This is a continuation to a previous post carver p4 furnace for isolde- part 2. In 1999 I was one or the first group of customers purchased one of the Carver P4 furnace brought in by a small US camper aftermarket accessories vendor. The vendor was importing them in quantities of 10 or 20 units at a time in which the customers pre-ordered the purchase.
Only a year or so before that I installed a Volvo marine propane furnace into his Westfalia Vanagon Syncro Camper. At the time the Volvo was the only compact propane furnace suitable for the interior size of Vanagon. The Volvo furnace puts out plenty of heat and was made in Sweden. It is built like a Volvo 144 sedan in which function dictates form. It gets the job done and takes no prisoners. It was loud.
When I saw the Carver P4 furnace's specifications and product description I had to have one. I joint the first group of the pre-order and a month later the unit arrived. It has a nice looking industrial design case, and a handsome user control panel with tasteful graphic and fonts. Carver at the time was a small UK company specialized in heating products for caravans. There were many products before the P4 including water heaters.
Helping my friend installing the Volvo furnace prepared me well in the planning and the design of the installation of the Carver. As the installation of a forced air furnace entails cutting holes into the Westfalia cabinetry I spent considerable amount of time considering all relevant issues. Where is the best place for the heater, the comfort heat outlet and return ports, the routing of the fuel gas, combustion air intake and flue exhaust. Even the location of the user control panel was carefully mapped out.
The Carver furnace must be installed flat. Given the arrangement of the fuel gas supply port, the combustion air and flue ports the installation location very quickly narrowed down to inside the bench seat.
The design of the Carver furnace utilize a rheostat for user temperature control. The heater controller regulates the heating by constantly sampling a thermister located at the return air duct of the heater. The rheostat is just a potentiometer that the user indicates to the furnace controller the desire target temperature. Hence the main consideration of the location of the user control panel is convenience of use, ergonomics, and visual aesthetics. I chose an elevation above should height when one is leaning again the closet wall. I want it high enough so it would not sacrifice the comfort when one leans against the closet like reading or lounging in bed. I also want it not too high that is hard to reach when lying down in bed. The final location was a balance of these and the visual aesthetics.
the chosen location for the user control panel; it is also within easy reach when one is seating on the bench seat
The cable that connect the user control panel and the furnace utilize a RJ45 plug as found on Ethernet cables at each end. During the initial installation I was unable to feed the RJ45 plug through the tight gap under the closet and the Vanagon floor pan. All I had to do is to snap off the RJ45 plug and feed the cable through and then crimp on a standard RJ45 plug back.
Because of the slope back wall inside the bench seat, the width decrease downwards. There is not enough width to accommodate the Carver furnace and the bending radius of the combustion air and flue stainless steel hoses if it is mounted low. I fabricated a mounting pedestal out of 3/4 inch plywood to elevate it.
plywood pedestal - the bevel side butts up against the back wall inside the bench seat; the slot on the leg is for air supply to the Vanagon heater insider the bench seat
the pedestal is fastened down through a piece of aluminum angle at both ends; shown here also is the propane copper tube supply rise from under the floor pan
The Carver furnace is supported by 4 sheet metal mounting brackets, each with a rubber gourmet to isolate vibration. Both the intake air supply and the flue exhaust are routed to outside the cabin via flexible stainless steel hoses. The flue hose is further encased inside an larger diameter aluminum flexible hose.
the pedestal shelf is notched on one corner to accommodate the passive crossover of the left channel speakers of the 3-way MB Quart component speakers
these photos were taken before the recent major electrical update in which the Vanagon rear heater was eliminated to make room for 2 group 24 deep cycle batteries
it is bigger than a Propex of comparable wattage but the quieter and much more refined operation are the benefits
these are the comfort air vent ports that ware made in Japan; very well designed and made
the air flap can be set at any angle as well as rotate in a groove to point to any angles
thanks to the double wall flue exhaust there is no danger of fire should any combustible object comes into physical contact - note the solid aluminum collar that keep the two hoses concentric where it is the hottest
the cable ties have secured these hoses for 16 years now; I did this because I wasn't sure if this would be the best location for them
by placing the intake and combustion exhaust adjacent to each other the furnace operate even at highway speed
When so many major appliances are fueled by propane it is the most unpleasant experience when one runs out of propane in the midst of a camping. I installed a second 3-gallon tank. By drawing from one tank only I would know when the first one is depleted. I can manually switch over to the backup tank, and dead reckon the usage until the first opportunity to refill both.
as part of the furnace installation I added a second 3-gallon tank on the passenger side
this is a more recent photo with the two newly installed group 24 deep cycle batteries
The most distinguishing features of the Carver P4 furnace that sets it apart from other small camper furnace is its extreme low power consumption, whisper quiet operation, and even temperature. The furnace has two user select kW levels - low (1100 kW and high (2200 kW). One should not confuse this two kW levels with temperature setting. The two kW levels give you the benefit as if you have two furnaces. The low setting has a smaller flame and the high setting has a flame double that of the low. The clear benefit is you enjoy quieter operation when the weather is milder and yet have a bigger furnace when the weather is very cold. The electric power consumption at low setting is roughly half as both the blower motor and the comfort air circulator run as lower speed.
Additionally the circulator blower speed is constantly being regulated to maintain near constant temperature at the heat outlet vent. That is the blower speed is proportional to the temperature of the heat exchanger. It is very revealing to pay attention to the blower fan speed, as well as the current consumption by the entire furnace through out an ignition cycle till the next. The heat exchange has a rather big thermal mass that you can infer. After the flame stop, the circulation fan will go on for minutes outputting warm air on the outlet for minutes. As the temperature of the heat exchanger drops the circulation blower speed is gradually reduced, hence maintaining relatively constant temperature. Once at steady state and no calling for heat is requires the circulation blower is reduced to a murmur; and the entire furnace consumes only 150mA! This including two micro-controllers and the circulation motor.
The operation sound of the furnace at low is so quiet that even when sleeping in the still of nature one have to press the ear on the pillow to be able to tell if the burner is firing.
The circulator blower never stops but runs very slowly to circulate the cabin air. The cabin air temperature is sampled by the microcontroller at the return duct of the furnace. When the heat exchanger cools down the entire furnace can draw as low as 150mA (0.15A). Because of this the cabin temperature is regulated more tightly than a design utilizing a remote thermostat.
When the burner is on the current consumed is about 1.08A at low, and 1.75A at high.
furnace set to low - flame on; consumes 1.08A of current
furnace set to low - flame off; comfort air modulated to slowest speed; consumes 150mA of current
So how does it stack up the competition? No contest. Shortly finding out Truma has acquired Carver and discontinue the P4 I bought a Propex HS1800 as a backup in case the Carver becomes unserviceable. At the time both the Carver and Propex are like grey market imports into the US. Compare to Carver the Propex is annoyingly loud and unrefined. It has a constant burner blower as well as the comfort air circulator motor (I suspect there is only one motor that performs both functions). With the Carver even the burner noise level outside the vehicle is very quiet and discrete, making it ideal for stealth camping. With the propex, you might as well as lighting a neon sign that live occupants inside. There is simply that much more in the Carver furnace than anything out there.
A detail analysis of the Carver P4 design can be found in this post - carver p4 furnace for isolde - part 2
For comparison, I also dissected the Propex HS1800 in this post - inside propex hs1800 - first look
No comments:
Post a Comment