duct. I removed the 4" adapter, increased the diameter of the hole on the wood cabinet to 5" and installed a 5" adapter. The comparison picture shows how significant this increase in diameter is.
Comparison 4x5.jpeg
Wood hole.jpeg
The supply is now through 19.6 sq in as recommended by Dometic.

I believe those small changes made noticeable difference to fwd cabin and bathroom cooling.

Note: The installation of a 5" duct to a 5" adaptor is much cleaner and reliable than the factory-installed 5" duct to a 4" adaptor. Enlarging the wood hole is necessary to get the benefit of smoother air flow.
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2018 Bavaria R40 Coupe, D6-370
2015 Regal 35 Sport Coupe, D3-220 - Sold

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