Assess and quantify the benefit of alternative and renewable energy for greenhouse operations

The use of Waste Vegetable Oil (WVO) has been problematic. Some of the problems have been due to our
approach, and some are endemic to the nature of WVO as a fuel. In the end, most of the significant problems
were solved or reduced to manageable proportions and we are comfortable using WVO. Certainly the cost and
environmental benefits outweigh the few remaining difficulties.
Here are the primary fuel considerations:
Waste Vegetable oil- vTVO
The fuel itself has proved to be the cause of many operational issues that are separate from issues that are
specific to the equipment or installation.
1. Fuel Sources - Of the various cooking oil products used in the food service industry, the best to use for
heating applications are liquid, non-hydrogenated oils such as peanut, canola, or corn oil. This is often
provided as a blended product to the restaurants. Cooking causes a partial breakdown of the oil, and it
will stay liquid well below 32 degrees F. Finding a regular source of WVO has been difficult. The best
kind of oil is commonly used in Asian restaurants, but sometimes it is difficult to communicate with
owners in order to establish a relationship what will allow us to collect the oil. Even restaurants that
are willing to give us oil are often unwilling to give up their contract with the local renderer.
2. Collection Difficulties -Initially we collected our own oil from local restaurants. Most restaurants have
a dumpster or barrels that are placed by the rendering company that they are contracted with for oil
removal. Technically, the oil becomes the property of the rendering company when it is placed into
their dumpster; which means that even if the restaurant owner agrees to give oil to us, we cannot
legally remove it from the dumpster. The restaurateur must package it separately, or we must provide
our own dumpster or barrel.
3. Contamination - Often, water, food waste, and other contaminates are in the oil we collect from
restaurants. This puts a heavy burden on us to let the water settle out and filter the oil. Contaminates
such as flour and batter remnants, peanuts, and other small particles are hard on pumps and filter
elements. In a few cases, we have been successful in convincing the kitchen staff to avoid putting
excess contaminates in the oil, but this is a constant battle. Oil collected from hospital kitchens and
donated to us by Biomedical Waste Systems proved to be of such poor quality at times that it had to be
discarded. After BWS interceded with the hospital kitchen to not put wash-water in with their oil, the
quality increased significantly.
4. The Nature of Vegetable Oil- WVO has a tendency to harden over time when in contact with the air,
causing a buildup of crusty black oxidized oil on everything it touches (think of linseed oil). This creates
a challenge in keeping pumps, hoses, trucks, etc., clean
5. Combustion - WVO burns very well, but creates several unique problems. Between heating cycles
(when the burner is not running), the burner nozzle is exposed to very high heat radiating back from
the combustion chamber of the boiler. A small bit of residual oil still inside the nozzle can carbonize
and create a creosote-like buildup inside the nozzle. Even worse, a thick waxy substance precipitates
out of the oil within the nozzle which can clog the nozzle within a matter of days. Several spare nozzles have to be kept on hand, and the nozzles must be changed and cleaned on a rigorous schedule or the
spray pattern will begin to deteriorate causing incomplete combustion, soot, and oil buildup on the
burner assembly.
6. Energy Density - Vegetable oil has approximately 10% less energy per unit of volume than home
heating oil. This means the boiler produces approximately 10% less energy than its rating when
burning WVO than when burning petroleum.
Waste Motor Oil
Waste motor oil is a recycled product and is appropriate for use in our clean burn boiler. Overall, motor oil
burned very well and reliably in our boiler.
The only problem encountered with motor oil was when sludgy thick oil was not sufficiently filtered.
Home Heating / Diesel Oil
All home heating oil we tried burned reliably with no problems.
Bio-diesel
We did not have a reliable source of 100% bio-diesel. When we briefly tested it, it burned reliably with no
problems.
High-Efficiency Hydronic & Root Zone Heat
In our system, we used different methods to apply heat:
For greenhouses, we used the Delta-T system (EPDM
tubing) for both bench and under-floor heat and we also
used PEX under-floor hydronic heat. For work spaces, we
used baseboard hot water and also hot water unit heaters.
All systems draw heat from our primary boiler through a
series of primary, secondary, and tertiary loops and heat
exchangers - See diagram.
Here is a list of important design considerations and
features of our system:
1. The Clean Burn boiler is a central heat source. It is a
350,000 BTU / Hour waste oil boiler. It is located in
our barn and is about 150 feet from our heated
greenhouses. The Boiler has a primary loop that circulates water through a manifold that supplies heat
to the office and work spaces. The primary loop also feeds a 300 foot long run of 40mm PEX tubing
(greenhouse loop) that delivers approximately 140,000
Btu / Hour to our greenhouses.
Both the main Boiler and loops and the greenhouse
water use a 30% glycol solution to protect from freezing
in the even the system is off due to power failure, etc.
2. The greenhouse loop circulates water from the boiler to
a heat exchanger that transfers the heat to the
greenhouse water. The bench heat uses EPDM tubing
which is not impervious to oxygen. Because of this, the
fluid Circulating in the greenhouses can contain
corrosive oxygen and must be isolated from the boiler.
The greenhouse heat is comprised of the indirect hot water heater and an auxiliary residential grade
boiler that provides an additional 120,000 BTU / hour connected in series with a distribution loop. The
oil fired heater burn home heating oil and provides backup heat in the event that the Clean Burn boiler
fails or auxiliary heat for very cold weather. These two tanks serve to store heat, and from them the
water is distributed through mixing valves to provide 140 degree water to each of 3 greenhouses.
a. The first greenhouse (Koko) uses bench heat - a Delta-T heat system which is an industry
standard bench heat system. Two 4' benches run the length of the greenhouse are heated
with tubing on 2" spacing. This provides about 90 BTU's / Hour per square foot for a total
maximum of approximately 25,000 BTU / Hour. This greenhouse has a single layer of
polycarbonate covering
b. The second greenhouse (Gatemouth) also uses the Delta-T system. It is a combination of one
bench - 5 x 80 feet, and a heated floor area approximately 10 x 60 feet. In the floor system the
Delta-T system is embedded in about 2" of crushed stone and insulated by a double bubble
insulation layer beneath it. This greenhouse uses an inflated double layer of PE greenhouse
film.
c. The third greenhouse uses PEX tubing embedded in the floor. The system has 4" of expanded
polystyrene insulation below the floor, about 3 inches of crushed stone with the PEX loops on
9" centers tubing embedded in it, and pavers for thermal mass. There is a 4 inch wide thermal
barrier around the periphery of the house that extends 18" into the ground. This house is
intended to be our warmest house, where we keep tender plants. It is covered with twin wall
polycarbonate.
The figure below shows a worst case analysis of the greenhouse heat loads. (NOTE: The analysis includes
additional hot water unit heaters. These were not included as the bench and floor heat provides sufficient heat
in the coldest weather.)Baseboard and Hot Water Unit Heater Heat
We also used baseboard heaters in our existing offices and small forced air
unit heaters in our lunch room. All of these provide adequate heat for the
space. The table below shows the computed heat loads for each space. Under
floor hydronic heat would be preferable because it is typically more efficient
than baseboard heat, but was not an option in our already-built office spaces.
Back-Up and Auxilliary Heat
Based on the model, above, we knew that the worst case amount of heat
required by the greenhouses (252AOO btu / hr.) would be greater than the
amount of heat that can be delivered through the underground path (about
200,000 btu / hr.) We also desired to have a secondary source of heat in case
of failure of the Clean Burn boiler or any associated systems. Therefore we
implemented a backup boiler. This system consists of:
• A Used Sears 120,000 btu / hr. residential boiler
• A 275 gallon oil tank
• Circulator and controls
• Heat Exchanger
This system is housed in a small building built to hold it along with
all the greenhouse heat circulator pumps and controls.
This is designed to come on at a lower temperature than the
{normal' hot water temperature. The secondary boiler comes on at
about 1400 F and runs until the water reaches 1600 F. This runs
autonomously, and will come on whenever the water temperature
drops, whether the drop is due to extreme cold temperatures or due
to the Clean Burn boiler tripping off.
Photo 7 - Building for Backup and
Greenhouse Manifolds While the secondary boiler does not have sufficient capacity to keep
the greenhouses at optimum temperatures by itself it will keep the
houses and the rest of the heating system above freezing on even the coldest nights.
Comparative System - Heartwood Nursery
During the time this project was underway, nearby Heartwood Nursery built a new propagation house.
The greenhouse itself is innovative: It was constructed as a traditional wood post and beam shed building and
the Nursery Owner had it covered with twin wall polycarbonate rather than sheet metal. The result was a very
tight and well insulated greenhouse as well as saving considerable money as compared to a traditional gothic
greenhouse structure. The prop house is 40 feet x 70 feet, and the owner specified two heated benches at 10
feet x 40 feet each.
For this system, reliability was critical. Heat modeling suggested the greenhouse would require less than
l00,000 BTU / Hour, and we also wanted to heat a workshop building that would house the boiler. In order to
have some reserve capacity and allow for future growth, we chose a Burnham 200,000 BTU / Hour residential
oil-fired boiler. Similar to Emory Knoll Farms, the workshop the houses the boiler is about 300 feet from the
greenhouse. A loop of 1" PEX tubing buried in an insulated pipe runs from the workshop to the greenhouse
and feeds a flat plate heat exchanger at the greenhouse.
The Heartwood greenhouse heat is also a Delta-T bench heat system. The nursery owner wanted to reuse
as many components from their old site as possible. We were able to use a thermostatic control system, and
zone valves and incorporate them into the new system allowing for four separate zones on the benches. Later,
to improve reliability and simplicity, the zones were eliminated and both benches are heated from a single
control.
Provisions for hot water unit heaters were included in the design for both the workshop and the
greenhouse. In the final implementation, we learned that unit heaters were not required in the greenhouse
and a single 50,000 BTU / Hour unit heater was sufficient for the workshop. The diagram below shows the
system and calculated worst case heat loads. Comparative System - Green Meadow Farm
Green Meadow Farm has been heating greenhouses with WVO for many years. They grow organic produce
in the summer, and organic greens & specialty root vegetables in heated houses in the winter for restaurants in
the Philadelphia area. Owner Glenn Brendle has been an inspiration to our adoption of WVO heating and a
source of technical and practical expertise.
Green Meadow Farms originally used a typical outdoor wood-fired furnace that had been modified to burn
WYO. About the time our project began, they switched to a new heating plant comprised of two Clean Burn
CBT-350 boilers, the same model we are using. They also have the advantage of being close to the
manufacturer, Clean Burn, Inc. They collaborated with the engineers at Clean Burn to modify the boilers for
use with WYO. Their early success at using WVO in a Clean Burn boiler gave us confidence that our choices
would work, even as we experienced difficulties in implementing our project.