Integration of air handling and heat pump: by no means obvious

'It's all about the right balance between comfort, investment and energy consumption'

The traditional combination of an air handling unit and a boiler/water chiller is becoming a less and less chosen solution with the advance of the direct expansion (DX) heat pump. Especially the price aspect makes the one-two punch between a CHP unit on the one hand and a DX inverter heat pump on the other increasingly popular. Nevertheless, the choice for such a system is not always obvious and there are several points of interest when purchasing it. Harry van Veen, director of Horos Klimaattechniek from Soest, lists the most important ones. 

Since 1952, Horos Klimaattechniek has offered a wide range of indoor climate solutions for utilities and industry. The company mainly supplies high-quality products in air treatment, cooling and humidification. In these areas, Horos frequently answers questions about indoor climate and industrial applications. 

Choice 

In recent years, this has been happening mostly when the combination between an (inverter) heat pump and air treatment has been mooted as the ultimate solution. "With the introduction of the heat pump at the end of the last century, smaller users in particular are opting less and less for passive cooling using a cold source for the summer and a water-to-water heat pump for the winter that may or may not be connected to the same source, respectively," Van Veen said. "An excellent solution, especially when you consider the purchase price of the equipment and installation. After all, you no longer need a circuit for chilled water, with all the associated fittings such as buffer vessels, pumps and expansion vessels. In addition, you're talking about a system that comes plug and play in most cases."

Side note

The switch from water chiller to (inverter) heat pump offers installers and end-users alike some pluses. But it's not all gold that glitters. Indeed, with over 70 years of experience in the baggage, they see at Horos that the market often overlooks certain issues. This is precisely why comfort and controllability - and thus the reliability of the installation - can be compromised, Van Veen believes. "The big advantage of a water chiller as a heat pump is that you can very accurately modulate its capacity from 0 to 100 percent using a control valve. A DX heat pump you can also control modularly, but only from about 25 percent."

Second, a heat pump is always explained on cooling capacity in the summer months. "This means that in winter you always have overcapacity, simply because then the required heat capacity is smaller than the cooling capacity you need in summer," Van Veen explains. "As a result, in the cold months a heat pump is running in the lower part of its regulation. After all, less power is required then. When the requested capacity falls below a certain level, the heat pump shuts down, resulting in temporarily colder air being blown into your building."

Third, a heat pump must regularly defrost in winter. Because this causes the system to reverse its cycle, the intake air temperature can drop below 10ºC and create drafts. Van Veen: "An inconvenience that may be short-lived, but is of course far from comfortable. As a solution, you can divide the heating capacity into several circuits. A comfort-enhancing, but at the same time a more costly affair."

Happy end user

Van Veen's account shows that the relatively inexpensive combination of an inverter heat pump with an air handling unit is not a given. Other solutions and options are also conceivable, he says. "One can think of an air/water heat pump, for which EIA subsidy can be obtained. But also the combination of air handling unit with a reversible water chiller is and remains possible. The key is to find the right balance between comfort, monetary investment and energy consumption. And that can be done in different ways. The end user must be happy. That is our main focus."

ISDE and EIA subsidies
Air-cooled water heat pumps <400 kW are subject to ISDE subsidy, which can be up to €34,000. EIA subsidy applies to plug and play WTWs equipped with integrated and external DX heat pumps.