Heat Recovery

For several years this subject has been met with an increasing interest also within our industry. HAAS-MEINCKE A/S - the world's largest oven producer - has therefore, together with the Technical University of Denmark, investigated if not only new, but also existing ovens can be optimized with regard to energy consumption.

The result of the calculations was in addition tested at a customer in Scandinavia for several months. The tests were made on an oil heated oven, but in principle the conclusions can also be applied to ovens heated by gas, and what is more surprising to ovens heated by electricity. The result is very positive as it is possible to achieve savings of 10-15%.

Please find below the results and conclusions from the tests. The heat recovery unit can be installed in each zone, but it is not necessary to install it in all zones. The basic requirement is a temperature of at least 150°C per zone and the fresh air intakes must be more than 60% open.

Calulation of your savings

If you are interested, we would be pleased to make calculations for your oven to see if the heat recovery unit is profitable.  For these calculations we would need the following information:

·        baking temperature in each zone

·        position of fresh air intake

·        actual consumption per zone

·        quantity of exhaust air

·        temperature of exhaust air

·        humidity content of exhaust air

·        quantity of fresh air intake

·        humidity content of room air

·        air pressure (ie height beyond sea level)

·        consumed burner effect

The more of above parameters we know, the better. Some of the figures can be evaluated based on heat exchanger type and damper adjustment (on our own ovens), product type and quantity, baking temperature and height beyond sea level. In most cases the cost savings will be 10-15%.

Test results from Scandinavian customer

At the same time we are pleased to show you the actual measurements of a Scandinavian oven (30 x 1.5 m, 3 zones, oil fired) and the realistically achieved savings. The measurements were made both before and after the installation of the heat recovery unit.

Oven settings as follows:

         Zone 1: 250°C, 50% top heat, 0% fresh air

         Zone 2: 245°C, 70% top heat, 90% fresh air

         Zone 3: 265°C, 70% top heat, 100% fresh air

         Baking time 6.9 min 70 rows/min, 20 products/row

The heat recovery unit was mounted on a 300 kW burner section with approx 120 kW fired power.

Measured consumption on zone 3:

         Oil consumption before   ~ 11.65 l/h

         Oil consumption after     ~   9.96 l/h

         Saving 1.69 l/h ~ 14.4% (15%)

         Transferred power = 18 kW

A heat recovery unit mounted on a 150 kW burner section with approx 75 kW fired power ~ 7 l/h or 7 m³ natural gas/h will give a saving ~ 1 l oil/1m³ natural gas/h.

         Saving ~ 15%

         Transferred power = 12 kW

The above results will be the guidelines in the vast majority of cases and be valid irrespective of fuel type. As a rule-of-thumb the heat recovery unit is a reasonable solution if the fresh air damper is 60% or more open and the baking temperature beyond 150°C.

The heat recovery unit is presently not suitable for the use of DGF ovens, cyclotherm ovens or by baking/drying at temperatures less than 150°C. Our R&D department is working on the implementation of the heat recovery unit on both oven types (DGF and cyclotherm).

We are looking forward to further reducing the energy consumption of your HAAS-MEINCKE oven together with you.